Effects of monochromatic LED light qualities on the photosynthetic capacity and pigment content of Dunaliella salina

Effects of monochromatic LED light qualities on the photosynthetic capacity and pigment content of Dunaliella salina | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Effects of monochromatic LED light qualities on the photosynthetic capacity and pigment content of Dunaliella salina Tianze Zhao, Yongfu Li, Xingkai Che, Haixing Wu, Yuchen Ye, Dingning Fan, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5450150/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract Light quality is a crucial abiotic environmental factor that influences the growth and β-carotene accumulation on Dunaliella salina . However, the influence of the factor on the primary photochemical reactions of D. salina and the physiological mechanisms regulating β-carotene metabolism remains unclear at present. This study involved the batch culture of D. salina using low light (40 ± 5 μmol photons m -2 s -1 , without inhibiting photosynthetic electron transfer) provided by different colored LEDs. Our results indicated that the growth rate, chlorophyll a/chlorophyll b/β-carotene content of D. salina cells were higher under BL and RL than under WL and GL. The light absorption rates of chloroplasts in algae cells under BL and RL (22.8% and 18.6%, respectively) were higher than those under WL and GL (14.0% and 10.2%, respectively), which was attributed to the reduced light energy dissipation and increased photochemical efficiency under BL and RL. BL and RL enhanced the photosynthetic efficiency and β-carotene synthesis capability of D. salina cells. It was observed that under low light, light quality has little influence on the synthesis process of β-carotene. However, two key genes involved in the degradation pathway of β-carotene ( LUT5 and ABA2 ) are significantly downregulated under both BL and RL. The higher content of all-trans β-carotene under BL than under RL. This is attributed to the inhibition of the conversion pathway from all- trans β-carotene to ABA biosynthesis precursor (9- cis -β-carotene) is more pronounced under BL than under RL. This explains why D.salina has a higher content of all- trans β-carotene under BL, while synthesized more 9- cis -β-carotene under RL. Dunaliella salina light quality photosynthesis Chl a fluorescence transient all-trans β-carotene Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1. Introduction Dunaliella salina is a salt-tolerant single-cell eukaryotic green alga that could accumulate large amounts of β-carotene under stress conditions such as strong light (Guermazi et al., 2023 ; Xi et al., 2021 ), high temperature (Gómez and González, 2005 ), high salt (Guermazi et al., 2023 ), and nitrogen deficiency (Kevin and Widjaja, 2023 ). It is currently considered a promising source for the industrial production of natural β-carotene. Carotenoids are primarily stored in the cytoplasmic lipid droplets of D. salina (Kim et al., 2024 ), accounting for up to 10% of the dry weight of D. salina cells (Murthy et al., 2005 ; Lam and Lee, 2014 ; Lamers et al., 2010 ). Today, the large-scale cultivation of D. salina primarily occur in outdoor open ponds, mostly in Australia, Israel, and China (Del-Campo et al., 2007 ; Borowitzka, 2013 ; Li et al., 2020b ). β-carotene can scavenge potentially harmful free radicals and protect the immune system (Götz et al., 1999 ). It is commonly used as a dietary supplement for both humans and animals (Pulz and Gross, 2004 ), as well as a raw material for biologics (Huang et al., 2024 ; Mizobuch et al ., 2023). Additionally, it plays an active role in preventing and alleviating Alzheimer's disease, Parkinson's disease, vitamin A deficiency (VAD), gastrointestinal cancer, pancreatic cancer, breast cancer, and other diseases (Fiedor and Burda, 2014 ; Grune et al., 2010 ; Leo and Lieber, 1999 ). β-carotene primarily exists in the form of isomers such as all- trans , 9- cis , 13- cis , and 15- cis (Wang et al., 1994 ). Currently, all- trans β-carotene is obtained mainly using chemical and biotechnological methods (Papaioannou and Liakopoulou-Kyriakides, 2012 ; Harvey and Ben-Amotz, 2020 ). The β-carotene cis isomers are believed to be more bioactive than all- trans β-carotene (Harvey and Ben-Amotz, 2020 ). Previous studies have demonstrated that the β-carotene cis isomers may serve as an effective treatment for a range of malnutrition-related conditions like type II diabetes, chronic plaque psoriasis, and atherosclerosis (Greenberger et al., 2012 ; Harari et al., 2013 ; Relevy et al., 2015 ). Also, the β-carotene cis isomers can expand the antioxidant capacity of algal cells and more effectively protect reaction centers (RCs) from damage by reactive oxygen species (ROS) (Honda, 2021 ). As a result, these isomers are attracting increasing attention from researchers. A high density of D. salina cells is crucial and essential for the natural production of β-carotene (Fu et al., 2013 ). The traditional industrial model of using outdoor open ponds to cultivate D. salina and accumulate natural β-carotene is gradually becoming inadequate to meet the growing demand for the substance. Open ponds do not allow light and temperature to be manipulated, making it difficult to bring the cell density of D. salina cells up to 1 × 10 6 cells mL − 1 (Ben-Amotz, 1995 ). In order to increase the cell density of D. salina and achieve a higher natural β-carotene yield, Hejazi et al. ( 2004 ) modified to the cultivation process and target product extraction process of D. salina . That was achieved through a change from open cultivation to closed photobioreactors, which facilitated easier artificial regulation of the expanded cultivation of D. salin a. Prieto et al. ( 2011 ) analyzed the effects of cultivation methods (batch and semi-continuous) and types of photobioreactors (open and closed) on carotenoid productivity in D. salina , finding that the highest carotenoid yield was achieved in a closed tubular photobioreactor. Díaz et al. ( 2021 ) optimized their previously-designed closed tubular photobioreactor, based on the Fibonacci type, and assessed its performance in producing green D. salina under environmental conditions in the Atacama Desert. The study achieved the maximum biomass productivity of D. salina under strong light. Currently, utilization of photobioreactors for the cultivation of D. salina cells to produce β-carotene has emerged as a focal point in research on microalgae cultivation. Compared to outdoor open ponds, photobioreactors have advantages like controllable cultivation conditions, short light paths, use of artificial light sources to supplement light energy, high mixing efficiency, and convenient CO 2 supply (Ma et al., 2024 ; Chen et al., 2024 ; Tredici, 2004 ). Thus, photobioreactors feature higher photosynthetic efficiency and production capacity (Prieto et al., 2011 ). Nowadays, the two-stage cultivation method is primarily utilized for cultivating D. salina cells to produce β-carotene (Ben Amotz, 1995; Borowitzka and Borowitzka, 1989 ; Borowitzka, 2013 ). In the initial stage known as the green cell stage, D. salina cells are cultivated in an environment that enables rapid growth and biomass accumulation. Subsequently, D. salina cells are transferred to and cultivated under stress conditions such as high light, high temperature, and nitrogen deficiency to enhance carotenoid production and yield. This stage is referred to as the yellow cell stage. Closed photobioreactors can have a positive impact on carotenoid production during both the green cell stage and β-carotene accumulation stage (Prieto et al., 2011 ). In large-scale cultivation using photobioreactors, the management of artificial light sources is a key technical issue that needs to be addressed first (Rozenberg et al., 2024 ; Rodríguez-Bolaños et al., 2024 ). Light intensity and wavelength are critical factors that influence the selection of artificial light sources. Light emitting diodes (LEDs) have attracted attention in microalgae cultivation and are considered suitable light sources as they make it easy to control spectral quality and have high energy efficiency (Lima et al., 2021 ; Li and Liu, 2020 ). LEDs with different spectra, such as red, blue, white, and green, have become widely utilized in microalgae cultivation (Molina-Miras et al., 2018 ; Zhao et al., 2013 ; Chen et al., 2015 ). In recent years, researchers have conducted D. salina cultivation experiments by altering the wavelength of light source. These experiments aimed to investigate the effects of wavelengths on the growth, photosynthetic activity, and β-carotene accumulation of D. salina cells. Lan et al. ( 2022 ) utilized red light to enhance the expression of LCYB gene in green D. salina cells, leading to an increase in β-carotene content. Similarly, Mirzaie et al. ( 2021 ) developed a red-blue flash light conversion system based on the growth curve of D. salina cells to promote β-carotene synthesis. Sui et al. ( 2021 ) conducted a comparison of β-carotene production between two types of D. salina under different wavelengths of light (red, blue, and white). Their findings revealed that red light can increase the weight percentage of 9- cis /all trans β-carotene in D. salina cells. In a separate study, Mohebi-Najafabadi and Naeimpoor (2023) investigated the effects of red light and blue light (monochromatic, or mixed) on the content of β-carotene in D. salina cells during two stages of cultivation. However, to date, there have been limited studies focusing on the effects of light quality on the levels of β-carotene cis isomers and the expression of key genes in β-carotene metabolic pathway within D. salina cells. It remains unclear whether the β-carotene degradation process in cells is affected by light quality. In this study, we investigated the effects of monochromatic LED light quality on the photosynthetic activity and β-carotene metabolism of D. salina during the green cell stage through Chl a fluorescence transient measurement and transcriptome sequencing. We also sought to determine the expression levels of key enzyme genes involved in the synthesis and degradation of β-carotene in D. salina cells under different light conditions. This will help reveal the mechanism by which light quality regulates β-carotene accumulation in D. salina . The findings from this study will provide a scientific basis for the technology of large-scale D. salina cultivation and efficient accumulation of β-carotene in closed photobioreactors. 2. Materials and methods 2.1 Culture and treatment of plant materials The Dunaliella salina strain (IOCAS 879ss) was obtained from the Institute of Oceanology, Chinese Academy of Sciences, and batch-cultured in the modified Johnson medium (Borowitzka, 1988). Algae were pre-cultured under the following conditions: temperature 30 ± 1℃, light intensity 80 ± 10 μmol photons m -2 s -1 provided by white light-emitting diodes (LEDs) under a 12-hr light/12-hr dark cycle. During the growth phase, the cultures were manually shaken three times per day to avoid sticking. 2.2 Light treatments during batch cultivation To explore the effects of various light qualities, a batch culture was established in a precision multi-light quality combination-tuned light incubator (Taizhou Haijiang Bioengineering Technology Co., Ltd., China), with a controlled cultivation temperature of 30 ± 1 ℃ and a light-dark cycle of 12h:12h. The illumination was provided by four artificial light sources of different spectral regions, i.e., blue LED strips (for blue light, BL), red LED strips (for red light, RL), white LED strips (for white light, WL), and green LED strips (for green light, GL), respectively. To guarantee the purity of the light qualities, experiments under different light resources were carefully separated using lightproof steel plates. A Spectral Scintillation Illuminometer (OHSP-350SF, Hangzhou Hongpu Light Color Technology Co., Ltd., China) was used to measure the spectra of the artificial light sources within the light incubator at a resolution of 1 nm between 350 and 700 nm (Supporting Information: Figure S1). An equation for the relationship between the incident light intensity (I in ) and the average light intensity (I av ) received by algal cells was set up using the simplified Lambert Beer law (Chen et al ., 2011). where I in represents the incident light intensity, I av represents the average light intensity received by algal cells, and T represents the transmittance (%), i.e., the ratio of the emitted light intensity to the incident light intensity. D. salina cells in the green cell stage were cultured in the light incubator. The average intensity of artificial light received by D. salina cells in each of the light quality zones was kept at 40 ± 5 μmol photons m -2 s -1 . Research has indicated that intense light at 800~1200 μmol photons m -2 s -1 can result in significant light damage to D. salina , leading to impaired or even interrupted photosynthetic electron transfer in algal cells (Qin et al ., 2021). This makes it difficult to analyze differences in light energy allocation and utilization in D. salina under different light qualities. Therefore, we chose weak light (40 ± 5 μmol photons m -2 s -1 ) for our experiments based on the studies that suggest neither serious photo inhibition nor significant impairment to photosynthetic electron transfer occur in D. salina cells under a light intensity of 50 μmol photons m -2 s -1 (Sui et al ., 2019; Capa-Robles et al ., 2021; Kim et al ., 2024). The use of weak light below 50 μmol photons m -2 s -1 helps analyze differences in β-carotene metabolism under various light qualities in D. salina cells. Three biological replicates were set up under each light quality. Green algal cells were cultured for 15 days, with the culture collected every 3 days to determine algal cell density and photosynthetic pigment content. On the 15th day, all green algal cells were harvested to measure cellular light absorption, Chl a fluorescence transient, and intracellular contents of β-carotene and its cis isomers. Also, quantitative Polymerase Chain Reaction (qPCR) analysis and transcriptomic analysis were carried out. 2.3 Measurement of cell density and specific growth rate The cell density was manually counted using a hemocytometer and an inverted microscope (Shanghai Optical Instrument Factory, Co., Ltd., China) with 37 XB magnification. The specific growth rate (μ) of D. salina cells was calculated using the following formula (Moheimani and Parlevliet, 2013): where N 2 (final) and N 1 (initial) are the cell densities (cells mL -1 ) determined using a hemocytometer at the times T 2 and T 1 , respectively. 2.4 Measurement of pigment content The improved ethanol extraction method (Danesh et al ., 2017) and spectrophotometric method proposed by Arnon (1949) were used to measure the contents of chlorophyll a (Chl a) and chlorophyll b (Chl b) in the culture. Briefly, 5 mL of culture media was centrifuged at 10,000 g for 10 min using a centrifuge (TGL-16 M, Changzhou Jintan Liangyou Instrument Co. Ltd., China). After the supernatant was removed, the cell pellet was dissolved in 5 mL of 95% ethanol and extracted under darkness for 24 h. Then, the extract was centrifuged at 10,000 g for 10 min at 4℃. The resulted supernatant was used for the quantization of pigments as follows: where A represents the absorbance at the indicated wavelength. 2.5 Measurement of light absorption and Chl a fluorescence transient The average extinction coefficients at different wavebands, i.e., BL (400–480 nm), GL (500–560 nm), RL (600–650 nm), and photosynthetic active radiation (PAR, 400–700 nm), were determined as described by Li and Meng (2014). Microalgae precultured in LED white light as described in the “Culture and treatment of plant materials” section were used to determine the light absorption to avoid the possible influence of light acclimation on light absorption. The transmittances were recorded by scanning the supernatant. The average light transmittance ( T ) and mean extinction coefficient ( a ) of the algal suspension were calculated with the equation below. where λd and λu are the lower-limit wavelength and upper-limit wavelength of each light quality, respectively; T(λ) represents the monochromatic light transmittance of each wavelength (%); S(λ) is the relative spectral power distribution on the corresponding wavelength (W); V(λ) stands for the efficiency of spectral illumination of the corresponding wavelength. The values of S(λ) and V(λ) can be obtained from the information given by the International Commission on Illumination (CIE) and the National Standardization Technical Committee (2008). According to CIE, the sampling interval established to obtain values of S(λ) and V(λ) is 5 nm in the range 400–700 nm. The specific extinction coefficient of mixed light quality was expressed as the average value of each monochrome light quality. Ae refers to the proportion of the incident light absorbed by algal suspension or pigment extract. The cuvettes containing the algal suspension under different light qualities were initially dark adapted for 20 min. Then, the Chl a fluorescence transient was measured using the FluorPen software (AquaPen Ap110-C, Czech Republic) according to Li et al . (2024). Saturated red light at 3000 μmol photons m -2 s -1 was produced by an array of light-emitting diodes (LED, peak 650 nm). The Chl a fluorescence transient was obtained using 2 s of saturated red light, and analyzed with the OJIP transient in line with the OJIP-test procedure proposed by Strasser and Strasser (1995). The relevant Chl a fluorescence transient parameters and their biological significances revealed by the JIP test are shown in Table 1. Table 1 Chl a fluorescence transient parameters ( Strasser et al . 2004 ) Parameters Biological significance Fv/Fm Maximum photochemical efficiency of the PSII PI ABS Performance index on absorption basis ABS/RC Absorption flux per RC TR 0 /RC Trapped energy flux per RC (at t=0) ET 0 /RC Electron transport flux per RC (at t=0) DI 0 /RC Dissipated energy flux per RC (at t=0) 1-Vj Probability (at t = 0) that a trapped exciton moves an electron into the electron transportchain beyond Q A − 2.6 Measurement of algal cell size 2 mL of the agal culture was centrifuged at 10,000 g for 10 s using a centrifuge (TGL-16 M, Changzhou Jintan Liangyou Instrument Co. Ltd., China) to concentrate the algal cells. The algal cells were observed and imaged under an inverted microscope (Shanghai Optical Instrument Factory, Co., Ltd., China) at 37 XB. The open-source platform Image J (Rasband, 2012) was used for image analysis and the measurement of algal cell area (μm 2 ) and diameter (μm). Forty cells were randomly selected per light quality to determine their areas and diameters. 2.7 Measurement of β-Carotene and its geometric isomers The contents of β-carotene and its geometric isomers were determined through high performance liquid chromatography (HPLC) (Priscilla et al ., 2024; Mazzucchi et al ., 2020). The specific chromatographic conditions were as follows: high-performance liquid chromatograph: Agilent 1260 Infinity II; chromatographic column: C30 YMC TM Carotenoid (4.6 mm×250 mm, 5 μm); mobile phase A: acetonitrile-methanol (3:1, V/V), with the addition of 0.05% triethylamine (V/V), treated through ultrasonic degassing before use; mobile phase B: MTBE (methyl tert-butyl ether), with the addition of 0.05% triethylamine (V/V), treated through ultrasonic degassing before use; gradient: within 8 min, the content of mobile phase B increased linearly from 0% to 55%, and then maintained at 55% for another 27 min; flow rate: 1.0 mL/min; detection wavelength: 475 nm; injection volume: 20 μL; column temperature: 30 ℃. 2.8 Quantitative Polymerase Chain Reaction The RNA of the algal cells cultured under different light conditions for 15 days was extracted using the Total RNA Extraction Kit (AikeRui Biotech, China). The first-strand cDNA was synthesized using the First-Strand cDNA Synthesis Kit (Tiangen, Beijing, China), and the full-length coding sequence of the gene was cloned from the cDNA. Real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis was performed according to the MIQE guidelines (Bustin et al ., 2010) using a fully automated fluorescence quantitative PCR system. The qRT-PCR thermal cycling conditions were as follows: pre-denaturation at 95°C for 30 s, followed by 40 cycles of denaturation at 95°C for 5 s, annealing at 60°C for 15 s, and extension at 72°C for 20 s. Primers were designed according to Li et al . (2020a), with β-Tubulin used as an internal reference gene. The primer sequences are listed in Supporting Information: Table S1. Three biological replicates were performed for each gene, and statistical analysis was conducted using the standard curve method. 2.9 Transcriptomic analysis RNA sequencing and standard bioinformatic analyses were carried out by Biomarker Technologies Co., Ltd. (Wang et al ., 2009). In brief, total RNA was extracted from DN and DH treatment samples, and first‐strand cDNA was synthesized using random hexamer primer and M‐MuLV Reverse Transcriptase. To select cDNA fragments of preferentially 240 bp in length, the library fragments were purified with the AMPure XP system (Beckman Coulter). Then, 3 μL of USER Enzyme (NEB) was used with size‐selected, adaptor‐ligated cDNA at 37°C for 15min followed by 5min at 95°C before PCR. Thereafter, PCR was performed with Phusion High‐Fidelity DNA polymerase, Universal PCR primers, and Index (X) Primer. Finally, PCR products were purified (AMPure XP system) and library quality was assessed on the Agilent Bioanalyzer 2100 system. On that basis, the libraries were sequenced using an Illumina Hiseq X‐ten platform, PE 240 bp. The sequences were further processed with a bioinformatic pipeline tool, BMKCloud (www.biocloud.net) online platform. Gene functions were annotated based on the following databases: NR (NCBI nonredundant protein sequences), Pfam (Protein family), KOG/COG/eggNOG (Clusters of Orthologous Groups of proteins), Swiss‐Prot (A manually annotated and reviewed protein sequence database), KEGG (Kyoto Encyclopedia of Genes and Genomes), and GO (Gene Ontology) (|log 2 FC | > 1, false discovery rate (FDR) < 0.05). Each sample had three replicates and the annotation was repeated three times. GO pathway enrichment analysis and KEGG pathway enrichment analysis were performed through the topGO R packages‐based Kolmogorov–Smirnov test and KOBAS software, respectively. The raw sequence reads have been deposited in the NCBI database under the accession number PRJNA856777. 2.10 Statistical analysis Data in the figures, representing the averages of replicates ± standard deviation (SD), were subject to one-way ANOVA complemented by a least significant difference post hoc test, which was conducted using the software SPSS Statistics 26.0. All the data were tested for normality and homogeneity of variance to check whether they meet statistical requirements. When a significant difference was found, a post-hoc comparison-of-means test (Tukey or Games-Howell test) would be carried out to determine which values differed significantly. A p -value below 0.05 was considered statistically significant. 3. Results 3.1 Effects of light quality on algal cell growth and pigment content During the 15-day cultivation period, the algae showed logarithmic growth under all four light qualities, with the highest cell density observed under BL (Fig. 1 A). The maximum specific growth rate µ (0.066 ± 0.005 d − 1 ) was also observed under BL, slightly higher than the specific growth rates under WL (0.063 ± 0.007 d − 1 ) and RL (0.060 ± 0.005 d − 1 ), and significantly higher than that under GL (0.050 ± 0.004 d − 1 ) (Fig. 1 B). BL considerably increased the contents of Chl a and Chl b in both algal culture and cells (Fig. 1 C, D). This indicates that BL is more conducive to algal cell division, proliferation, and chlorophyll synthesis. 3.2 Light absorption of D. salina in different spectra For D. salina cells, the light absorption (Ae) at all the four wavelengths is relatively low, with no more than 40% of incident light being absorbed (Table 2 ). However, there is a significant difference in the light absorption rate and pigment extracts of D. salina cells at different wavelengths. The highest Ae value for D. salina cells is observed in the blue wavelength (37.9%), followed by the white (31.3%), red (22.8%), and green (22.1%) wavelengths. As for pigment extracts, the highest Ae value is also in the blue wavelength (22.8%), followed by the red (18.6%), white (14.0%), and green (10.2%). This indicates that both D. salina cells and pigments absorb more light energy in the blue wavelength than in the other wavelengths. Table 2 Average transmittance (T: %) and proportion of absorbed incident light (Ae: %) of cells and pigment extracts in Dunaliella salina at different wavebands, namely white light (WL, 400 ~ 700 nm), blue light (BL, 400 ~ 500 nm), red light (RL, 570 ~ 680 nm) and green light (GL, 450 ~ 600 nm), respectively Algal cells Pigment extracts Ratio of pigment absorption to cell absorption/% Light source T/% Ae/% T/% Ae/% BL 62.1 37.9 77.2 22.8 60.3 GL 77.9 22.1 89.8 10.2 46.4 WL 68.7 31.3 86.0 14.0 44.7 RL 77.2 22.8 81.4 18.6 81.8 3.3 Effects of light quality on photosynthetic efficiency The fluorescence intensity of the OJIP curve of D. salina cultivated under BL was much higher than those under other light qualities (Supporting Information: Figure S4). Different light qualities greatly affected the photosynthetic capacity of D. salina cells and the light energy absorption of PSII reaction centers (RCs). The highest values of Fv/Fm and PI ABS were observed under BL, exceeding those under the other light qualities. On the other hand, the values of Fv/Fm and Pi_ABS under GL were lower than those under the other light qualities. This indicates that BL can increase the photosynthetic capacity of D. salina and improve the photosynthetic efficiency of RC, whereas GL is not conducive to expanding the photosynthetic capacity. Similarly, the ABS/RC, TR 0 /RC, ET 0 /RC, and 1-V J values under BL were all higher than those under the other light qualities, while the values under GL were at relatively lower levels. However, in terms of the DI 0 /RC value under GL was higher than those under the other light qualities. This suggests that BL increased PSII RCs’ capability to absorb, capture and transfer light energy while reducing energy dissipation. Attributed to that, PSII RCs are more efficient in utilizing light energy under BL than under the other light qualities. On the contrary, under GL, PSII RCs reduced their capability to absorb, capture and transfer light energy while increasing energy dissipation. That resulted in a lower utilization efficiency of light energy (Fig. 2 ). 3.4 Effects of light quality on contents of β-carotene isomers Significant differences in the pigment ratio of D. salina under different light qualities were observed (P < 0.05) during the 15-day cultivation period. Under BL, the ratio of antenna pigments (Chl b + Car) to reaction center pigments (Chl a) reached a maximum of 0.87, followed by 0.83 under RL and 0.78 under WL. The lowest pigment ratio, 0.72, occurred under GL (Fig. 3 A). This indicates that BL is more favorable for the absorption and transfer of solar energy in D. salina cells compared to the other light qualities. Through HPLC analysis, three geometric isomers of β-carotene were identified: all- trans β-carotene, 9- cis β-carotene, and 13- cis β-carotene. Significant differences were noted in the contents of β-carotene and its cis isomers within both algal suspension and cells under BL, RL, and WL (P < 0.05). The highest concentration of all- trans β-carotene in algal suspension, 11.46 mg L − 1 , occurred under BL, much higher than the concentrations recorded under RL (9.41 mg L − 1 ) and WL (2.46 mg L − 1 ). However, RL resulted in substantially higher levels of both 9-cis β-carotene (5.09 mg L − 1 ) and 13-cis β-carotene (2.62 mg L − 1 ), surpassing those found under BL and WL (Fig. 3 B). The variations in cellular contents of β-carotene and its cis isomers across BL, RL, and WL differed from those observed in algal liquids (Fig. 3 C). The content of all- trans β-carotene under BL was found to be the highest, measuring 1.48 pg cell − 1 . The cellular content of 9- cis β-carotene showed no significant differences between RL and WL, but was much higher under these two light qualities than under BL (0.23 pg cell − 1 ). Similarly, the accumulation pattern of 13- cis β-carotene in response to different light qualities was consistent with that of 9- cis β-carotene. The 13- cis β-carotene concentrations observed under RL and WL were 0.23 pg cell − 1 and 0.21 pg cell − 1 respectively, both greatly exceeding that observed under BL (0.13 pg cell − 1 ). These results indicate that BL is conducive to the accumulation of all- trans β-carotene in D. salina cells, whereas RL promotes the accumulation of both 9- cis and 13- cis β-carotenes in these cells. 3.5 Effects of light quality on gene expression in D. Salina Under GL, the growth of D. Salina cells is slow, and the light absorption and photosynthetic activity are weak. This indicates that GL cannot promote the growth of D. Salina cells in the green stage. Given that, only D. Salina cells cultivated under BL, RL, and WL were selected for non-reference transcriptomic analysis. In this study, a total of 9,187 differentially expressed genes (DEGs) were identified. The Venn diagram of transcriptomics shows that totally there are 7,968 genes exhibiting differential expression between the BL and RL treatment groups, between the BL and WL treatment groups, as well as between the RL and WL treatment groups. Notably, DEGs primarily occur between the BL and WL treatment groups, and between the RL and WL treatment groups. This suggests that the effects of RL and BL on gene expression in D. Salina are somewhat similar (Fig. 4 A). Figure 4 B reveals the differences in the number of DEGs among the treatment groups under varying light conditions, as well as their upregulation and downregulation. As shown in the bar chart, there are 8,256 DEGs between the RL and WL treatment groups, including 294 upregulated genes and 7,962 downregulated genes; between the BL and WL treatment groups, there are 8,745 DEGs, including 73 upregulated genes and 8,672 downregulated genes (Fig. 4 B). The KEGG pathway enrichment analysis demonstrates that the DEGs are primarily enriched in various metabolic processes, including the β-carotene biosynthesis pathway, sphingolipid metabolism pathway, steroid biosynthesis pathway, and fatty acid elongation pathway (Figs. 5 A and B). These findings suggest that RL and BL predominantly influence metabolism-related genes in D. Salina . 3.6 Effects of light quality on the expression of β-Carotene metabolic enzyme genes in D. salina The enzymes phytoene synthase ( PSY ), phytoene desaturase ( PDS ), ζ-carotene desaturase ( ZDS ), and lycopene β-cyclase ( LCYB ) play positive roles in the biosynthesis of β-carotene in plants (Amendola et al., 2023 ; Chen et al., 2023 ; Sathasivam and Ki, 2019 ; Lan et al., 2022 ). Among these, PSY is identified as the rate-limiting enzyme in the β-carotene biosynthetic pathway (Liang et al., 2023 ; Li et al., 2023 ). There were no significant differences observed in the relative expression levels of PSY , PDS and ZDS under BL, RL, and WL. However, LCYB reached the highest relative expression level under WL (Fig. 6 ).The enzymes β-hydroxylase ( LUT5 ), Zeaxanthin epoxidase ( ABA1 ), Abscisic acid dehydrogenase ( ABA2 ) play positive roles in the degradation of β-carotene in plants (Zhao et al., 2021 ; Jia et al., 2022 ; Tolnai et al., 2024 ). Compared to WL, the relative expression levels of LUT5 , ABA1 and ABA2 were prominently downregulated under BL; the relative expression levels of LUT5 and ABA2 were markly downregulated under RL, but the expression levels of ABA1 was upregulated under RL (Fig. 7 ). 4. Discussion Light quality is a crucial factor influencing the metabolism, growth, and reproduction of algal cells. Our research indicated that monochromatic light qualities can affect the light absorption characteristics and photosynthetic efficiency of D. Salina , and regulate the expression of key enzyme genes involved in the β-carotene biosynthesis pathway in D. Salina. Under BL, algal cells had the highest growth rate (Fig. 1 A, B). Additionally, the bioconversion pathway from β-carotene to abscisic acid was significantly inhibited under BL (Fig. 7 ), which thus reduced the degradation of β-carotene and facilitated its accumulation within algal cells. Previous studies showed that strong light stress can lead to the accumulation of carotenoids in D. Salina cells (Ye et al., 2008 ). However, our study featured an average light intensity of 40 µmol photons m − 2 s − 1 , which is insufficient to induce photoinhibition in D. Salina cells (Sui et al., 2019 ; Capa-Robles et al., 2021 ; Kim et al., 2024 ). Therefore, the differences in the cell density and specific growth rate of D. Salina are primarily attributed to variations in light quality. Our results indicate that the specific growth rate under BL is slightly higher than those under RL and WL, and significantly higher than that under GL (Fig. 1 A, B). Thus, for microalgal cultivation, BL and RL irradiation are considered efficient, while GL irradiation is regarded as less effective (Wagner et al., 2016 ). Table 2 shows that a portion of incident light is absorbed by the cells across four different light qualities (ranging from 22.1–37.9%). The absorption by pigments is slightly lower than that by the cells themselves, ranging from 10.2–22.8%. Supporting Information: Figure S2 and S3 indicated that there were no significant differences in cell size among the D. Salina cultures under different light qualities. In light of that, the disparities observed in cellular and pigment absorption rates across various wavelengths cannot be attributed to differences in algal cell size. Rather, they reflect variations in absorption capabilities of D. Salina cells and pigments with different spectral bands. Among the light qualities involved in our study, BL and RL provide the highest and second highest pigment-level absorption rates, respectively (22.8% and 18.6%), whereas GL has a lower pigment-level absorption rate, no more than 10.2%. The discrepancies between cellular and pigment-level absorptive capacities effectively represent variations in pigment content of D. Salina under different light qualities (Table 2 ). This finding aligns with our earlier observations on other species of Dunaliella sp. such as Dunaliella sp. MACC/C43 (Li et al., 2020b ). We further hypothesize that RL offers the highest effective absorption rate, approximately 81.8%, which helps maintain a balance between algal cell photoabsorption and utilization efficiency. This allows for sustained high photosynthetic activity even at lower chlorophyll levels within cells. However, both photoabsorption by algal cells (Table 2 ) and the efficiency of energy utilization by RCs under RL do not match those achieved under BL. As a result, the cell proliferation rate and pigment content under RL are lower than those under BL. In cells, chloroplasts containing pigments exist within a complex molecular environment. Other cellular components, such as proteins, carbohydrates, and lipids, have distinct optical properties that can diminish the light energy reaching PSII reaction centers of algal cells (Johnsen and Sakshaug, 2007 ; Lehmuskero et al., 2017). Light quality strongly influences both pigment content and composition in D. Salina cells (Figs. 1 C, D; Fig. 3 ). In this study, the ratio of light-harvesting antenna pigments to reaction center pigments in D. Salina under BL are significantly different to those under the other light qualities (Fig. 3 A). This finding is consistent with previous studies (Gorai et al., 2014 ; Li and Liu, 2020 ). Therefore, a logical explanation is that exposure to monochromatic light may play an active role in pigment synthesis. The ratio of light-harvesting pigments (Chl-b + Car) to antenna pigments (Chl-a) is considered indicative of the photonic capture capability of a PSII reaction center (Ueno et al., 2019 ). The ratio of light-harvesting pigments to reaction center pigments under BL is significantly higher than those under the other light qualities (Fig. 3 A), facilitating enhanced capture and absorption of light energy. This observation is corroborated by the results concerning chlorophyll fluorescence transients (Fig. 2 ). Similarly, the elevated values of F V /Fm, Pi-ABS, ABS/RC, TR 0 /RC, ET 0 /RC, and 1-V J under BL indicate improvements in the efficiency of the photosynthetic electron transport chain and the photosynthetic capacity of algal cells as a result of BL exposure (Fig. 2 ). Furthermore, the increased DI 0 /RC value under GL suggests a rise in thermal dissipation at PSII reaction centers of D. Salina and a reduction in the rate of electron transfer from Q A to Q B during GL exposure. In conclusion, we propose that light intensity being low, D. Salina cells are more effective at absorbing and transferring light energy to PSII under BL than under other light qualities. Thus, carbon assimilation processes within these cells are more efficient under BL, resulting in higher photosynthetic efficiency and growth rates. Conversely, under GL, a greater portion of absorbed light energy is dissipated at PSII reaction centers to reduce both the rate of photosynthetic electron transport and overall photosynthetic efficiency. This is how the pigment content of D. Salina cells lowers and their growth slows down under GL. Based on the abovementioned proposal, we developed a model to explain how halophytic algae maintain a balance between light absorption and energy utilization under different light qualities (Fig. 8 ). The results of qPCR (Fig. 6 ) further support our inference. Specifically, there were no significant differences in the expression levels of key enzyme genes involved in the β-carotene synthesis pathway—such as PSY , PSD , ZDS —in D. Salina cells under varying light qualities (BL, WL, and RL) (Fig. 6 ). Song et al. ( 2023 ) found that the expression of LCYB is upregulated under far red light. We speculate that the expression of LCYB may be regulated by the spectral range of light, and monochromatic light (i.e.,BL, RL, and GL) may downregulate the expression level of LCYB. This is why the upregulation of LCYB gene expression under WL is observed in D. salina. Therefore, we can infer that the expression levels of these key enzyme genes exert no influence on β-carotene content within D. Salina cells. This indicates that the differences in β-carotene synthesis capacity among D. Salina cells under different light qualities are attributed to variations in these cells’ capability to absorb and utilize light energy. Figures 3 C and D indicate that monochromatic RL and BL, compared to WL, can increase the content and activity of β-carotene and its cis-isomers in algal cultures. This phenomenon has been reported in several previous studies (Sui et al., 2021 ; Mohebi-Najafabadi and Naeimpoor, 2023; Mirzaie et al., 2021 ). However, the mechanisms underlying the effects of light qualities on β-carotene accumulation in D. Salina remain unclear. In this study, we performed qPCR and transcriptomic analysis to assess gene expression in D. Salina under different light qualities. The influence of RL and BL on gene expression was largely similar: as illustrated by the Venn diagram, there are 7,848 genes co-affected by RL and BL (Fig. 4 A). Notably, most of these affected genes were downregulated (Fig. 4 B), characterized by a great concentration among metabolism-related pathways. Furthermore, four differentially expressed genes (DEGs) were identified within the β-carotene biosynthetic pathway (Figs. 5 A and B). Our findings further demonstrate that monochromatic BL exerts a more pronounced effect on the metabolic pathway genes associated with β-carotene in D. Salina (Fig. 7 ). This study employed qPCR to measure the expression levels of PSY , PDS , ZDS , and LCYB in D. Salina under different light qualities, as a step to investigate the influence of light qualities on the β-carotene synthesis pathway. The transcriptomic analysis revealed that four differentially expressed genes (DEGs) were primarily enriched in the carotenoid metabolism pathway. To elucidate the differences in gene expression related to carotenoid synthesis and degradation pathways under varying light, we built two models (Figs. 6 and 7 ). Figure 6 illustrates that there are no significant differences in the relative expression levels of PSY , PDS , and ZDS among BL, RL, and WL; however, under GL, their relative expression levels were significantly higher than those observed under other light qualities. We hypothesize that this increase in PSY , PDS , and ZDS expression may be associated with a negative feedback regulation mechanism employed by D. Salina cells to dissipate excess light energy. Amid GL exposure where D. Salina cells utilize light inefficiently, carotenoids can serve as structural and functional pigments within the photocomplexes involved in non-photochemical quenching (Dall'Osto et al., 2006 ). PSII reaction centers of microalgae dissipate excess light energy primarily through both photochemical quenching and non-photochemical quenching pathways (Crepin and Caffarri, 2018 ). In order to mitigate excess light energy during GL exposure, algae cells upregulate the expression of genes such as PSY , PDS , and ZDS to synthesize more carotenoids as a means of non-photochemical quenching. The elevated DI 0 /RC ratio observed under GL further supports this inference. Xu and Harvey ( 2019 ) compared the ratios of all- trans β-carotene to 9- cis β-carotene in Dunaliella salina under monochromatic RL and BL. They found that RL upregulates the activity of 9- cis -βC-ISO, an enzyme converting all- trans β-carotene into its cis isomers. They hypothesized that under RL, D. salina enhances the synthesis of 9- cis β-carotene to rapidly expand its antioxidant pool, thus reducing the formation rate of reactive oxygen species (ROS). Similarly, we observed that under RL, D. salina cells synthesized higher levels of cis isomers (including 9- cis and 13- cis β-carotene), while under BL, there was a greater accumulation of all- trans β-carotene (Fig. 3 ). Ben-Amotz et al. ( 1989 ) reported significant photoinhibition in D. salina cells exposed to high-intensity RL, which led to substantial production of ROS. The mechanism Xu and Harvey proposed for ROS clearance may be one reason why a higher proportion of cis isomeric forms occurs under RL than under BL. Interestingly, we found that the differences in β-carotene content under different light qualities are associated with not only the upstream synthesis but also the downstream degradation in the β-carotene metabolic pathway. Abscisic acid ( ABA ) is a plant hormone derived from carotenoid precursors. Its biosynthesis begins with the conversion of all- trans β-carotene to 9- cis β-carotene, which serves as a direct precursor (Tolnai et al., 2024 ). Figure 7 illustrates that the massive accumulation of β-carotene under RL and BL is attributed to their capability to markedly downregulate the genes related to β-carotene degradation (LUT5 , ABA2 ). Under RL and BL, the metabolic pathway from β-carotene to ABA is significantly inhibited, thereby reducing both the degradation and loss of β-carotene. Notably, while ABA1 gene expression is significantly downregulated under BL, it undergoes a marked upregulation under RL. Research by Barrero et al. ( 2008 ) indicates that ABA1 gene expression is influenced by light intensity, and tends to be downregulated in strong light and upregulated in weak light or darkness. We propose that this may relate to the attenuation levels of RL and BL in aquatic environments: RL attenuates more rapidly than BL does (Siefermann-Harms, 1987 ). Consequently, a significant difference exists in ABA1 gene expression within D. salina cells under RL and BL of the same intensity. Furthermore, LUT5 and ABA2 undergo greater downregulation under BL than under RL, indicating that BL exerts a stronger inhibitory effect on β-carotene metabolism than RL does. In this way, all- trans β-carotene is prevented from converting into its biosynthetic precursor for ABA (9- cis -β-carotene). The conversion process is suppressed more effectively under BL than under RL. As such, we observed an overall downregulation of the β-carotene metabolism pathway within D. salina cells under BL—this accounts for their higher content of all- trans β-carotene under BL. Ultimately, through Fig. 7 , at the level of differential gene expression, we elucidate the mechanisms underlying substantial accumulation and activity variations ofβ-carotenoids induced by exposure to differing wavelengths of illumination, in D. salina cells. 5. Conclusion Light quality can regulate photosynthetic electron transport activity and gene expression in the β-carotene metabolism pathways in D. salina . Ultimately, this regulation affects the growth of D. salina , the accumulation of β-carotene, and the proportions of its cis isomers, namely 9- cis carotene, 13- cis carotene, and all- trans β-carotene. Compared to WL, monochromatic BL and monochromatic RL are more conducive to the accumulation of β-carotene in algae cells. Under BL, the content of all- trans β-carotene is much higher, while under RL, the contents of 9- cis carotene and 13- cis carotene are elevated. Both BL and RL enhance the algal cells' capability to absorb light, increase the rate of photosynthetic electron transport, and reduce energy dissipation, thereby improving cellular photosynthetic efficiency and activity. Such effects help promote the energy conversion processes within algal cells, facilitating the synthesis and accumulation of carotenoids. Light quality can regulate the accumulation of β-carotene in D. salina and its cis-isomerization levels. This is associated with both the upstream synthesis of β-carotene and the downstream degradation related to its conversion into abscisic acid ( ABA ). Two key genes involved in the β-carotene degradation pathway , LUT5 and ABA2 , are significantly downregulated under BL and RL, resulting in a reduced breakdown of carotenoids within cells. The conversion from all- trans β-carotene to the ABA biosynthetic precursor 9- cis β-carotene is significantly inhibited under BL, leading to a higher degree of suppression in β-carotene metabolism. This explains why D. salina produces a greater content of all- trans β-carotene when exposed to BL. Declarations Credit authorship contribution statement Tianze Zhao: Conceptualization, Supervision, Validation, Writing - review. Yongfu Li: Conceptualization, Investigation, Data curation. Xingkai Che: Investigation. Haixing Wu: Writing - editing. Yuchen Ye: Methodology. Dingning Fan: Software. Zhendong Li: Methodology. Yingjie Zhao: Methodology. Wei Ye: Methodology. Statement of informed consent, human/animal rights No conflicts, informed consent, human or animal rights applicable. Declaration of author agreement to authorship and submission All the authors declare that this manuscript is original, has not been published before, and is not currently being considered for publication elsewhere. All authors have approved the manuscript and agreed with its submission to the Ecotoxicology and Environmental Safety Declaration of competing interest The authors have no conflict of interest. We claim that we have no commercial or associative interest relevant to the work that contributes to conflict of interest. Funding This work was supported by the Fundamental Research Funds for the Central Universities (B240201165), the National Natural Science Foundation of China (No. 42276189), the GEF Small Grants Programme China (CPR/DLF/IW/2023/03), the National Nonprofit Institute Research Grants of TIWTE (TKS20230304), and the Innovation and Entrepreneurship project for college students of Hohai University (202310294184Y). Availability of data and materials Data and materials will be made available on request. References Amendola, S., Kneip, J. S., Meyer, F., Perozeni, F., Cazzaniga, S., Lauersen, K. J., Baier, T. (2023). Metabolic engineering for efficient ketocarotenoid accumulation in the green microalga Chlamydomonas reinhardtii . ACS Synthetic Biology , 12(3) , 820-831. Arnon, D. I. (1949). Copper enzymes in isolated chloroplasts. Polyphenoloxidase in Beta vulgaris. Plant physiology , 24(1) , 1. Barrero, J. M., Rodríguez, P. L., Quesada, V., AlabadI, D., Blazquez, M. A., BOUTIN, J. P., Micol, J. L. (2008). The ABA1 gene and carotenoid biosynthesis are required for late skotomorphogenic growth in Arabidopsis thaliana . Plant, cell & environment , 31(2) , 227-234. Ben-Amotz, A. (1995). New mode of Dunaliella biotechnology: two-phase growth for β-carotene production. Journal of applied phycology , 7 , 65-68. Ben-Amotz, A., Shaish, A., Avron, M. (1989). Mode of action of the massively accumulated β-carotene of Dunaliella bardawil in protecting the alga against damage by excess irradiation. Plant Physiology , 91(3) , 1040-1043. Borowitzka, L. J., Borowitzka, M. A. (1989). β-carotene (provitamin A) production with algae. In Biotechnology of vitamins, pigments and growth factors (pp. 15-26). Dordrecht: Springer Netherlands. Borowitzka, M. A. (1988). Algal growth media and sources of algal cultures. In Micro-algal biotechnology (pp. 456-465). Cambridge University Press. Borowitzka, M. A. (2013). Dunaliella: biology, production, and markets. Handbook of microalgal culture: applied phycology and biotechnology , 359-368. Bustin, S. A., Beaulieu, J. F., Huggett, J., Jaggi, R., Kibenge, F. S., Olsvik, P. A., Toegel, S. (2010). MIQE precis: Practical implementation of minimum standard guidelines for fluorescence-based quantitative real-time PCR experiments. BMC molecular biology , 11(1) , 1-5. Capa-Robles, W., García-Mendoza, E., Paniagua-Michel, J. D. J. (2021). Enhanced β-carotene and biomass production by induced mixotrophy in Dunaliella salina across a combined strategy of glycerol, salinity, and light. Metabolites , 11(12) , 866. Chen, C. Y., Chen, Y. C., Huang, H. C., Ho, S. H., Chang, J. S. (2015). Enhancing the production of eicosapentaenoic acid (EPA) from Nannochloropsis oceanica CY2 using innovative photobioreactors with optimal light source arrangements. Bioresource technology , 191 , 407-413. Chen, C. Y., Yeh, K. L., Aisyah, R., Lee, D. J., Chang, J. S. (2011). Cultivation, photobioreactor design and harvesting of microalgae for biodiesel production: a critical review. Bioresource technology , 102(1) , 71-81. Chen, H. H., Liang, M. H., Ye, Z. W., Zhu, Y. H., Jiang, J. G. (2023). Engineering the β-carotene metabolic pathway of microalgae Dunaliella to confirm its carotenoid synthesis pattern in comparison to bacteria and plants. Microbiology Spectrum , 11(2) , e04361-22. Chen, X., Khadiwada, J. R., Chio, C., Shrestha, S., Kognou, A. L. M., Fan, L., Qin, W. (2024). Low-cost cultivation of Nannochloropsis oceanica in newly designed photobioreactors and its productivity trends in semi-continuous cultivation under inland outdoor conditions. Bioresource Technology , 402 , 130829. Crepin, A., Caffarri, S. (2018). Functions and evolution of Lhcb isoforms composing LHCII, the major light harvesting complex of photosystem II of green eukaryotic organisms. Current Protein and Peptide Science , 19(7) , 699-713. Dall'Osto, L., Lico, C., Alric, J., Giuliano, G., Havaux, M., Bassi, R. (2006). Lutein is needed for efficient chlorophyll triplet quenching in the major LHCII antenna complex of higher plants and effective photoprotection in vivo under strong light. BMC plant biology , 6 , 1-20. Danesh, A. F., Ebrahimi, S., Salehi, A., Parsa, A. (2017). Impact of nutrient starvation on intracellular biochemicals and calorific value of mixed microalgae. Biochemical Engineering Journal , 125 , 56-64. Del-Campo, J. A., García-González, M., Guerrero, M. G. (2007). Outdoor cultivation of microalgae for carotenoid production: current state and perspectives. Applied microbiology and biotechnology , 74 , 1163-1174. Díaz, J. P., Inostroza, C., Acién, F. G. (2021). Scale-up of a Fibonacci-Type Photobioreactor for the Production of Dunaliella salina . Applied Biochemistry and Biotechnology , 193 , 188-204. Fiedor, J., Burda, K. (2014). Potential role of carotenoids as antioxidants in human health and disease. Nutrients , 6(2) , 466-488. Fu, W., Guðmundsson, Ó., Paglia, G., Herjólfsson, G., Andrésson, Ó. S., Palsson, B. Ø., Brynjólfsson, S. (2013). Enhancement of carotenoid biosynthesis in the green microalga Dunaliella salina with light-emitting diodes and adaptive laboratory evolution. Applied microbiology and biotechnology , 97 , 2395-2403. Gómez, P. I., González, M. A. (2005). The effect of temperature and irradiance on the growth and carotenogenic capacity of seven strains of Dunaliella salina (Chlorophyta) cultivated under laboratory conditions. Biological research , 38(2-3) , 151-162. Gorai, T., Katayama, T., Obata, M., Murata, A., Taguchi, S. (2014). Low blue light enhances growth rate, light absorption, and photosynthetic characteristics of four marine phytoplankton species. Journal of experimental marine biology and ecology , 459 , 87-95. Götz, T., Windhövel, U., Böger, P., Sandmann, G. (1999). Protection of photosynthesis against ultraviolet-B radiation by carotenoids in transformants of the cyanobacterium Synechococcus PCC7942. Plant Physiology , 120(2) , 599-604. Greenberger, S., Harats, D., Salameh, F., Lubish, T., Harari, A., Trau, H., Shaish, A. (2012). 9-cis–rich β-carotene powder of the alga Dunaliella reduces the severity of chronic plaque psoriasis: a randomized, double-blind, placebo-controlled clinical trial. Journal of the American College of Nutrition , 31(5) , 320-326. Grune, T., Lietz, G., Palou, A., Ross, A. C., Stahl, W., Tang, G., Biesalski, H. K. (2010). β-Carotene is an important vitamin A source for humans. The Journal of nutrition , 140(12) , 2268S-2285S. Guermazi, W., Masmoudi, S., Trabelsi, N. A., Gammoudi, S., Ayadi, H., Morant-Manceau, A., Hotos, G. N. (2023). Physiological and biochemical responses in microalgae Dunaliella salina , Cylindrotheca closterium and Phormidium versicolor NCC466 exposed to high salinity and irradiation. Life , 13(2) , 313. Harari, A., Harats, D., Marko, D., Cohen, H., Barshack, I., Gonen, A., Shaish, A. (2013). Supplementation with 9-cis β-carotene-rich alga Dunaliella improves hyperglycemia and adipose tissue inflammation in diabetic mice. Journal of applied phycology , 25 , 687-693. Harvey, P. J., Ben-Amotz, A. (2020). Towards a sustainable Dunaliella salina microalgal biorefinery for 9-cis β-carotene production. Algal Research , 50 , 102002. Hejazi, M. A., Holwerda, E., Wijffels, R. H. (2004). Milking microalga Dunaliella salina for β‐carotene production in two‐phase bioreactors. Biotechnology and bioengineering , 85(5) , 475-481. Honda, M. (2021). Carotenoid isomers: A systematic review of the analysis, biological activity, physicochemical property, and methods for isomerization. Studies in natural products chemistry , 68 , 173-220. Huang, Z., Zong, M. H., Wang, J., Peng, S. Y., Yu, M., Lou, W. Y. (2024). Structural and interfacial properties of acetylated Millettia speciosa Champ polysaccharide and stability evaluation of the resultant O/W emulsion containing β-carotene. International Journal of Biological Macromolecules , 264 , 130556. Jia, K. P., Mi, J., Ali, S., Ohyanagi, H., Moreno, J. C., Ablazov, A., Al-Babili, S. (2022). An alternative, zeaxanthin epoxidase-independent abscisic acid biosynthetic pathway in plants. Molecular Plant , 15(1) , 151-166. Johnsen, G., Sakshaug, E. (2007). Biooptical characteristics of PSII and PSI in 33 species (13 pigment groups) of marine phytoplankton, and the relevance for pulse‐amplitude‐modulated and fast‐repetition‐rate fluorometry 1. Journal of Phycology , 43(6) , 1236-1251. Kevin, K., Widjaja, A. (2023). Effect of nitrogen deficiency and UV light on Dunaliella salina β-carotene production. In AIP Conference Proceedings (Vol. 2847, No. 1). AIP Publishing. Kim, M., Kim, J., Lee, S., Khanh, N., Li, Z., Polle, J. E., Jin, E. (2024). Deciphering the β‐carotene hyperaccumulation in Dunaliella by the comprehensive analysis of Dunaliella salina and Dunaliella tertiolecta under high light conditions. Plant, Cell & Environment , 47(1) , 213-229. Lam, M. K., Lee, K. T. (2014). Scale-up and commercialization of algal cultivation and biofuel production. Biofuels from algae . Elsevier, Amsterdam, pp 261-286. Lamers, P. P., van de Laak, C. C., Kaasenbrood, P. S., Lorier, J., Janssen, M., De Vos, R. C., Wijffels, R. H. (2010). Carotenoid and fatty acid metabolism in light‐stressed Dunaliella salina . Biotechnology and bioengineering , 106(4) , 638-648. Lan, Y., Song, Y., Guo, Y., Qiao, D., Cao, Y., Xu, H. (2022). DsLCYB Directionally Modulated β-Carotene of the Green Alga Dunaliella salina under Red Light Stress. Journal of Microbiology and Biotechnology , 32(12) , 1622. Lehmuskero, A., Chauton, M. S., Boström, T. (2018). Light and photosynthetic microalgae: A review of cellular-and molecular-scale optical processes. Progress in oceanography , 168 , 43-56. Leo, M. A., Lieber, C. S. (1999). Alcohol, vitamin A, and β-carotene: adverse interactions, including hepatotoxicity and carcinogenicity. The American journal of clinical nutrition , 69(6) , 1071-1085. Li, J. W., Zhou, P., Deng, Y. J., Hu, Z. H., Li, X. H., Chen, X., Zhuang, J. (2023). Overexpressing CsPSY1 Gene of Tea Plant, Encoding a Phytoene Synthase, Improves α-Carotene and β-Carotene Contents in Carrot. Molecular Biotechnology , 1-12. Li, Y. F., Meng, F. P. (2014). Type selection of transparent plate for microalgae photo-bioreactor building based on light transmissivity analysis. Acta Opt Sin , 1 , 0123003-0123006. Li, Y., Cai, X., Gu, W., Wang, G. (2020a). Transcriptome analysis of carotenoid biosynthesis in Dunaliella salina under red and blue light. Journal of Oceanology and Limnology , 38(1) , 177-185. Li, Y., Li, L., Liu, J., Qin, R. (2020b). Light absorption and growth response of Dunaliella under different light qualities. Journal of applied phycology , 32 , 1041-1052. Li, Y., Liu, J. (2020). Analysis of light absorption and photosynthetic activity by Isochrysis galbana under different light qualities. Aquaculture research , 51(7) , 2893-2902. Li, Y., Zhao, T., Qin, M., Che, X., Zhang, A. (2024). Toxicity of the sunscreen UV filter benzophenone-3 (OBZ) to the microalga Selenastrum capricornutum : An insight into OBZ’s damage to photosynthesis and respiration. Ecotoxicology and Environmental Safety , 278 , 116441. Liang, M. H., Xie, S. R., Dai, J. L., Chen, H. H., Jiang, J. G. (2023). Roles of two phytoene synthases and orange protein in carotenoid metabolism of the β-carotene-accumulating Dunaliella salina . Microbiology Spectrum , 11(3) , e00069-23. Lima, S., Schulze, P. S., Schüler, L. M., Rautenberger, R., Morales-Sánchez, D., Santos, T. F., Kiron, V. (2021). Flashing light emitting diodes (LEDs) induce proteins, polyunsaturated fatty acids and pigments in three microalgae. Journal of Biotechnology , 325 , 15-24. Ma, C., Qu, W., Ho, S. H., Li, J., Li, F., Yi, L. (2024). Effects of microalgal ( Tetradesmus obliquus MCX38) attachment on photobioreactor treatment efficiency of raw swine wastewater. Bioresource Technology , 403 , 130866. Mazzucchi, L., Xu, Y., Harvey, P. (2020). Stereoisomers of colourless carotenoids from the marine microalga Dunaliella salina . Molecules , 25(8) , 1880. Mirzaie, M. M., Lak, Z. J., Meybodi, F. H. (2021). A new shifting strategy in flashing light based on the cell growth curve to enhance β-carotene biosynthesis in Dunaliella salina . Current Microbiology , 78(7) , 2733-2740. Mizobuchi, K., Hayashi, T., Ueno, S., Kondo, M., Terasaki, H., Aoki, T., Nakano, T. (2023). One-Year Outcomes of Oral Treatment With Alga Capsules Containing Low Levels of 9-cis-β-Carotene in RDH5-Related Fundus Albipunctatus. American Journal of Ophthalmology , 254 , 193-202. Mohebi Najafabadi, M., Naeimpoor, F. (2023). Boosting β-carotene and storage materials productivities by two-stage mixed and monochromatic exposure stresses on Dunaliella salina . International Journal of Phytoremediation , 25(5), 609-620. Moheimani, N. R., Parlevliet, D. (2013). Sustainable solar energy conversion to chemical and electrical energy. Renewable and Sustainable Energy Reviews , 27 , 494-504. Molina-Miras, A., López-Rosales, L., Sánchez-Mirón, A., Cerón-García, M. C., Seoane-Parra, S., García-Camacho, F., Molina-Grima, E. (2018). Long-term culture of the marine dinoflagellate microalga Amphidinium carterae in an indoor LED-lighted raceway photobioreactor: Production of carotenoids and fatty acids. Bioresource technology , 265 , 257-267. Murthy, K. C., Vanitha, A., Rajesha, J., Swamy, M. M., Sowmya, P. R., Ravishankar, G. A. (2005). In vivo antioxidant activity of carotenoids from Dunaliella salina —a green microalga. Life sciences , 76(12) , 1381-1390. National Standardization Technical Committee (2008) Standard illuminants and geometric conditions GB/T 3978-2008. China Standard Press , Beijing. Papaioannou, E. H., Liakopoulou-Kyriakides, M. (2012). Agro-food wastes utilization by Blakeslea trispora for carotenoids production. Acta Biochimica Polonica , 59(1) , 151-153. Prieto, A., Cañavate, J. P., García-González, M. (2011). Assessment of carotenoid production by Dunaliella salina in different culture systems and operation regimes. Journal of biotechnology , 151(2) , 180-185. Priscilla, K., Sharma, V., Gautam, A., Gupta, P., Dagar, R., Kishore, V., Kumar, R. (2024). Carotenoid Extraction from Plant Tissues. In Plant Functional Genomics: Methods and Protocols , Volume 2 (pp. 3-18). New York, NY: Springer US. Pulz, O., Gross, W. (2004). Valuable products from biotechnology of microalgae. Applied microbiology and biotechnology , 65 , 635-648. Qin, R., Li, Y., Zhang, L., Liu, J. (2021). The effect of salinity shock on the growth and rapid light curve of D unaliella salina . Aquaculture Research , 52(6) , 2569-2579. Rasband, W. S. (2012). ImageJ: Image processing and analysis in Java. Astrophysics Source Code Library , ascl-1206. Relevy, N. Z., Rühl, R., Harari, A., Grosskopf, I., Barshack, I., Ben-Amotz, A., Shaish, A. (2015). 9-cis β-Carotene inhibits atherosclerosis development in female LDLR-/-mice. Functional Foods in Health and Disease , 5(2) , 67-79. Rodríguez-Bolaños, M., Vargas-Romero, G., Jaguer-García, G., Aguilar-Gonzalez, Z. I., Lagos-Romero, V., Miranda-Astudillo, H. V. (2024). Antares I: a Modular Photobioreactor Suitable for Photosynthesis and Bioenergetics Research. Applied Biochemistry and Biotechnology , 196(4) , 2176-2195. Rozenberg, J. M., Sorokin, B. A., Mukhambetova, A. N., Emelianova, A. A., Kuzmin, V. V., Belogurova‐Ovchinnikova, O. Y., Kuzmin, D. V. (2024). Recent advances and fundamentals of microalgae cultivation technology. Biotechnology Journal , 19(3) , 2300725. Sathasivam, R., Ki, J. S. (2019). Differential transcriptional responses of carotenoid biosynthesis genes in the marine green alga Tetraselmis suecica exposed to redox and non-redox active metals. Molecular biology reports , 46(1) , 1167-1179. Siefermann‐Harms, D. (1987). The light‐harvesting and protective functions of carotenoids in photosynthetic membranes. Physiologia Plantarum , 69(3) , 561-568. Song, Y., Teakle, G., Lillywhite, R. (2023). Unravelling effects of red/far-red light on nutritional quality and the role and mechanism in regulating lycopene synthesis in postharvest cherry tomatoes. Food Chemistry , 414 , 135690. Strasser, B., Strasser, R. (1995). Measuring fast fluorescence transients to address environmental questions: The JIP test. In Photosynthesis: From Light to Biosphere (Edited by P. Mathis), pp. 977-980. Kluwer Academic , Dordrecht . Sui, Y., Mazzucchi, L., Acharya, P., Xu, Y., Morgan, G., Harvey, P. J. (2021). A Comparison of β-Carotene, Phytoene and Amino Acids Production in Dunaliella salina DF 15 (CCAP 19/41) and Dunaliella salina CCAP 19/30 Using Different Light Wavelengths. Foods , 10(11) , 2824. Sui, Y., Muys, M., Van de Waal, D. B., D'Adamo, S., Vermeir, P., Fernandes, T. V., Vlaeminck, S. E. (2019). Enhancement of co-production of nutritional protein and carotenoids in Dunaliella salina using a two-phase cultivation assisted by nitrogen level and light intensity. Bioresource technology , 287 , 121398. Tolnai, Z., Sharma, H., Soós, V. (2024). D27-like carotenoid isomerases: at the crossroads of strigolactone and abscisic acid biosynthesis. Journal of Experimental Botany , 75(4) , 1148-1158. Tredici, M. R. (2004). Mass production of microalgae: photobioreactors. Handbook of microalgal culture: Biotechnology and applied phycology , 1 , 178-214. Ueno, Y., Aikawa, S., Kondo, A., Akimoto, S. (2019). Adaptation of light-harvesting functions of unicellular green algae to different light qualities. Photosynthesis research , 139 , 145-154. Wagner, I., Steinweg, C., Posten, C. (2016). Mono‐and dichromatic LED illumination leads to enhanced growth and energy conversion for high‐efficiency cultivation of microalgae for application in space. Biotechnology journal , 11(8) , 1060-1071. Wang, X. D., Krinsky, N. I., Benotti, P. N., Russell, R. M. (1994). Biosynthesis of 9-cis-retinoic acid from 9-cis-β-carotene in human intestinal mucosa in vitro . Archives of Biochemistry and Biophysics , 313(1) , 150-155. Wang, Z., Gerstein, M., Snyder, M. (2009). RNA-Seq: a revolutionary tool for transcriptomics. Nature reviews genetics , 10(1) , 57-63. Xi, Y., Xue, S., Cao, X., Chi, Z., Wang, J. (2021). Quantitative analysis on photon numbers received per cell for triggering β-carotene accumulation in Dunaliella salina . Bioresources and Bioprocessing , 8 , 1-11. Xu, Y., Harvey, P. J. (2019). Red light control of β-carotene isomerisation to 9-cis β-carotene and carotenoid accumulation in Dunaliella salina . Antioxidants , 8(5) , 148. Ye, Z. W., Jiang, J. G., Wu, G. H. (2008). Biosynthesis and regulation of carotenoids in Dunaliella: progresses and prospects. Biotechnology advances , 26(4) , 352-360. Zhao, Y., Wang, J., Zhang, H., Yan, C., Zhang, Y. (2013). Effects of various LED light wavelengths and intensities on microalgae-based simultaneous biogas upgrading and digestate nutrient reduction process. Bioresource technology , 136 , 461-468. Zhao, Y., Yang, X., Hu, Y., Gu, Q., Chen, W., Li, J., Liu, Y. (2021). Evaluation of carotenoids accumulation and biosynthesis in two genotypes of pomelo (Citrus maxima) during early fruit development. Molecules , 26(16) , 5054. Additional Declarations No competing interests reported. Supplementary Files SupportingInformation.pdf Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 29 Jan, 2025 Reviews received at journal 27 Jan, 2025 Reviewers agreed at journal 06 Jan, 2025 Reviews received at journal 02 Jan, 2025 Reviewers agreed at journal 05 Dec, 2024 Reviewers invited by journal 18 Nov, 2024 Editor assigned by journal 17 Nov, 2024 Submission checks completed at journal 17 Nov, 2024 First submitted to journal 13 Nov, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5450150","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":386605816,"identity":"447894ea-d865-4df1-a19f-e0b46e668d02","order_by":0,"name":"Tianze Zhao","email":"","orcid":"","institution":"Hohai University","correspondingAuthor":false,"prefix":"","firstName":"Tianze","middleName":"","lastName":"Zhao","suffix":""},{"id":386605817,"identity":"229ac70b-9746-4563-9467-acaac4bd53dc","order_by":1,"name":"Yongfu Li","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA1ElEQVRIiWNgGAWjYBACPmYwJcfAL8EDYjAT1sIGUWPMIDmDaC0MUC0GN4jWws5j+Ljgl0Hi5tu9xyQYKqwTG9jPHiDgMB5j45l9Bonb7pxLk2A4k57YwJOXQEiLmTRvz5/EbTdyzCQY2w4nNkjwGBCjBeiwGSAt/4jVwvPDIHGDBEhLA1Fa2IqNeRsMjGfcyDG2SDiWbtzGk4NfCz//4Y2Pef4YyPbPyDG88aHGWraf/Qx+LQwMHAYMjG1QdgIDPKbwAfYHDAx/CCsbBaNgFIyCEQwADzc7Pbqm6eoAAAAASUVORK5CYII=","orcid":"","institution":"Hohai University","correspondingAuthor":true,"prefix":"","firstName":"Yongfu","middleName":"","lastName":"Li","suffix":""},{"id":386605819,"identity":"022732d4-ad84-429e-ab23-4afa0b91c3db","order_by":2,"name":"Xingkai Che","email":"","orcid":"","institution":"Hohai University","correspondingAuthor":false,"prefix":"","firstName":"Xingkai","middleName":"","lastName":"Che","suffix":""},{"id":386605820,"identity":"418b6f30-8536-462a-8e74-1696b943bf60","order_by":3,"name":"Haixing Wu","email":"","orcid":"","institution":"Hohai University","correspondingAuthor":false,"prefix":"","firstName":"Haixing","middleName":"","lastName":"Wu","suffix":""},{"id":386605821,"identity":"a3522cb5-0e24-44fe-a01d-283434e9d06f","order_by":4,"name":"Yuchen Ye","email":"","orcid":"","institution":"Hohai University","correspondingAuthor":false,"prefix":"","firstName":"Yuchen","middleName":"","lastName":"Ye","suffix":""},{"id":386605823,"identity":"ba2fa320-fde5-47bf-8c45-bac0de0d76e7","order_by":5,"name":"Dingning Fan","email":"","orcid":"","institution":"Hohai University","correspondingAuthor":false,"prefix":"","firstName":"Dingning","middleName":"","lastName":"Fan","suffix":""},{"id":386605825,"identity":"684a980f-7635-4ff1-ae2e-712ec31af4e9","order_by":6,"name":"Zhendong Li","email":"","orcid":"","institution":"Tianjin Research Institute of Water Transport Engineering","correspondingAuthor":false,"prefix":"","firstName":"Zhendong","middleName":"","lastName":"Li","suffix":""},{"id":386605826,"identity":"92935ee7-4191-422d-af00-c7373ab5766c","order_by":7,"name":"Yingjie Zhao","email":"","orcid":"","institution":"Tianjin Research Institute of Water Transport Engineering","correspondingAuthor":false,"prefix":"","firstName":"Yingjie","middleName":"","lastName":"Zhao","suffix":""},{"id":386605828,"identity":"cb4528da-aa49-4f97-88e6-9d24269a6e5d","order_by":8,"name":"Wei Ye","email":"","orcid":"","institution":"Tianjin Research Institute of Water Transport Engineering","correspondingAuthor":false,"prefix":"","firstName":"Wei","middleName":"","lastName":"Ye","suffix":""}],"badges":[],"createdAt":"2024-11-14 01:53:24","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5450150/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5450150/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":71783064,"identity":"f0a82cb5-6164-4eca-b9c1-ec335b0ac171","added_by":"auto","created_at":"2024-12-18 14:16:35","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":102655525,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe growth curve (A), specific growth rate (B), chlorophyll b concentration (C), and chlorophyll a concentration (D) of \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eD. salina\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003eunder blue light (BL), red light (RL), green light (GL) and white light (WL). The data represent the mean values ± SD from three biological replicates. Different letters among treatment groups (i.e., a, b, c) indicate significant differences at P \u0026lt; 0.05.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"fig.1.png","url":"https://assets-eu.researchsquare.com/files/rs-5450150/v1/1f17050105969b765d3b3114.png"},{"id":71783068,"identity":"7e3628a1-bbfb-4475-a7fd-43a7e2752b96","added_by":"auto","created_at":"2024-12-18 14:16:36","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":132217364,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe radar chart illustrates chlorophyll a fluorescence transient parameters of \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eD. salina\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e after 15 days of cultivation under different light qualities. The data represent the mean values ± SD from nine biological replicates. The chlorophyll a fluorescence transient parameters for each light quality were normalized and expressed relative to the values obtained from \"WL chlorophyll a fluorescence transient parameters\".\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"fig.2.png","url":"https://assets-eu.researchsquare.com/files/rs-5450150/v1/f8b67b26b087ecd1975403f5.png"},{"id":71783065,"identity":"66342514-fd5a-4d32-86c0-c362adccf395","added_by":"auto","created_at":"2024-12-18 14:16:36","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":137600807,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eRatio of antenna pigments to reaction center pigments (A), content of β-carotene and its cis isomers in algal suspension (B), and contents of β-carotene and its cis isomers in algal cells (C) for \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eD. salina\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e under blue light (BL), red light (RL), green light (GL), and white light (WL). The data represent the mean values ± SD from three biological replicates. Different letters among treatment groups (i.e., a, b, c, d) indicate significant differences at P \u0026lt; 0.05.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"fig.3.png","url":"https://assets-eu.researchsquare.com/files/rs-5450150/v1/c1ca8d53c962bc4cc7e7f767.png"},{"id":71783057,"identity":"c33c6ccc-0d3a-4a11-b2c8-a239dd0de5c9","added_by":"auto","created_at":"2024-12-18 14:16:34","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":362399,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eGene expression of \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eD. Salina\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e under blue light (BL), red light (RL), and white light (WL): Venn diagram illustrating the differentially expressed genes (DEGs) in \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eD. Salina \u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003eunder BL, RL, and WL (A); bar chart reflecting the regulation of differentially expressed genes (DEGs) in\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003e D. Salina \u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003ecells under BL, RL, and WL (B).\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"fig.4.png","url":"https://assets-eu.researchsquare.com/files/rs-5450150/v1/af467138f1ad1ce8f5e70838.png"},{"id":71783059,"identity":"d688d4e6-c3ee-4f55-91d6-94356255dee0","added_by":"auto","created_at":"2024-12-18 14:16:34","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":612200,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDifferentially expressed genes (DEGs) enriched in KEGG pathways of\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003e D. Salina\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e under blue light (BL), red light (RL), and white light (WL) (The number of DEGs is represented by the size of circle).\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"fig.5.png","url":"https://assets-eu.researchsquare.com/files/rs-5450150/v1/ac672e57f308f2ca12d2c2f3.png"},{"id":71784134,"identity":"1af12597-91f1-468c-9e86-3cfbceca1fc1","added_by":"auto","created_at":"2024-12-18 14:24:34","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":195009,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEffects of light qualities on the expression levels of the genes encoding phytoene synthase (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003ePSY\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e), phytoene desaturase (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003ePDS\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e), ζ-carotene desaturase (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eZDS\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e), and lycopene β-cyclase (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eLCYB\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e). The data represent the mean values ± SD from nine biological replicates. Different letters among treatment groups (i.e., a, b) indicate significant differences at P \u0026lt; 0.05. G3P: 3-phosphoglycerate, Pyr: pyruvate, \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eDXS\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e: 1-deoxy-D-xylulose-5-phosphate synthase, DXP: 1-deoxy-D-xylulose-5-phosphate, \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eDXR\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e: 1-deoxy-D-xylulose-5-phosphate reductoisomerase, MEP: 2-C-methyl-D-erythritol-4-phosphate, \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eMCT\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e: 2-C-methyl-D-erythritol-4-phosphate cytidylyltransferase, \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eMCK\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e: 2-C-methyl-D-erythritol-2,4-cyclic phosphate kinase, \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eMCS\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e: 2-C-methyl-D-erythritol-2,4-cyclic phosphatesynthase, \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eHDS\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e: (E)-1-hydroxy-(E)-2-methylbutenyl 4-diphosphate synthase, \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eIDS\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e: IPP/DMAPP synthase, IPP: isopentenyl diphosphate, DMAPP: dimethylallyl diphosphate, \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eGGPS\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e: geranylgeranyl diphosphate synthase, GGPP: geranylgeranyl diphosphate, \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003ePSY\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e: phytoene synthase, Phytoene: phytoene, \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003ePDS\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e: phytoene desaturase, ζ-carotene : ζ-carotene, \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eZDS\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e : ζ-carotene desaturase, \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eZ -ISO\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e, \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eCRTISO\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e: cis-trans isomerases, Lycopene : lycopene, \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eLCYE\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e : lycopene ε-cyclases, \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eLCYB\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e : lycopene β-cyclases, α-Carotene : α-carotenoid, β-Carotene : β-carotenoid.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"fig.6.png","url":"https://assets-eu.researchsquare.com/files/rs-5450150/v1/243e936274608a44e8f6af9a.png"},{"id":71784133,"identity":"e11bc803-e0fb-4656-9278-9a6364a6525d","added_by":"auto","created_at":"2024-12-18 14:24:34","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":159900,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEffects of monochromatic red and blue lights on the expression of the genes related to β-carotene metabolism in \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eDunaliella salina\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e. A graphical representation of the relative changes in the differentially expressed genes (DEGs) associated with the bioconversion pathways of β-carotene under red and blue lights. \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eDWARF27\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e: β-carotene isomerase, \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eLUT5\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e: β-hydroxylase, \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eZEP\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e: Zeaxanthin epoxidase, \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eNCED\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e: 9-\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003ecis \u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003eepoxycarotenoid dioxygenase, Xanthoxin: Xanthoxin aldehyde, \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eABA2\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e: Abscisic acid dehydrogenase, \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eAAO3\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e: Abscisic aldehyde oxidase.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"fig.7.png","url":"https://assets-eu.researchsquare.com/files/rs-5450150/v1/44d6fe265f99690099e254a2.png"},{"id":71783060,"identity":"5aad6ff8-6d89-4b16-9e3d-a4de080fcb57","added_by":"auto","created_at":"2024-12-18 14:16:34","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":314678,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eBalance of light absorption and photosynthetic efficiency of \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eDunaliella salina\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e under white, green, blue and red lights. Larger yellow arrows indicate stronger light. Energy\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"fig.8.png","url":"https://assets-eu.researchsquare.com/files/rs-5450150/v1/90816f473e123d2ccc6ef35a.png"},{"id":71783062,"identity":"029a06cf-311c-4113-80cc-71f73321ebb5","added_by":"auto","created_at":"2024-12-18 14:16:34","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1752227,"visible":true,"origin":"","legend":"","description":"","filename":"SupportingInformation.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5450150/v1/f4e2abd850ee2228d20d0cd9.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effects of monochromatic LED light qualities on the photosynthetic capacity and pigment content of Dunaliella salina","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003e \u003cem\u003eDunaliella salina\u003c/em\u003e is a salt-tolerant single-cell eukaryotic green alga that could accumulate large amounts of β-carotene under stress conditions such as strong light (Guermazi et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Xi et al., \u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), high temperature (G\u0026oacute;mez and Gonz\u0026aacute;lez, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2005\u003c/span\u003e), high salt (Guermazi et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), and nitrogen deficiency (Kevin and Widjaja, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). It is currently considered a promising source for the industrial production of natural β-carotene. Carotenoids are primarily stored in the cytoplasmic lipid droplets of \u003cem\u003eD. salina\u003c/em\u003e (Kim et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), accounting for up to 10% of the dry weight of \u003cem\u003eD. salina\u003c/em\u003e cells (Murthy et al., \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Lam and Lee, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Lamers et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). Today, the large-scale cultivation of \u003cem\u003eD. salina\u003c/em\u003e primarily occur in outdoor open ponds, mostly in Australia, Israel, and China (Del-Campo et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Borowitzka, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Li et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2020b\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eβ-carotene can scavenge potentially harmful free radicals and protect the immune system (G\u0026ouml;tz et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). It is commonly used as a dietary supplement for both humans and animals (Pulz and Gross, \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e2004\u003c/span\u003e), as well as a raw material for biologics (Huang et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Mizobuch \u003cem\u003eet al\u003c/em\u003e., 2023). Additionally, it plays an active role in preventing and alleviating Alzheimer's disease, Parkinson's disease, vitamin A deficiency (VAD), gastrointestinal cancer, pancreatic cancer, breast cancer, and other diseases (Fiedor and Burda, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Grune et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Leo and Lieber, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). β-carotene primarily exists in the form of isomers such as all-\u003cem\u003etrans\u003c/em\u003e, 9-\u003cem\u003ecis\u003c/em\u003e, 13-\u003cem\u003ecis\u003c/em\u003e, and 15-\u003cem\u003ecis\u003c/em\u003e (Wang et al., \u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e1994\u003c/span\u003e). Currently, all-\u003cem\u003etrans\u003c/em\u003e β-carotene is obtained mainly using chemical and biotechnological methods (Papaioannou and Liakopoulou-Kyriakides, \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Harvey and Ben-Amotz, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The β-carotene cis isomers are believed to be more bioactive than all-\u003cem\u003etrans\u003c/em\u003e β-carotene (Harvey and Ben-Amotz, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Previous studies have demonstrated that the β-carotene cis isomers may serve as an effective treatment for a range of malnutrition-related conditions like type II diabetes, chronic plaque psoriasis, and atherosclerosis (Greenberger et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Harari et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Relevy et al., \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Also, the β-carotene cis isomers can expand the antioxidant capacity of algal cells and more effectively protect reaction centers (RCs) from damage by reactive oxygen species (ROS) (Honda, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). As a result, these isomers are attracting increasing attention from researchers.\u003c/p\u003e \u003cp\u003eA high density of \u003cem\u003eD. salina\u003c/em\u003e cells is crucial and essential for the natural production of β-carotene (Fu et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). The traditional industrial model of using outdoor open ponds to cultivate \u003cem\u003eD. salina\u003c/em\u003e and accumulate natural β-carotene is gradually becoming inadequate to meet the growing demand for the substance. Open ponds do not allow light and temperature to be manipulated, making it difficult to bring the cell density of \u003cem\u003eD. salina\u003c/em\u003e cells up to 1 \u0026times; 10\u003csup\u003e6\u003c/sup\u003e cells mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Ben-Amotz, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1995\u003c/span\u003e). In order to increase the cell density of \u003cem\u003eD. salina\u003c/em\u003e and achieve a higher natural β-carotene yield, Hejazi et al. (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2004\u003c/span\u003e) modified to the cultivation process and target product extraction process of \u003cem\u003eD. salina\u003c/em\u003e. That was achieved through a change from open cultivation to closed photobioreactors, which facilitated easier artificial regulation of the expanded cultivation of \u003cem\u003eD. salin\u003c/em\u003ea. Prieto et al. (\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) analyzed the effects of cultivation methods (batch and semi-continuous) and types of photobioreactors (open and closed) on carotenoid productivity in \u003cem\u003eD. salina\u003c/em\u003e, finding that the highest carotenoid yield was achieved in a closed tubular photobioreactor. D\u0026iacute;az et al. (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) optimized their previously-designed closed tubular photobioreactor, based on the Fibonacci type, and assessed its performance in producing green \u003cem\u003eD. salina\u003c/em\u003e under environmental conditions in the Atacama Desert. The study achieved the maximum biomass productivity of \u003cem\u003eD. salina\u003c/em\u003e under strong light. Currently, utilization of photobioreactors for the cultivation of \u003cem\u003eD. salina\u003c/em\u003e cells to produce β-carotene has emerged as a focal point in research on microalgae cultivation. Compared to outdoor open ponds, photobioreactors have advantages like controllable cultivation conditions, short light paths, use of artificial light sources to supplement light energy, high mixing efficiency, and convenient CO\u003csub\u003e2\u003c/sub\u003e supply (Ma et al., \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Chen et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Tredici, \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). Thus, photobioreactors feature higher photosynthetic efficiency and production capacity (Prieto et al., \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Nowadays, the two-stage cultivation method is primarily utilized for cultivating \u003cem\u003eD. salina\u003c/em\u003e cells to produce β-carotene (Ben Amotz, 1995; Borowitzka and Borowitzka, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e1989\u003c/span\u003e; Borowitzka, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). In the initial stage known as the green cell stage, \u003cem\u003eD. salina\u003c/em\u003e cells are cultivated in an environment that enables rapid growth and biomass accumulation. Subsequently, \u003cem\u003eD. salina\u003c/em\u003e cells are transferred to and cultivated under stress conditions such as high light, high temperature, and nitrogen deficiency to enhance carotenoid production and yield. This stage is referred to as the yellow cell stage. Closed photobioreactors can have a positive impact on carotenoid production during both the green cell stage and β-carotene accumulation stage (Prieto et al., \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn large-scale cultivation using photobioreactors, the management of artificial light sources is a key technical issue that needs to be addressed first (Rozenberg et al., \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Rodr\u0026iacute;guez-Bola\u0026ntilde;os et al., \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Light intensity and wavelength are critical factors that influence the selection of artificial light sources. Light emitting diodes (LEDs) have attracted attention in microalgae cultivation and are considered suitable light sources as they make it easy to control spectral quality and have high energy efficiency (Lima et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Li and Liu, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). LEDs with different spectra, such as red, blue, white, and green, have become widely utilized in microalgae cultivation (Molina-Miras et al., \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Zhao et al., \u003cspan citationid=\"CR83\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Chen et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). In recent years, researchers have conducted \u003cem\u003eD. salina\u003c/em\u003e cultivation experiments by altering the wavelength of light source. These experiments aimed to investigate the effects of wavelengths on the growth, photosynthetic activity, and β-carotene accumulation of \u003cem\u003eD. salina\u003c/em\u003e cells. Lan et al. (\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) utilized red light to enhance the expression of \u003cem\u003eLCYB\u003c/em\u003e gene in green \u003cem\u003eD. salina\u003c/em\u003e cells, leading to an increase in β-carotene content. Similarly, Mirzaie et al. (\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) developed a red-blue flash light conversion system based on the growth curve of \u003cem\u003eD. salina\u003c/em\u003e cells to promote β-carotene synthesis. Sui et al. (\u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) conducted a comparison of β-carotene production between two types of \u003cem\u003eD. salina\u003c/em\u003e under different wavelengths of light (red, blue, and white). Their findings revealed that red light can increase the weight percentage of 9-\u003cem\u003ecis\u003c/em\u003e/all \u003cem\u003etrans\u003c/em\u003e β-carotene in \u003cem\u003eD. salina\u003c/em\u003e cells. In a separate study, Mohebi-Najafabadi and Naeimpoor (2023) investigated the effects of red light and blue light (monochromatic, or mixed) on the content of β-carotene in \u003cem\u003eD. salina\u003c/em\u003e cells during two stages of cultivation. However, to date, there have been limited studies focusing on the effects of light quality on the levels of β-carotene \u003cem\u003ecis\u003c/em\u003e isomers and the expression of key genes in β-carotene metabolic pathway within \u003cem\u003eD. salina\u003c/em\u003e cells. It remains unclear whether the β-carotene degradation process in cells is affected by light quality.\u003c/p\u003e \u003cp\u003eIn this study, we investigated the effects of monochromatic LED light quality on the photosynthetic activity and β-carotene metabolism of \u003cem\u003eD. salina\u003c/em\u003e during the green cell stage through Chl a fluorescence transient measurement and transcriptome sequencing. We also sought to determine the expression levels of key enzyme genes involved in the synthesis and degradation of β-carotene in \u003cem\u003eD. salina\u003c/em\u003e cells under different light conditions. This will help reveal the mechanism by which light quality regulates β-carotene accumulation in \u003cem\u003eD. salina\u003c/em\u003e. The findings from this study will provide a scientific basis for the technology of large-scale \u003cem\u003eD. salina\u003c/em\u003e cultivation and efficient accumulation of β-carotene in closed photobioreactors.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cp\u003e\u003cstrong\u003e2.1 Culture and treatment of plant materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe \u003cem\u003eDunaliella salina\u003c/em\u003e strain (IOCAS 879ss) was obtained from the Institute of Oceanology, Chinese Academy of Sciences, and batch-cultured in the modified Johnson medium (Borowitzka, 1988). Algae were pre-cultured under the following conditions: temperature 30 \u0026plusmn; 1℃, light intensity 80 \u0026plusmn; 10 \u0026mu;mol photons m\u003csup\u003e-2\u003c/sup\u003e s\u003csup\u003e-1\u003c/sup\u003e provided by white light-emitting diodes (LEDs) under a 12-hr light/12-hr dark cycle. During the growth phase, the cultures were manually shaken three times per day to avoid sticking.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.2 Light treatments during batch cultivation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo explore the effects of various light qualities, a batch culture was established in a precision multi-light quality combination-tuned light incubator (Taizhou Haijiang Bioengineering Technology Co., Ltd., China), with a controlled cultivation temperature of 30 \u0026plusmn; 1 ℃ and a light-dark cycle of 12h:12h. The illumination was provided by four artificial light sources of different spectral regions, i.e., blue LED strips (for blue light, BL), red LED strips (for red light, RL), white LED strips (for white light, WL), and green LED strips (for green light, GL), respectively. To guarantee the purity of the light qualities, experiments under different light resources were carefully separated using lightproof steel plates. A Spectral Scintillation Illuminometer (OHSP-350SF, Hangzhou Hongpu Light Color Technology Co., Ltd., China) was used to measure the spectra of the artificial light sources within the light incubator at a resolution of 1 nm between 350 and 700 nm (Supporting Information: Figure S1). An equation for the relationship between the incident light intensity (I\u003csub\u003ein\u003c/sub\u003e) and the average light intensity (I\u003csub\u003eav\u003c/sub\u003e) received by algal cells was set up using the simplified Lambert Beer law (Chen\u003cem\u003e\u0026nbsp;et al\u003c/em\u003e., 2011).\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003c/p\u003e\n\u003cp\u003ewhere I\u003csub\u003ein\u0026nbsp;\u003c/sub\u003erepresents the incident light intensity, I\u003csub\u003eav\u0026nbsp;\u003c/sub\u003erepresents the average light intensity received by algal cells, and T represents the transmittance (%), i.e., the ratio of the emitted light intensity to the incident light intensity.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eD. salina\u003c/em\u003e cells in the green cell stage were cultured in the light incubator. The average intensity of artificial light received by \u003cem\u003eD. salina\u003c/em\u003e cells in each of the light quality zones was kept at 40 \u0026plusmn; 5 \u0026mu;mol photons m\u003csup\u003e-2\u003c/sup\u003e s\u003csup\u003e-1\u003c/sup\u003e. Research has indicated that intense light at 800~1200 \u0026mu;mol photons m\u003csup\u003e-2\u003c/sup\u003e s\u003csup\u003e-1\u0026nbsp;\u003c/sup\u003ecan result in significant light damage to \u003cem\u003eD. salina\u003c/em\u003e, leading to impaired or even interrupted photosynthetic electron transfer in algal cells (Qin \u003cem\u003eet al\u003c/em\u003e., 2021). This makes it difficult to analyze differences in light energy allocation and utilization in \u003cem\u003eD. salina\u003c/em\u003e under different light qualities. Therefore, we chose weak light (40 \u0026plusmn; 5 \u0026mu;mol photons m\u003csup\u003e-2\u003c/sup\u003e s\u003csup\u003e-1\u003c/sup\u003e) for our experiments based on the studies that suggest neither serious photo inhibition nor significant impairment to photosynthetic electron transfer occur in \u003cem\u003eD. salina\u003c/em\u003e cells under a light intensity of 50 \u0026mu;mol photons m\u003csup\u003e-2\u003c/sup\u003e s\u003csup\u003e-1\u003c/sup\u003e (Sui\u003cem\u003e\u0026nbsp;et al\u003c/em\u003e., 2019; Capa-Robles \u003cem\u003eet al\u003c/em\u003e., 2021; Kim \u003cem\u003eet al\u003c/em\u003e., 2024). The use of weak light below 50 \u0026mu;mol photons m\u003csup\u003e-2\u003c/sup\u003e s\u003csup\u003e-1\u003c/sup\u003e helps analyze differences in \u0026beta;-carotene metabolism under various light qualities in \u003cem\u003eD. salina\u003c/em\u003e cells.\u003c/p\u003e\n\u003cp\u003eThree biological replicates were set up under each light quality. Green algal cells were cultured for 15 days, with the culture collected every 3 days to determine algal cell density and photosynthetic pigment content. On the 15th day, all green algal cells were harvested to measure cellular light absorption, Chl a fluorescence transient, and intracellular contents of \u0026beta;-carotene and its cis isomers. Also, quantitative Polymerase Chain Reaction (qPCR) analysis and transcriptomic analysis were carried out.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.3 Measurement of cell density and specific growth rate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe cell density was manually counted using a hemocytometer and an inverted microscope (Shanghai Optical Instrument Factory, Co., Ltd., China) with 37 XB magnification. The specific growth rate (\u0026mu;) of \u003cem\u003eD. salina\u003c/em\u003e cells was calculated using the following formula (Moheimani and Parlevliet, 2013):\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003c/p\u003e\n\u003cp\u003ewhere N\u003csub\u003e2\u003c/sub\u003e (final) and N\u003csub\u003e1\u003c/sub\u003e (initial) are the cell densities (cells mL\u003csup\u003e-1\u003c/sup\u003e) determined using a hemocytometer at the times T\u003csub\u003e2\u003c/sub\u003e and T\u003csub\u003e1\u003c/sub\u003e, respectively.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.4 Measurement of pigment content\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe improved ethanol extraction method (Danesh \u003cem\u003eet al\u003c/em\u003e., 2017) and spectrophotometric method proposed by Arnon (1949) were used to measure the contents of chlorophyll a (Chl a) and chlorophyll b (Chl b) in the culture. Briefly, 5 mL of culture media was centrifuged at 10,000 g for 10 min using a centrifuge (TGL-16 M, Changzhou Jintan Liangyou Instrument Co. Ltd., China). After the supernatant was removed, the cell pellet was dissolved in 5 mL of 95% ethanol and extracted under darkness for 24 h. Then, the extract was centrifuged at 10,000 g for 10 min at 4℃. The resulted supernatant was used for the quantization of pigments as follows:\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003c/p\u003e\n\u003cp\u003ewhere A represents the absorbance at the indicated wavelength.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.5 Measurement of light absorption and Chl a fluorescence transient\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe average extinction coefficients at different wavebands, i.e., BL (400\u0026ndash;480 nm), GL (500\u0026ndash;560 nm), RL (600\u0026ndash;650 nm), and photosynthetic active radiation (PAR, 400\u0026ndash;700 nm), were determined as described by Li and Meng (2014). Microalgae precultured in LED white light as described in the \u0026ldquo;Culture and treatment of plant materials\u0026rdquo; section were used to determine the light absorption to avoid the possible influence of light acclimation on light absorption. The transmittances were recorded by scanning the supernatant. The average light transmittance (\u003cem\u003eT\u003c/em\u003e) and mean extinction coefficient (\u003cem\u003ea\u003c/em\u003e) of the algal suspension were calculated with the equation below.\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003c/p\u003e\n\u003cp\u003ewhere \u0026lambda;d and \u0026lambda;u are the lower-limit wavelength and upper-limit wavelength of each light quality, respectively; T(\u0026lambda;) represents the monochromatic light transmittance of each wavelength (%); S(\u0026lambda;) is the relative spectral power distribution on the corresponding wavelength (W); V(\u0026lambda;) stands for the efficiency of spectral illumination of the corresponding wavelength. The values of S(\u0026lambda;) and V(\u0026lambda;) can be obtained from the information given by the International Commission on Illumination (CIE) and the National Standardization Technical Committee (2008). According to CIE, the sampling interval established to obtain values of S(\u0026lambda;) and V(\u0026lambda;) is 5 nm in the range 400\u0026ndash;700 nm. The specific extinction coefficient of mixed light quality was expressed as the average value of each monochrome light quality. Ae refers to the proportion of the incident light absorbed by algal suspension or pigment extract.\u003c/p\u003e\n\u003cp\u003eThe cuvettes containing the algal suspension under different light qualities were initially dark adapted for 20 min. Then, the Chl a fluorescence transient was measured using the FluorPen software (AquaPen Ap110-C, Czech Republic) according to Li \u003cem\u003eet al\u003c/em\u003e. (2024). Saturated red light at 3000 \u0026mu;mol photons m\u003csup\u003e-2\u0026nbsp;\u003c/sup\u003es\u003csup\u003e-1\u0026nbsp;\u003c/sup\u003ewas produced by an array of light-emitting diodes (LED, peak 650 nm). The Chl a fluorescence transient was obtained using 2 s of saturated red light, and analyzed with the OJIP transient in line with the OJIP-test procedure proposed by Strasser and Strasser (1995). The relevant Chl a fluorescence transient parameters and their biological significances revealed by the JIP test are shown in Table 1.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1 Chl a fluorescence transient parameters (\u003c/strong\u003e\u003cstrong\u003eStrasser\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;\u003cem\u003eet al\u003c/em\u003e. 2004\u003c/strong\u003e\u003cstrong\u003e)\u003c/strong\u003e\u003c/p\u003e\n\u003cdiv align=\"Left\"\u003e\n \u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"588\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 294px;\"\u003e\n \u003cp\u003eParameters\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 294px;\"\u003e\n \u003cp\u003eBiological significance\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 294px;\"\u003e\n \u003cp\u003eFv/Fm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 294px;\"\u003e\n \u003cp\u003eMaximum photochemical efficiency of the PSII\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 294px;\"\u003e\n \u003cp\u003ePI\u003csub\u003eABS\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 294px;\"\u003e\n \u003cp\u003ePerformance index on absorption basis\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 294px;\"\u003e\n \u003cp\u003eABS/RC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 294px;\"\u003e\n \u003cp\u003eAbsorption flux per RC\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 294px;\"\u003e\n \u003cp\u003eTR\u003csub\u003e0\u003c/sub\u003e/RC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 294px;\"\u003e\n \u003cp\u003eTrapped energy flux per RC (at t=0)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 294px;\"\u003e\n \u003cp\u003eET\u003csub\u003e0\u003c/sub\u003e/RC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 294px;\"\u003e\n \u003cp\u003eElectron transport flux per RC (at t=0)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 294px;\"\u003e\n \u003cp\u003eDI\u003csub\u003e0\u003c/sub\u003e/RC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 294px;\"\u003e\n \u003cp\u003eDissipated energy flux per RC (at t=0)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 294px;\"\u003e\n \u003cp\u003e1-Vj\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 294px;\"\u003e\n \u003cp\u003eProbability (at t = 0) that a trapped exciton moves an electron into the electron transportchain beyond Q\u003csub\u003eA\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cstrong\u003e2.6 Measurement of algal cell size\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e2 mL of the agal culture was centrifuged at 10,000 g for 10 s using a centrifuge (TGL-16 M, Changzhou Jintan Liangyou Instrument Co. Ltd., China) to concentrate the algal cells. The algal cells were observed and imaged under an inverted microscope (Shanghai Optical Instrument Factory, Co., Ltd., China) at 37 XB. The open-source platform Image J (Rasband, 2012) was used for image analysis and the measurement of algal cell area (\u0026mu;m\u003csup\u003e2\u003c/sup\u003e) and diameter (\u0026mu;m). Forty cells were randomly selected per light quality to determine their areas and diameters.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.7 Measurement of \u0026beta;-Carotene and its geometric isomers\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe contents of \u0026beta;-carotene and its geometric isomers were determined through high performance liquid chromatography (HPLC) (Priscilla \u003cem\u003eet al\u003c/em\u003e., 2024; Mazzucchi \u003cem\u003eet al\u003c/em\u003e., 2020). The specific chromatographic conditions were as follows: high-performance liquid chromatograph: Agilent 1260 Infinity II; chromatographic column: C30 YMC\u003csup\u003eTM\u0026nbsp;\u003c/sup\u003eCarotenoid (4.6 mm\u0026times;250 mm, 5 \u0026mu;m); mobile phase A: acetonitrile-methanol (3:1, V/V), with the addition of 0.05% triethylamine (V/V), treated through ultrasonic degassing before use; mobile phase B: MTBE (methyl tert-butyl ether), with the addition of 0.05% triethylamine (V/V), treated through ultrasonic degassing before use; gradient: within 8 min, the content of mobile phase B increased linearly from 0% to 55%, and then maintained at 55% for another 27 min; flow rate: 1.0 mL/min; detection wavelength: 475 nm; injection volume: 20 \u0026mu;L; column temperature: 30 ℃.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.8 Quantitative Polymerase Chain Reaction\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe RNA of the algal cells cultured under different light conditions for 15 days was extracted using the Total RNA Extraction Kit (AikeRui Biotech, China). The first-strand cDNA was synthesized using the First-Strand cDNA Synthesis Kit (Tiangen, Beijing, China), and the full-length coding sequence of the gene was cloned from the cDNA. Real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis was performed according to the MIQE guidelines (Bustin \u003cem\u003eet al\u003c/em\u003e., 2010) using a fully automated fluorescence quantitative PCR system. The qRT-PCR thermal cycling conditions were as follows: pre-denaturation at 95\u0026deg;C for 30 s, followed by 40 cycles of denaturation at 95\u0026deg;C for 5 s, annealing at 60\u0026deg;C for 15 s, and extension at 72\u0026deg;C for 20 s. Primers were designed according to Li \u003cem\u003eet al\u003c/em\u003e. (2020a), with \u0026beta;-Tubulin used as an internal reference gene. The primer sequences are listed in Supporting Information: Table S1. Three biological replicates were performed for each gene, and statistical analysis was conducted using the standard curve method.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.9 Transcriptomic analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eRNA sequencing and standard bioinformatic analyses were carried out by Biomarker Technologies Co., Ltd. (Wang \u003cem\u003eet al\u003c/em\u003e., 2009). In brief, total RNA was extracted from DN and DH treatment samples, and first‐strand cDNA was synthesized using random hexamer primer and M‐MuLV Reverse Transcriptase. To select cDNA fragments of preferentially 240 bp in length, the library fragments were purified with the AMPure XP system (Beckman Coulter). Then, 3 \u0026mu;L of USER Enzyme (NEB) was used with size‐selected, adaptor‐ligated cDNA at 37\u0026deg;C for 15min followed by 5min at 95\u0026deg;C before PCR. Thereafter, PCR was performed with Phusion High‐Fidelity DNA polymerase, Universal PCR primers, and Index (X) Primer. Finally, PCR products were purified (AMPure XP system) and library quality was assessed on the Agilent Bioanalyzer 2100 system. On that basis, the libraries were sequenced using an Illumina Hiseq X‐ten platform, PE 240 bp. The sequences were further processed with a bioinformatic pipeline tool, BMKCloud (www.biocloud.net) online platform. Gene functions were annotated based on the following databases: NR (NCBI nonredundant protein sequences), Pfam (Protein family), KOG/COG/eggNOG (Clusters of Orthologous Groups of proteins), Swiss‐Prot (A manually annotated and reviewed protein sequence database), KEGG (Kyoto Encyclopedia of Genes and Genomes), and GO (Gene Ontology) (|log\u003csub\u003e2\u003c/sub\u003eFC | \u0026gt; 1, false discovery rate (FDR) \u0026lt; 0.05). Each sample had three replicates and the annotation was repeated three times. GO pathway enrichment analysis and KEGG pathway enrichment analysis were performed through the topGO R packages‐based Kolmogorov\u0026ndash;Smirnov test and KOBAS software, respectively. The raw sequence reads have been deposited in the NCBI database under the accession number PRJNA856777.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.10 Statistical analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData in the figures, representing the averages of replicates \u0026plusmn; standard deviation (SD), were subject to one-way ANOVA complemented by a least significant difference post hoc test, which was conducted using the software SPSS Statistics 26.0. All the data were tested for normality and homogeneity of variance to check whether they meet statistical requirements. When a significant difference was found, a post-hoc comparison-of-means test (Tukey or Games-Howell test) would be carried out to determine which values differed significantly. A \u003cem\u003ep\u003c/em\u003e-value below 0.05 was considered statistically significant.\u003c/p\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Effects of light quality on algal cell growth and pigment content\u003c/h2\u003e \u003cp\u003eDuring the 15-day cultivation period, the algae showed logarithmic growth under all four light qualities, with the highest cell density observed under BL (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA). The maximum specific growth rate \u0026micro; (0.066\u0026thinsp;\u0026plusmn;\u0026thinsp;0.005 d\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) was also observed under BL, slightly higher than the specific growth rates under WL (0.063\u0026thinsp;\u0026plusmn;\u0026thinsp;0.007 d\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and RL (0.060\u0026thinsp;\u0026plusmn;\u0026thinsp;0.005 d\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), and significantly higher than that under GL (0.050\u0026thinsp;\u0026plusmn;\u0026thinsp;0.004 d\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB). BL considerably increased the contents of Chl a and Chl b in both algal culture and cells (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eC, D). This indicates that BL is more conducive to algal cell division, proliferation, and chlorophyll synthesis.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Light absorption of \u003cem\u003eD. salina\u003c/em\u003e in different spectra\u003c/h2\u003e \u003cp\u003eFor \u003cem\u003eD. salina\u003c/em\u003e cells, the light absorption (Ae) at all the four wavelengths is relatively low, with no more than 40% of incident light being absorbed (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). However, there is a significant difference in the light absorption rate and pigment extracts of \u003cem\u003eD. salina\u003c/em\u003e cells at different wavelengths. The highest Ae value for \u003cem\u003eD. salina\u003c/em\u003e cells is observed in the blue wavelength (37.9%), followed by the white (31.3%), red (22.8%), and green (22.1%) wavelengths. As for pigment extracts, the highest Ae value is also in the blue wavelength (22.8%), followed by the red (18.6%), white (14.0%), and green (10.2%). This indicates that both \u003cem\u003eD. salina\u003c/em\u003e cells and pigments absorb more light energy in the blue wavelength than in the other wavelengths.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAverage transmittance (T: %) and proportion of absorbed incident light (Ae: %) of cells and pigment extracts in \u003cem\u003eDunaliella salina\u003c/em\u003e at different wavebands, namely white light (WL, 400\u0026thinsp;~\u0026thinsp;700 nm), blue light (BL, 400\u0026thinsp;~\u0026thinsp;500 nm), red light (RL, 570\u0026thinsp;~\u0026thinsp;680 nm) and green light (GL, 450\u0026thinsp;~\u0026thinsp;600 nm), respectively\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eAlgal cells\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003ePigment extracts\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eRatio of pigment absorption to cell absorption/%\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLight source\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eT/%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAe/%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eT/%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eAe/%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e62.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e37.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e77.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e22.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e60.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e77.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e22.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e89.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e46.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e68.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e31.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e86.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e14.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e44.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e77.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e22.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e81.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e18.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e81.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Effects of light quality on photosynthetic efficiency\u003c/h2\u003e \u003cp\u003eThe fluorescence intensity of the OJIP curve of \u003cem\u003eD. salina\u003c/em\u003e cultivated under BL was much higher than those under other light qualities (Supporting Information: Figure S4). Different light qualities greatly affected the photosynthetic capacity of \u003cem\u003eD. salina\u003c/em\u003e cells and the light energy absorption of PSII reaction centers (RCs). The highest values of Fv/Fm and \u003cb\u003ePI\u003c/b\u003e\u003csub\u003e\u003cb\u003eABS\u003c/b\u003e\u003c/sub\u003e were observed under BL, exceeding those under the other light qualities. On the other hand, the values of Fv/Fm and Pi_ABS under GL were lower than those under the other light qualities. This indicates that BL can increase the photosynthetic capacity of \u003cem\u003eD. salina\u003c/em\u003e and improve the photosynthetic efficiency of RC, whereas GL is not conducive to expanding the photosynthetic capacity. Similarly, the ABS/RC, TR\u003csub\u003e0\u003c/sub\u003e/RC, ET\u003csub\u003e0\u003c/sub\u003e/RC, and 1-V\u003csub\u003eJ\u003c/sub\u003e values under BL were all higher than those under the other light qualities, while the values under GL were at relatively lower levels. However, in terms of the DI\u003csub\u003e0\u003c/sub\u003e/RC value under GL was higher than those under the other light qualities. This suggests that BL increased PSII RCs\u0026rsquo; capability to absorb, capture and transfer light energy while reducing energy dissipation. Attributed to that, PSII RCs are more efficient in utilizing light energy under BL than under the other light qualities. On the contrary, under GL, PSII RCs reduced their capability to absorb, capture and transfer light energy while increasing energy dissipation. That resulted in a lower utilization efficiency of light energy (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Effects of light quality on contents of β-carotene isomers\u003c/h2\u003e \u003cp\u003eSignificant differences in the pigment ratio of \u003cem\u003eD. salina\u003c/em\u003e under different light qualities were observed (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05) during the 15-day cultivation period. Under BL, the ratio of antenna pigments (Chl b\u0026thinsp;+\u0026thinsp;Car) to reaction center pigments (Chl a) reached a maximum of 0.87, followed by 0.83 under RL and 0.78 under WL. The lowest pigment ratio, 0.72, occurred under GL (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA). This indicates that BL is more favorable for the absorption and transfer of solar energy in \u003cem\u003eD. salina\u003c/em\u003e cells compared to the other light qualities.\u003c/p\u003e \u003cp\u003eThrough HPLC analysis, three geometric isomers of β-carotene were identified: all-\u003cem\u003etrans\u003c/em\u003e β-carotene, 9-\u003cem\u003ecis\u003c/em\u003e β-carotene, and 13-\u003cem\u003ecis\u003c/em\u003e β-carotene. Significant differences were noted in the contents of β-carotene and its cis isomers within both algal suspension and cells under BL, RL, and WL (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The highest concentration of all-\u003cem\u003etrans\u003c/em\u003e β-carotene in algal suspension, 11.46 mg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, occurred under BL, much higher than the concentrations recorded under RL (9.41 mg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and WL (2.46 mg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). However, RL resulted in substantially higher levels of both 9-cis β-carotene (5.09 mg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and 13-cis β-carotene (2.62 mg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), surpassing those found under BL and WL (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB).\u003c/p\u003e \u003cp\u003eThe variations in cellular contents of β-carotene and its cis isomers across BL, RL, and WL differed from those observed in algal liquids (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC). The content of all-\u003cem\u003etrans\u003c/em\u003e β-carotene under BL was found to be the highest, measuring 1.48 pg cell\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The cellular content of 9-\u003cem\u003ecis\u003c/em\u003e β-carotene showed no significant differences between RL and WL, but was much higher under these two light qualities than under BL (0.23 pg cell\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). Similarly, the accumulation pattern of 13-\u003cem\u003ecis\u003c/em\u003e β-carotene in response to different light qualities was consistent with that of 9-\u003cem\u003ecis\u003c/em\u003e β-carotene. The 13-\u003cem\u003ecis\u003c/em\u003e β-carotene concentrations observed under RL and WL were 0.23 pg cell\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 0.21 pg cell\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e respectively, both greatly exceeding that observed under BL (0.13 pg cell\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). These results indicate that BL is conducive to the accumulation of all-\u003cem\u003etrans\u003c/em\u003e β-carotene in \u003cem\u003eD. salina\u003c/em\u003e cells, whereas RL promotes the accumulation of both 9-\u003cem\u003ecis\u003c/em\u003e and 13-\u003cem\u003ecis\u003c/em\u003e β-carotenes in these cells.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Effects of light quality on gene expression in \u003cem\u003eD. Salina\u003c/em\u003e\u003c/h2\u003e \u003cp\u003eUnder GL, the growth of \u003cem\u003eD. Salina\u003c/em\u003e cells is slow, and the light absorption and photosynthetic activity are weak. This indicates that GL cannot promote the growth of \u003cem\u003eD. Salina\u003c/em\u003e cells in the green stage. Given that, only \u003cem\u003eD. Salina\u003c/em\u003e cells cultivated under BL, RL, and WL were selected for non-reference transcriptomic analysis. In this study, a total of 9,187 differentially expressed genes (DEGs) were identified. The Venn diagram of transcriptomics shows that totally there are 7,968 genes exhibiting differential expression between the BL and RL treatment groups, between the BL and WL treatment groups, as well as between the RL and WL treatment groups. Notably, DEGs primarily occur between the BL and WL treatment groups, and between the RL and WL treatment groups. This suggests that the effects of RL and BL on gene expression in \u003cem\u003eD. Salina\u003c/em\u003e are somewhat similar (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB reveals the differences in the number of DEGs among the treatment groups under varying light conditions, as well as their upregulation and downregulation. As shown in the bar chart, there are 8,256 DEGs between the RL and WL treatment groups, including 294 upregulated genes and 7,962 downregulated genes; between the BL and WL treatment groups, there are 8,745 DEGs, including 73 upregulated genes and 8,672 downregulated genes (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB). The KEGG pathway enrichment analysis demonstrates that the DEGs are primarily enriched in various metabolic processes, including the β-carotene biosynthesis pathway, sphingolipid metabolism pathway, steroid biosynthesis pathway, and fatty acid elongation pathway (Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA and B). These findings suggest that RL and BL predominantly influence metabolism-related genes in \u003cem\u003eD. Salina\u003c/em\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e3.6 Effects of light quality on the expression of β-Carotene metabolic enzyme genes in \u003cem\u003eD. salina\u003c/em\u003e\u003c/h2\u003e \u003cp\u003eThe enzymes phytoene synthase (\u003cem\u003ePSY\u003c/em\u003e), phytoene desaturase (\u003cem\u003ePDS\u003c/em\u003e), ζ-carotene desaturase (\u003cem\u003eZDS\u003c/em\u003e), and lycopene β-cyclase (\u003cem\u003eLCYB\u003c/em\u003e) play positive roles in the biosynthesis of β-carotene in plants (Amendola et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Chen et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Sathasivam and Ki, \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Lan et al., \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Among these, \u003cem\u003ePSY\u003c/em\u003e is identified as the rate-limiting enzyme in the β-carotene biosynthetic pathway (Liang et al., \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Li et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). There were no significant differences observed in the relative expression levels of \u003cem\u003ePSY\u003c/em\u003e, \u003cem\u003ePDS\u003c/em\u003e and \u003cem\u003eZDS\u003c/em\u003e under BL, RL, and WL. However, \u003cem\u003eLCYB\u003c/em\u003e reached the highest relative expression level under WL (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e).The enzymes β-hydroxylase (\u003cem\u003eLUT5\u003c/em\u003e), Zeaxanthin epoxidase (\u003cem\u003eABA1\u003c/em\u003e), Abscisic acid dehydrogenase (\u003cem\u003eABA2\u003c/em\u003e) play positive roles in the degradation of β-carotene in plants (Zhao et al., \u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Jia et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Tolnai et al., \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Compared to WL, the relative expression levels of \u003cem\u003eLUT5\u003c/em\u003e, \u003cem\u003eABA1\u003c/em\u003e and \u003cem\u003eABA2\u003c/em\u003e were prominently downregulated under BL; the relative expression levels of \u003cem\u003eLUT5\u003c/em\u003e and \u003cem\u003eABA2\u003c/em\u003e were markly downregulated under RL, but the expression levels of \u003cem\u003eABA1\u003c/em\u003e was upregulated under RL (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eLight quality is a crucial factor influencing the metabolism, growth, and reproduction of algal cells. Our research indicated that monochromatic light qualities can affect the light absorption characteristics and photosynthetic efficiency of \u003cem\u003eD. Salina\u003c/em\u003e, and regulate the expression of key enzyme genes involved in the \u0026beta;-carotene biosynthesis pathway in \u003cem\u003eD. Salina.\u003c/em\u003e Under BL, algal cells had the highest growth rate (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eA, B). Additionally, the bioconversion pathway from \u0026beta;-carotene to abscisic acid was significantly inhibited under BL (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e), which thus reduced the degradation of \u0026beta;-carotene and facilitated its accumulation within algal cells.\u003c/p\u003e\n\u003cp\u003ePrevious studies showed that strong light stress can lead to the accumulation of carotenoids in \u003cem\u003eD. Salina\u003c/em\u003e cells (Ye et al., \u003cspan class=\"CitationRef\"\u003e2008\u003c/span\u003e). However, our study featured an average light intensity of 40 \u0026micro;mol photons m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which is insufficient to induce photoinhibition in \u003cem\u003eD. Salina\u003c/em\u003e cells (Sui et al., \u003cspan class=\"CitationRef\"\u003e2019\u003c/span\u003e; Capa-Robles et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e; Kim et al., \u003cspan class=\"CitationRef\"\u003e2024\u003c/span\u003e). Therefore, the differences in the cell density and specific growth rate of \u003cem\u003eD. Salina\u003c/em\u003e are primarily attributed to variations in light quality. Our results indicate that the specific growth rate under BL is slightly higher than those under RL and WL, and significantly higher than that under GL (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eA, B). Thus, for microalgal cultivation, BL and RL irradiation are considered efficient, while GL irradiation is regarded as less effective (Wagner et al., \u003cspan class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eTable \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e shows that a portion of incident light is absorbed by the cells across four different light qualities (ranging from 22.1\u0026ndash;37.9%). The absorption by pigments is slightly lower than that by the cells themselves, ranging from 10.2\u0026ndash;22.8%. Supporting Information: Figure S2 and S3 indicated that there were no significant differences in cell size among the \u003cem\u003eD. Salina\u003c/em\u003e cultures under different light qualities. In light of that, the disparities observed in cellular and pigment absorption rates across various wavelengths cannot be attributed to differences in algal cell size. Rather, they reflect variations in absorption capabilities of \u003cem\u003eD. Salina\u003c/em\u003e cells and pigments with different spectral bands.\u003c/p\u003e\n\u003cp\u003eAmong the light qualities involved in our study, BL and RL provide the highest and second highest pigment-level absorption rates, respectively (22.8% and 18.6%), whereas GL has a lower pigment-level absorption rate, no more than 10.2%. The discrepancies between cellular and pigment-level absorptive capacities effectively represent variations in pigment content of \u003cem\u003eD. Salina\u003c/em\u003e under different light qualities (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). This finding aligns with our earlier observations on other species of \u003cem\u003eDunaliella sp.\u003c/em\u003e such as \u003cem\u003eDunaliella sp.\u003c/em\u003e MACC/C43 (Li et al., \u003cspan class=\"CitationRef\"\u003e2020b\u003c/span\u003e). We further hypothesize that RL offers the highest effective absorption rate, approximately 81.8%, which helps maintain a balance between algal cell photoabsorption and utilization efficiency. This allows for sustained high photosynthetic activity even at lower chlorophyll levels within cells. However, both photoabsorption by algal cells (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e) and the efficiency of energy utilization by RCs under RL do not match those achieved under BL. As a result, the cell proliferation rate and pigment content under RL are lower than those under BL.\u003c/p\u003e\n\u003cp\u003eIn cells, chloroplasts containing pigments exist within a complex molecular environment. Other cellular components, such as proteins, carbohydrates, and lipids, have distinct optical properties that can diminish the light energy reaching PSII reaction centers of algal cells (Johnsen and Sakshaug, \u003cspan class=\"CitationRef\"\u003e2007\u003c/span\u003e; Lehmuskero et al., 2017). Light quality strongly influences both pigment content and composition in \u003cem\u003eD. Salina\u003c/em\u003e cells (Figs. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eC, D; Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). In this study, the ratio of light-harvesting antenna pigments to reaction center pigments in \u003cem\u003eD. Salina\u003c/em\u003e under BL are significantly different to those under the other light qualities (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eA). This finding is consistent with previous studies (Gorai et al., \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e; Li and Liu, \u003cspan class=\"CitationRef\"\u003e2020\u003c/span\u003e). Therefore, a logical explanation is that exposure to monochromatic light may play an active role in pigment synthesis. The ratio of light-harvesting pigments (Chl-b\u0026thinsp;+\u0026thinsp;Car) to antenna pigments (Chl-a) is considered indicative of the photonic capture capability of a PSII reaction center (Ueno et al., \u003cspan class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eThe ratio of light-harvesting pigments to reaction center pigments under BL is significantly higher than those under the other light qualities (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eA), facilitating enhanced capture and absorption of light energy. This observation is corroborated by the results concerning chlorophyll fluorescence transients (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). Similarly, the elevated values of F\u003csub\u003eV\u003c/sub\u003e/Fm, Pi-ABS, ABS/RC, TR\u003csub\u003e0\u003c/sub\u003e/RC, ET\u003csub\u003e0\u003c/sub\u003e/RC, and 1-V\u003csub\u003eJ\u003c/sub\u003e under BL indicate improvements in the efficiency of the photosynthetic electron transport chain and the photosynthetic capacity of algal cells as a result of BL exposure (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). Furthermore, the increased DI\u003csub\u003e0\u003c/sub\u003e/RC value under GL suggests a rise in thermal dissipation at PSII reaction centers of \u003cem\u003eD. Salina\u003c/em\u003e and a reduction in the rate of electron transfer from Q\u003csub\u003eA\u003c/sub\u003e to Q\u003csub\u003eB\u003c/sub\u003e during GL exposure. In conclusion, we propose that light intensity being low, \u003cem\u003eD. Salina\u003c/em\u003e cells are more effective at absorbing and transferring light energy to PSII under BL than under other light qualities. Thus, carbon assimilation processes within these cells are more efficient under BL, resulting in higher photosynthetic efficiency and growth rates. Conversely, under GL, a greater portion of absorbed light energy is dissipated at PSII reaction centers to reduce both the rate of photosynthetic electron transport and overall photosynthetic efficiency. This is how the pigment content of \u003cem\u003eD. Salina\u003c/em\u003e cells lowers and their growth slows down under GL.\u003c/p\u003e\n\u003cp\u003eBased on the abovementioned proposal, we developed a model to explain how halophytic algae maintain a balance between light absorption and energy utilization under different light qualities (Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e). The results of qPCR (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e) further support our inference. Specifically, there were no significant differences in the expression levels of key enzyme genes involved in the \u0026beta;-carotene synthesis pathway\u0026mdash;such as \u003cem\u003ePSY\u003c/em\u003e, \u003cem\u003ePSD\u003c/em\u003e, \u003cem\u003eZDS\u003c/em\u003e\u0026mdash;in \u003cem\u003eD. Salina\u003c/em\u003e cells under varying light qualities (BL, WL, and RL) (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e). Song et al. (\u003cspan class=\"CitationRef\"\u003e2023\u003c/span\u003e) found that the expression of \u003cem\u003eLCYB\u003c/em\u003e is upregulated under far red light. We speculate that the expression of \u003cem\u003eLCYB\u003c/em\u003e may be regulated by the spectral range of light, and monochromatic light (i.e.,BL, RL, and GL) may downregulate the expression level of \u003cem\u003eLCYB.\u003c/em\u003e This is why the upregulation of \u003cem\u003eLCYB\u003c/em\u003e gene expression under WL is observed in \u003cem\u003eD. salina.\u003c/em\u003e Therefore, we can infer that the expression levels of these key enzyme genes exert no influence on \u0026beta;-carotene content within \u003cem\u003eD. Salina\u003c/em\u003e cells. This indicates that the differences in \u0026beta;-carotene synthesis capacity among \u003cem\u003eD. Salina\u003c/em\u003e cells under different light qualities are attributed to variations in these cells\u0026rsquo; capability to absorb and utilize light energy.\u003c/p\u003e\n\u003cp\u003eFigures \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eC and D indicate that monochromatic RL and BL, compared to WL, can increase the content and activity of \u0026beta;-carotene and its cis-isomers in algal cultures. This phenomenon has been reported in several previous studies (Sui et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e; Mohebi-Najafabadi and Naeimpoor, 2023; Mirzaie et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e). However, the mechanisms underlying the effects of light qualities on \u0026beta;-carotene accumulation in \u003cem\u003eD. Salina\u003c/em\u003e remain unclear. In this study, we performed qPCR and transcriptomic analysis to assess gene expression in \u003cem\u003eD. Salina\u003c/em\u003e under different light qualities. The influence of RL and BL on gene expression was largely similar: as illustrated by the Venn diagram, there are 7,848 genes co-affected by RL and BL (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eA). Notably, most of these affected genes were downregulated (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eB), characterized by a great concentration among metabolism-related pathways. Furthermore, four differentially expressed genes (DEGs) were identified within the \u0026beta;-carotene biosynthetic pathway (Figs. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eA and B). Our findings further demonstrate that monochromatic BL exerts a more pronounced effect on the metabolic pathway genes associated with \u0026beta;-carotene in \u003cem\u003eD. Salina\u003c/em\u003e (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eThis study employed qPCR to measure the expression levels of \u003cem\u003ePSY\u003c/em\u003e, \u003cem\u003ePDS\u003c/em\u003e, \u003cem\u003eZDS\u003c/em\u003e, and \u003cem\u003eLCYB\u003c/em\u003e in \u003cem\u003eD. Salina\u003c/em\u003e under different light qualities, as a step to investigate the influence of light qualities on the \u0026beta;-carotene synthesis pathway. The transcriptomic analysis revealed that four differentially expressed genes (DEGs) were primarily enriched in the carotenoid metabolism pathway. To elucidate the differences in gene expression related to carotenoid synthesis and degradation pathways under varying light, we built two models (Figs. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e). Figure \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e illustrates that there are no significant differences in the relative expression levels of \u003cem\u003ePSY\u003c/em\u003e, \u003cem\u003ePDS\u003c/em\u003e, and \u003cem\u003eZDS\u003c/em\u003e among BL, RL, and WL; however, under GL, their relative expression levels were significantly higher than those observed under other light qualities. We hypothesize that this increase in \u003cem\u003ePSY\u003c/em\u003e, \u003cem\u003ePDS\u003c/em\u003e, and \u003cem\u003eZDS\u003c/em\u003e expression may be associated with a negative feedback regulation mechanism employed by \u003cem\u003eD. Salina\u003c/em\u003e cells to dissipate excess light energy. Amid GL exposure where \u003cem\u003eD. Salina\u003c/em\u003e cells utilize light inefficiently, carotenoids can serve as structural and functional pigments within the photocomplexes involved in non-photochemical quenching (Dall\u0026apos;Osto et al., \u003cspan class=\"CitationRef\"\u003e2006\u003c/span\u003e). PSII reaction centers of microalgae dissipate excess light energy primarily through both photochemical quenching and non-photochemical quenching pathways (Crepin and Caffarri, \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e). In order to mitigate excess light energy during GL exposure, algae cells upregulate the expression of genes such as \u003cem\u003ePSY\u003c/em\u003e, \u003cem\u003ePDS\u003c/em\u003e, and \u003cem\u003eZDS\u003c/em\u003e to synthesize more carotenoids as a means of non-photochemical quenching. The elevated DI\u003csub\u003e0\u003c/sub\u003e/RC ratio observed under GL further supports this inference.\u003c/p\u003e\n\u003cp\u003eXu and Harvey (\u003cspan class=\"CitationRef\"\u003e2019\u003c/span\u003e) compared the ratios of all-\u003cem\u003etrans\u003c/em\u003e \u0026beta;-carotene to 9-\u003cem\u003ecis\u003c/em\u003e \u0026beta;-carotene in \u003cem\u003eDunaliella salina\u003c/em\u003e under monochromatic RL and BL. They found that RL upregulates the activity of 9-\u003cem\u003ecis\u003c/em\u003e-\u0026beta;C-ISO, an enzyme converting all-\u003cem\u003etrans\u003c/em\u003e \u0026beta;-carotene into its cis isomers. They hypothesized that under RL, \u003cem\u003eD. salina\u003c/em\u003e enhances the synthesis of 9-\u003cem\u003ecis\u003c/em\u003e \u0026beta;-carotene to rapidly expand its antioxidant pool, thus reducing the formation rate of reactive oxygen species (ROS). Similarly, we observed that under RL, \u003cem\u003eD. salina\u003c/em\u003e cells synthesized higher levels of cis isomers (including 9-\u003cem\u003ecis\u003c/em\u003e and 13-\u003cem\u003ecis\u003c/em\u003e \u0026beta;-carotene), while under BL, there was a greater accumulation of all-\u003cem\u003etrans\u003c/em\u003e \u0026beta;-carotene (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). Ben-Amotz et al. (\u003cspan class=\"CitationRef\"\u003e1989\u003c/span\u003e) reported significant photoinhibition in \u003cem\u003eD. salina\u003c/em\u003e cells exposed to high-intensity RL, which led to substantial production of ROS. The mechanism Xu and Harvey proposed for ROS clearance may be one reason why a higher proportion of cis isomeric forms occurs under RL than under BL.\u003c/p\u003e\n\u003cp\u003eInterestingly, we found that the differences in \u0026beta;-carotene content under different light qualities are associated with not only the upstream synthesis but also the downstream degradation in the \u0026beta;-carotene metabolic pathway. Abscisic acid (\u003cem\u003eABA\u003c/em\u003e) is a plant hormone derived from carotenoid precursors. Its biosynthesis begins with the conversion of all-\u003cem\u003etrans\u003c/em\u003e \u0026beta;-carotene to 9-\u003cem\u003ecis\u003c/em\u003e \u0026beta;-carotene, which serves as a direct precursor (Tolnai et al., \u003cspan class=\"CitationRef\"\u003e2024\u003c/span\u003e). Figure \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e illustrates that the massive accumulation of \u0026beta;-carotene under RL and BL is attributed to their capability to markedly downregulate the genes related to \u0026beta;-carotene degradation \u003cem\u003e(LUT5\u003c/em\u003e, \u003cem\u003eABA2\u003c/em\u003e). Under RL and BL, the metabolic pathway from \u0026beta;-carotene to \u003cem\u003eABA\u003c/em\u003e is significantly inhibited, thereby reducing both the degradation and loss of \u0026beta;-carotene. Notably, while \u003cem\u003eABA1\u003c/em\u003e gene expression is significantly downregulated under BL, it undergoes a marked upregulation under RL. Research by Barrero et al. (\u003cspan class=\"CitationRef\"\u003e2008\u003c/span\u003e) indicates that \u003cem\u003eABA1\u003c/em\u003e gene expression is influenced by light intensity, and tends to be downregulated in strong light and upregulated in weak light or darkness. We propose that this may relate to the attenuation levels of RL and BL in aquatic environments: RL attenuates more rapidly than BL does (Siefermann-Harms, \u003cspan class=\"CitationRef\"\u003e1987\u003c/span\u003e). Consequently, a significant difference exists in \u003cem\u003eABA1\u003c/em\u003e gene expression within \u003cem\u003eD. salina\u003c/em\u003e cells under RL and BL of the same intensity. Furthermore, \u003cem\u003eLUT5\u003c/em\u003e and \u003cem\u003eABA2\u003c/em\u003e undergo greater downregulation under BL than under RL, indicating that BL exerts a stronger inhibitory effect on \u0026beta;-carotene metabolism than RL does. In this way, all-\u003cem\u003etrans\u003c/em\u003e \u0026beta;-carotene is prevented from converting into its biosynthetic precursor for \u003cem\u003eABA\u003c/em\u003e (9-\u003cem\u003ecis\u003c/em\u003e-\u0026beta;-carotene). The conversion process is suppressed more effectively under BL than under RL. As such, we observed an overall downregulation of the \u0026beta;-carotene metabolism pathway within \u003cem\u003eD. salina\u003c/em\u003e cells under BL\u0026mdash;this accounts for their higher content of all-\u003cem\u003etrans\u003c/em\u003e \u0026beta;-carotene under BL. Ultimately, through Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e, at the level of differential gene expression, we elucidate the mechanisms underlying substantial accumulation and activity variations of\u0026beta;-carotenoids induced by exposure to differing wavelengths of illumination, in \u003cem\u003eD. salina\u003c/em\u003e cells.\u003c/p\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eLight quality can regulate photosynthetic electron transport activity and gene expression in the β-carotene metabolism pathways in \u003cem\u003eD. salina\u003c/em\u003e. Ultimately, this regulation affects the growth of \u003cem\u003eD. salina\u003c/em\u003e, the accumulation of β-carotene, and the proportions of its cis isomers, namely 9-\u003cem\u003ecis\u003c/em\u003e carotene, 13-\u003cem\u003ecis\u003c/em\u003e carotene, and all-\u003cem\u003etrans\u003c/em\u003e β-carotene.\u003c/p\u003e\n\u003cp\u003eCompared to WL, monochromatic BL and monochromatic RL are more conducive to the accumulation of β-carotene in algae cells. Under BL, the content of all-\u003cem\u003etrans\u003c/em\u003e β-carotene is much higher, while under RL, the contents of 9-\u003cem\u003ecis\u003c/em\u003e carotene and 13-\u003cem\u003ecis\u003c/em\u003e carotene are elevated. Both BL and RL enhance the algal cells' capability to absorb light, increase the rate of photosynthetic electron transport, and reduce energy dissipation, thereby improving cellular photosynthetic efficiency and activity. Such effects help promote the energy conversion processes within algal cells, facilitating the synthesis and accumulation of carotenoids.\u003c/p\u003e\n\u003cp\u003eLight quality can regulate the accumulation of β-carotene in \u003cem\u003eD. salina\u0026nbsp;\u003c/em\u003eand its cis-isomerization levels. This is associated with both the upstream synthesis of β-carotene and the downstream degradation related to its conversion into abscisic acid (\u003cem\u003eABA\u003c/em\u003e). Two key genes involved in the β-carotene degradation pathway , \u003cem\u003eLUT5\u003c/em\u003e and \u003cem\u003eABA2\u003c/em\u003e, are significantly downregulated under BL and RL, resulting in a reduced breakdown of carotenoids within cells. The conversion from all-\u003cem\u003etrans\u003c/em\u003e β-carotene to the \u003cem\u003eABA\u003c/em\u003e biosynthetic precursor 9-\u003cem\u003ecis\u0026nbsp;\u003c/em\u003eβ-carotene is significantly inhibited under BL, leading to a higher degree of suppression in β-carotene metabolism. This explains why \u003cem\u003eD. salina\u003c/em\u003e produces a greater content of all-\u003cem\u003etrans\u003c/em\u003e β-carotene when exposed to BL.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eCredit authorship contribution statement\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTianze Zhao: Conceptualization, Supervision, Validation, Writing - review. Yongfu Li: Conceptualization, Investigation, Data curation. Xingkai Che: Investigation. Haixing Wu: Writing - editing. Yuchen Ye: Methodology. Dingning Fan: Software. Zhendong Li: Methodology. Yingjie Zhao: Methodology. Wei Ye: Methodology.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eStatement of informed consent, human/animal rights\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo conflicts, informed consent, human or animal rights applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of author agreement to authorship and submission\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll the authors declare that this manuscript is original, has not been published before, and is not currently being considered for publication elsewhere. All authors have approved the manuscript and agreed with its submission to the Ecotoxicology and Environmental Safety\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of competing interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have no conflict of interest. We claim that we have no commercial or associative interest relevant to the work that contributes to conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the Fundamental Research Funds for the Central Universities (B240201165), the National Natural Science Foundation of China (No. 42276189), the GEF Small Grants Programme China (CPR/DLF/IW/2023/03), the National Nonprofit Institute Research Grants of TIWTE (TKS20230304), and the Innovation and Entrepreneurship project for college students of Hohai University (202310294184Y).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData and materials will be made available on request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAmendola, S., Kneip, J. S., Meyer, F., Perozeni, F., Cazzaniga, S., Lauersen, K. J., Baier, T. (2023). Metabolic engineering for efficient ketocarotenoid accumulation in the green microalga \u003cem\u003eChlamydomonas reinhardtii\u003c/em\u003e. \u003cem\u003eACS Synthetic Biology\u003c/em\u003e, \u003cem\u003e12(3)\u003c/em\u003e, 820-831.\u003c/li\u003e\n \u003cli\u003eArnon, D. I. (1949). Copper enzymes in isolated chloroplasts. Polyphenoloxidase in Beta vulgaris. \u003cem\u003ePlant physiology\u003c/em\u003e, \u003cem\u003e24(1)\u003c/em\u003e, 1.\u003c/li\u003e\n \u003cli\u003eBarrero, J. M., Rodr\u0026iacute;guez, P. L., Quesada, V., AlabadI, D., Blazquez, M. A., BOUTIN, J. P.,\u0026nbsp;Micol, J. L. (2008). The ABA1 gene and carotenoid biosynthesis are required for late skotomorphogenic growth in \u003cem\u003eArabidopsis thaliana\u003c/em\u003e. \u003cem\u003ePlant, cell \u0026amp; environment\u003c/em\u003e, \u003cem\u003e31(2)\u003c/em\u003e, 227-234.\u003c/li\u003e\n \u003cli\u003eBen-Amotz, A. (1995). New mode of Dunaliella biotechnology: two-phase growth for \u0026beta;-carotene production. \u003cem\u003eJournal of applied phycology\u003c/em\u003e, \u003cem\u003e7\u003c/em\u003e, 65-68.\u003c/li\u003e\n \u003cli\u003eBen-Amotz, A., Shaish, A.,\u0026nbsp;Avron, M. (1989). Mode of action of the massively accumulated \u0026beta;-carotene of \u003cem\u003eDunaliella bardawil\u003c/em\u003e in protecting the alga against damage by excess irradiation. \u003cem\u003ePlant Physiology\u003c/em\u003e, \u003cem\u003e91(3)\u003c/em\u003e, 1040-1043.\u003c/li\u003e\n \u003cli\u003eBorowitzka, L. J.,\u0026nbsp;Borowitzka, M. A. (1989). \u0026beta;-carotene (provitamin A) production with algae. \u003cem\u003eIn Biotechnology of vitamins, pigments and growth factors\u003c/em\u003e (pp. 15-26). Dordrecht: Springer Netherlands.\u003c/li\u003e\n \u003cli\u003eBorowitzka, M. A. (1988). Algal growth media and sources of algal cultures. In \u003cem\u003eMicro-algal biotechnology\u003c/em\u003e (pp. 456-465). Cambridge University Press.\u003c/li\u003e\n \u003cli\u003eBorowitzka, M. A. (2013). Dunaliella: biology, production, and markets. \u003cem\u003eHandbook of microalgal culture: applied phycology and biotechnology\u003c/em\u003e, 359-368.\u003c/li\u003e\n \u003cli\u003eBustin, S. A., Beaulieu, J. F., Huggett, J., Jaggi, R., Kibenge, F. S., Olsvik, P. A.,\u0026nbsp;Toegel, S. (2010). MIQE precis: Practical implementation of minimum standard guidelines for fluorescence-based quantitative real-time PCR experiments. \u003cem\u003eBMC molecular biology\u003c/em\u003e, \u003cem\u003e11(1)\u003c/em\u003e, 1-5.\u003c/li\u003e\n \u003cli\u003eCapa-Robles, W., Garc\u0026iacute;a-Mendoza, E.,\u0026nbsp;Paniagua-Michel, J. D. J. (2021). Enhanced \u0026beta;-carotene and biomass production by induced mixotrophy in \u003cem\u003eDunaliella salina\u0026nbsp;\u003c/em\u003eacross a combined strategy of glycerol, salinity, and light. \u003cem\u003eMetabolites\u003c/em\u003e, \u003cem\u003e11(12)\u003c/em\u003e, 866.\u003c/li\u003e\n \u003cli\u003eChen, C. Y., Chen, Y. C., Huang, H. C., Ho, S. H.,\u0026nbsp;Chang, J. S. (2015). Enhancing the production of eicosapentaenoic acid (EPA) from \u003cem\u003eNannochloropsis oceanica\u003c/em\u003e CY2 using innovative photobioreactors with optimal light source arrangements. \u003cem\u003eBioresource technology\u003c/em\u003e, \u003cem\u003e191\u003c/em\u003e, 407-413.\u003c/li\u003e\n \u003cli\u003eChen, C. Y., Yeh, K. L., Aisyah, R., Lee, D. J.,\u0026nbsp;Chang, J. S. (2011). Cultivation, photobioreactor design and harvesting of microalgae for biodiesel production: a critical review. \u003cem\u003eBioresource technology\u003c/em\u003e,\u003cem\u003e\u0026nbsp;102(1)\u003c/em\u003e, 71-81.\u003c/li\u003e\n \u003cli\u003eChen, H. H., Liang, M. H., Ye, Z. W., Zhu, Y. H.,\u0026nbsp;Jiang, J. G. (2023). Engineering the \u0026beta;-carotene metabolic pathway of microalgae Dunaliella to confirm its carotenoid synthesis pattern in comparison to bacteria and plants.\u003cem\u003e\u0026nbsp;Microbiology Spectrum\u003c/em\u003e, \u003cem\u003e11(2)\u003c/em\u003e, e04361-22.\u003c/li\u003e\n \u003cli\u003eChen, X., Khadiwada, J. R., Chio, C., Shrestha, S., Kognou, A. L. M., Fan, L.,\u0026nbsp;Qin, W. (2024). Low-cost cultivation of \u003cem\u003eNannochloropsis oceanica\u003c/em\u003e in newly designed photobioreactors and its productivity trends in semi-continuous cultivation under inland outdoor conditions. \u003cem\u003eBioresource Technology\u003c/em\u003e,\u0026nbsp;\u003cem\u003e402\u003c/em\u003e,\u0026nbsp;130829.\u003c/li\u003e\n \u003cli\u003eCrepin, A.,\u0026nbsp;Caffarri, S. (2018). Functions and evolution of Lhcb isoforms composing LHCII, the major light harvesting complex of photosystem II of green eukaryotic organisms. \u003cem\u003eCurrent Protein and Peptide Science\u003c/em\u003e, \u003cem\u003e19(7)\u003c/em\u003e, 699-713.\u003c/li\u003e\n \u003cli\u003eDall\u0026apos;Osto, L., Lico, C., Alric, J., Giuliano, G., Havaux, M.,\u0026nbsp;Bassi, R. (2006). Lutein is needed for efficient chlorophyll triplet quenching in the major LHCII antenna complex of higher plants and effective photoprotection in vivo under strong light. \u003cem\u003eBMC plant biology\u003c/em\u003e, \u003cem\u003e6\u003c/em\u003e, 1-20.\u003c/li\u003e\n \u003cli\u003eDanesh, A. F., Ebrahimi, S., Salehi, A.,\u0026nbsp;Parsa, A. (2017). Impact of nutrient starvation on intracellular biochemicals and calorific value of mixed microalgae. \u003cem\u003eBiochemical Engineering Journal\u003c/em\u003e, \u003cem\u003e125\u003c/em\u003e, 56-64.\u003c/li\u003e\n \u003cli\u003eDel-Campo, J. A., Garc\u0026iacute;a-Gonz\u0026aacute;lez, M.,\u0026nbsp;Guerrero, M. G. (2007). Outdoor cultivation of microalgae for carotenoid production: current state and perspectives. \u003cem\u003eApplied microbiology and biotechnology\u003c/em\u003e, \u003cem\u003e74\u003c/em\u003e, 1163-1174.\u003c/li\u003e\n \u003cli\u003eD\u0026iacute;az, J. P., Inostroza, C.,\u0026nbsp;Aci\u0026eacute;n, F. G. (2021). Scale-up of a Fibonacci-Type Photobioreactor for the Production of\u003cem\u003e\u0026nbsp;Dunaliella salina\u003c/em\u003e. \u003cem\u003eApplied Biochemistry and Biotechnology\u003c/em\u003e, \u003cem\u003e193\u003c/em\u003e, 188-204.\u003c/li\u003e\n \u003cli\u003eFiedor, J.,\u0026nbsp;Burda, K. (2014). Potential role of carotenoids as antioxidants in human health and disease. \u003cem\u003eNutrients\u003c/em\u003e,\u003cem\u003e\u0026nbsp;6(2)\u003c/em\u003e, 466-488.\u003c/li\u003e\n \u003cli\u003eFu, W., Gu\u0026eth;mundsson, \u0026Oacute;., Paglia, G., Herj\u0026oacute;lfsson, G., Andr\u0026eacute;sson, \u0026Oacute;. S., Palsson, B. \u0026Oslash;.,\u0026nbsp;Brynj\u0026oacute;lfsson, S. (2013). Enhancement of carotenoid biosynthesis in the green microalga \u003cem\u003eDunaliella salina\u003c/em\u003e with light-emitting diodes and adaptive laboratory evolution. \u003cem\u003eApplied microbiology and biotechnology\u003c/em\u003e, \u003cem\u003e97\u003c/em\u003e, 2395-2403.\u003c/li\u003e\n \u003cli\u003eG\u0026oacute;mez, P. I.,\u0026nbsp;Gonz\u0026aacute;lez, M. A. (2005). The effect of temperature and irradiance on the growth and carotenogenic capacity of seven strains of \u003cem\u003eDunaliella salina\u003c/em\u003e (Chlorophyta) cultivated under laboratory conditions. \u003cem\u003eBiological research\u003c/em\u003e, \u003cem\u003e38(2-3)\u003c/em\u003e, 151-162.\u003c/li\u003e\n \u003cli\u003eGorai, T., Katayama, T., Obata, M., Murata, A.,\u0026nbsp;Taguchi, S. (2014). Low blue light enhances growth rate, light absorption, and photosynthetic characteristics of four marine phytoplankton species. \u003cem\u003eJournal of experimental marine biology and ecology\u003c/em\u003e,\u003cem\u003e\u0026nbsp;459\u003c/em\u003e, 87-95.\u003c/li\u003e\n \u003cli\u003eGötz, T., Windhövel, U., Böger, P.,\u0026nbsp;Sandmann, G. (1999). Protection of photosynthesis against ultraviolet-B radiation by carotenoids in transformants of the \u003cem\u003ecyanobacterium Synechococcus\u003c/em\u003e PCC7942. \u003cem\u003ePlant Physiology\u003c/em\u003e,\u0026nbsp;\u003cem\u003e120(2)\u003c/em\u003e, 599-604.\u003c/li\u003e\n \u003cli\u003eGreenberger, S., Harats, D., Salameh, F., Lubish, T., Harari, A., Trau, H.,\u0026nbsp;Shaish, A. (2012). 9-cis\u0026ndash;rich \u0026beta;-carotene powder of the alga Dunaliella reduces the severity of chronic plaque psoriasis: a randomized, double-blind, placebo-controlled clinical trial. \u003cem\u003eJournal of the American College of Nutrition\u003c/em\u003e, \u003cem\u003e31(5)\u003c/em\u003e, 320-326.\u003c/li\u003e\n \u003cli\u003eGrune, T., Lietz, G., Palou, A., Ross, A. C., Stahl, W., Tang, G.,\u0026nbsp;Biesalski, H. K. (2010). \u0026beta;-Carotene is an important vitamin A source for humans. \u003cem\u003eThe Journal of nutrition\u003c/em\u003e, \u003cem\u003e140(12)\u003c/em\u003e, 2268S-2285S.\u003c/li\u003e\n \u003cli\u003eGuermazi, W., Masmoudi, S., Trabelsi, N. A., Gammoudi, S., Ayadi, H., Morant-Manceau, A.,\u0026nbsp;Hotos, G. N. (2023). Physiological and biochemical responses in microalgae \u003cem\u003eDunaliella salina\u003c/em\u003e, \u003cem\u003eCylindrotheca closterium\u003c/em\u003e and \u003cem\u003ePhormidium versicolor\u003c/em\u003e NCC466 exposed to high salinity and irradiation. \u003cem\u003eLife\u003c/em\u003e, \u003cem\u003e13(2)\u003c/em\u003e, 313.\u003c/li\u003e\n \u003cli\u003eHarari, A., Harats, D., Marko, D., Cohen, H., Barshack, I., Gonen, A.,\u0026nbsp;Shaish, A. (2013). Supplementation with 9-cis \u0026beta;-carotene-rich alga Dunaliella improves hyperglycemia and adipose tissue inflammation in diabetic mice. \u003cem\u003eJournal of applied phycology\u003c/em\u003e, \u003cem\u003e25\u003c/em\u003e, 687-693.\u003c/li\u003e\n \u003cli\u003eHarvey, P. J.,\u0026nbsp;Ben-Amotz, A. (2020). Towards a sustainable \u003cem\u003eDunaliella salina\u003c/em\u003e microalgal biorefinery for 9-cis \u0026beta;-carotene production. \u003cem\u003eAlgal Research\u003c/em\u003e, \u003cem\u003e50\u003c/em\u003e, 102002.\u003c/li\u003e\n \u003cli\u003eHejazi, M. A., Holwerda, E.,\u0026nbsp;Wijffels, R. H. (2004). Milking microalga \u003cem\u003eDunaliella salina\u003c/em\u003e for \u0026beta;‐carotene production in two‐phase bioreactors. \u003cem\u003eBiotechnology and bioengineering\u003c/em\u003e, \u003cem\u003e85(5)\u003c/em\u003e, 475-481.\u003c/li\u003e\n \u003cli\u003eHonda, M. (2021). Carotenoid isomers: A systematic review of the analysis, biological activity, physicochemical property, and methods for isomerization. \u003cem\u003eStudies in natural products chemistry\u003c/em\u003e,\u003cem\u003e\u0026nbsp;68\u003c/em\u003e, 173-220.\u003c/li\u003e\n \u003cli\u003eHuang, Z., Zong, M. H., Wang, J., Peng, S. Y., Yu, M.,\u0026nbsp;Lou, W. Y. (2024). Structural and interfacial properties of acetylated \u003cem\u003eMillettia speciosa\u003c/em\u003e Champ polysaccharide and stability evaluation of the resultant O/W emulsion containing \u0026beta;-carotene. \u003cem\u003eInternational Journal of Biological Macromolecules\u003c/em\u003e, \u003cem\u003e264\u003c/em\u003e, 130556.\u003c/li\u003e\n \u003cli\u003eJia, K. P., Mi, J., Ali, S., Ohyanagi, H., Moreno, J. C., Ablazov, A.,\u0026nbsp;Al-Babili, S. (2022). An alternative, zeaxanthin epoxidase-independent abscisic acid biosynthetic pathway in plants. \u003cem\u003eMolecular Plant\u003c/em\u003e, \u003cem\u003e15(1)\u003c/em\u003e, 151-166.\u003c/li\u003e\n \u003cli\u003eJohnsen, G.,\u0026nbsp;Sakshaug, E. (2007). Biooptical characteristics of PSII and PSI in 33 species (13 pigment groups) of marine phytoplankton, and the relevance for pulse‐amplitude‐modulated and fast‐repetition‐rate fluorometry 1. \u003cem\u003eJournal of Phycology\u003c/em\u003e,\u003cem\u003e\u0026nbsp;43(6)\u003c/em\u003e, 1236-1251.\u003c/li\u003e\n \u003cli\u003eKevin, K.,\u0026nbsp;Widjaja, A. (2023). Effect of nitrogen deficiency and UV light on \u003cem\u003eDunaliella salina\u003c/em\u003e \u0026beta;-carotene production. \u003cem\u003eIn AIP Conference Proceedings\u003c/em\u003e (Vol. 2847, No. 1). AIP Publishing.\u003c/li\u003e\n \u003cli\u003eKim, M., Kim, J., Lee, S., Khanh, N., Li, Z., Polle, J. E.,\u0026nbsp;Jin, E. (2024). Deciphering the \u0026beta;‐carotene hyperaccumulation in Dunaliella by the comprehensive analysis of \u003cem\u003eDunaliella salina\u003c/em\u003e and \u003cem\u003eDunaliella tertiolecta\u003c/em\u003e under high light conditions. \u003cem\u003ePlant, Cell \u0026amp; Environment\u003c/em\u003e, \u003cem\u003e47(1)\u003c/em\u003e, 213-229.\u003c/li\u003e\n \u003cli\u003eLam, M. K., Lee, K. T. (2014). Scale-up and commercialization of\u0026nbsp;algal cultivation and biofuel production.\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003cem\u003eBiofuels from algae\u003c/em\u003e. Elsevier, Amsterdam, pp 261-286.\u003c/li\u003e\n \u003cli\u003eLamers, P. P., van de Laak, C. C., Kaasenbrood, P. S., Lorier, J., Janssen, M., De Vos, R. C.,\u0026nbsp;Wijffels, R. H. (2010). Carotenoid and fatty acid metabolism in light‐stressed \u003cem\u003eDunaliella salina\u003c/em\u003e. \u003cem\u003eBiotechnology and bioengineering\u003c/em\u003e, \u003cem\u003e106(4)\u003c/em\u003e, 638-648.\u003c/li\u003e\n \u003cli\u003eLan, Y., Song, Y., Guo, Y., Qiao, D., Cao, Y.,\u0026nbsp;Xu, H. (2022). DsLCYB Directionally Modulated \u0026beta;-Carotene of the Green Alga \u003cem\u003eDunaliella salina\u003c/em\u003e under Red Light Stress. \u003cem\u003eJournal of Microbiology and Biotechnology\u003c/em\u003e, \u003cem\u003e32(12)\u003c/em\u003e, 1622.\u003c/li\u003e\n \u003cli\u003eLehmuskero, A., Chauton, M. S.,\u0026nbsp;Bostr\u0026ouml;m, T. (2018). Light and photosynthetic microalgae: A review of cellular-and molecular-scale optical processes. \u003cem\u003eProgress in oceanography\u003c/em\u003e, \u003cem\u003e168\u003c/em\u003e, 43-56.\u003c/li\u003e\n \u003cli\u003eLeo, M. A.,\u0026nbsp;Lieber, C. S. (1999). Alcohol, vitamin A, and \u0026beta;-carotene: adverse interactions, including hepatotoxicity and carcinogenicity. \u003cem\u003eThe American journal of clinical nutrition\u003c/em\u003e, \u003cem\u003e69(6)\u003c/em\u003e, 1071-1085.\u003c/li\u003e\n \u003cli\u003eLi, J. W., Zhou, P., Deng, Y. J., Hu, Z. H., Li, X. H., Chen, X.,\u0026nbsp;Zhuang, J. (2023). Overexpressing CsPSY1 Gene of Tea Plant, Encoding a Phytoene Synthase, Improves \u0026alpha;-Carotene and \u0026beta;-Carotene Contents in Carrot. \u003cem\u003eMolecular Biotechnology\u003c/em\u003e, 1-12.\u003c/li\u003e\n \u003cli\u003eLi, Y. F.,\u0026nbsp;Meng, F. P. (2014). Type selection of transparent plate for microalgae photo-bioreactor building based on light transmissivity analysis. \u003cem\u003eActa Opt Sin\u003c/em\u003e, \u003cem\u003e1\u003c/em\u003e, 0123003-0123006.\u003c/li\u003e\n \u003cli\u003eLi, Y., Cai, X., Gu, W.,\u0026nbsp;Wang, G. (2020a). Transcriptome analysis of carotenoid biosynthesis in \u003cem\u003eDunaliella salina\u003c/em\u003e under red and blue light. \u003cem\u003eJournal of Oceanology and Limnology\u003c/em\u003e, \u003cem\u003e38(1)\u003c/em\u003e, 177-185.\u003c/li\u003e\n \u003cli\u003eLi, Y., Li, L., Liu, J.,\u0026nbsp;Qin, R. (2020b). Light absorption and growth response of Dunaliella under different light qualities. \u003cem\u003eJournal of applied phycology\u003c/em\u003e, \u003cem\u003e32\u003c/em\u003e, 1041-1052.\u003c/li\u003e\n \u003cli\u003eLi, Y.,\u0026nbsp;Liu, J. (2020). Analysis of light absorption and photosynthetic activity by \u003cem\u003eIsochrysis galbana\u003c/em\u003e under different light qualities. \u003cem\u003eAquaculture research\u003c/em\u003e, \u003cem\u003e51(7)\u003c/em\u003e, 2893-2902.\u003c/li\u003e\n \u003cli\u003eLi, Y., Zhao, T., Qin, M., Che, X.,\u0026nbsp;Zhang, A. (2024). Toxicity of the sunscreen UV filter benzophenone-3 (OBZ) to the microalga \u003cem\u003eSelenastrum capricornutum\u003c/em\u003e: An insight into OBZ\u0026rsquo;s damage to photosynthesis and respiration. \u003cem\u003eEcotoxicology and Environmental Safety\u003c/em\u003e, \u003cem\u003e278\u003c/em\u003e, 116441.\u003c/li\u003e\n \u003cli\u003eLiang, M. H., Xie, S. R., Dai, J. L., Chen, H. H.,\u0026nbsp;Jiang, J. G. (2023). Roles of two phytoene synthases and orange protein in carotenoid metabolism of the \u0026beta;-carotene-accumulating \u003cem\u003eDunaliella salina\u003c/em\u003e. \u003cem\u003eMicrobiology Spectrum\u003c/em\u003e, \u003cem\u003e11(3)\u003c/em\u003e, e00069-23.\u003c/li\u003e\n \u003cli\u003eLima, S., Schulze, P. S., Sch\u0026uuml;ler, L. M., Rautenberger, R., Morales-S\u0026aacute;nchez, D., Santos, T. F.,\u0026nbsp;Kiron, V. (2021). Flashing light emitting diodes (LEDs) induce proteins, polyunsaturated fatty acids and pigments in three microalgae. \u003cem\u003eJournal of Biotechnology\u003c/em\u003e, \u003cem\u003e325\u003c/em\u003e, 15-24.\u003c/li\u003e\n \u003cli\u003eMa, C., Qu, W., Ho, S. H., Li, J., Li, F.,\u0026nbsp;Yi, L. (2024). Effects of microalgal (\u003cem\u003eTetradesmus obliquus\u003c/em\u003e MCX38) attachment on photobioreactor treatment efficiency of raw swine wastewater.\u003cem\u003e\u0026nbsp;Bioresource Technology\u003c/em\u003e,\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003cem\u003e403\u003c/em\u003e,\u0026nbsp;130866.\u003c/li\u003e\n \u003cli\u003eMazzucchi, L., Xu, Y.,\u0026nbsp;Harvey, P. (2020). Stereoisomers of colourless carotenoids from the marine microalga \u003cem\u003eDunaliella salina\u003c/em\u003e. \u003cem\u003eMolecules\u003c/em\u003e, \u003cem\u003e25(8)\u003c/em\u003e, 1880.\u003c/li\u003e\n \u003cli\u003eMirzaie, M. M., Lak, Z. J.,\u0026nbsp;Meybodi, F. H. (2021). A new shifting strategy in flashing light based on the cell growth curve to enhance \u0026beta;-carotene biosynthesis in \u003cem\u003eDunaliella salina\u003c/em\u003e. \u003cem\u003eCurrent Microbiology\u003c/em\u003e, \u003cem\u003e78(7)\u003c/em\u003e, 2733-2740.\u003c/li\u003e\n \u003cli\u003eMizobuchi, K., Hayashi, T., Ueno, S., Kondo, M., Terasaki, H., Aoki, T.,\u0026nbsp;Nakano, T. (2023). One-Year Outcomes of Oral Treatment With Alga Capsules Containing Low Levels of 9-cis-\u0026beta;-Carotene in RDH5-Related Fundus Albipunctatus. \u003cem\u003eAmerican Journal of Ophthalmology\u003c/em\u003e, \u003cem\u003e254\u003c/em\u003e, 193-202.\u003c/li\u003e\n \u003cli\u003eMohebi Najafabadi, M.,\u0026nbsp;Naeimpoor, F. (2023). Boosting \u0026beta;-carotene and storage materials productivities by two-stage mixed and monochromatic exposure stresses on\u003cem\u003e\u0026nbsp;Dunaliella salina\u003c/em\u003e. \u003cem\u003eInternational Journal of Phytoremediation\u003c/em\u003e, 25(5), 609-620.\u003c/li\u003e\n \u003cli\u003eMoheimani, N. R.,\u0026nbsp;Parlevliet, D. (2013). Sustainable solar energy conversion to chemical and electrical energy. \u003cem\u003eRenewable and Sustainable Energy Reviews\u003c/em\u003e,\u003cem\u003e\u0026nbsp;27\u003c/em\u003e, 494-504.\u003c/li\u003e\n \u003cli\u003eMolina-Miras, A., L\u0026oacute;pez-Rosales, L., S\u0026aacute;nchez-Mir\u0026oacute;n, A., Cer\u0026oacute;n-Garc\u0026iacute;a, M. C., Seoane-Parra, S., Garc\u0026iacute;a-Camacho, F.,\u0026nbsp;Molina-Grima, E. (2018). Long-term culture of the marine dinoflagellate microalga \u003cem\u003eAmphidinium carterae\u003c/em\u003e in an indoor LED-lighted raceway photobioreactor: Production of carotenoids and fatty acids. \u003cem\u003eBioresource technology\u003c/em\u003e, \u003cem\u003e265\u003c/em\u003e, 257-267.\u003c/li\u003e\n \u003cli\u003eMurthy, K. C., Vanitha, A., Rajesha, J., Swamy, M. M., Sowmya, P. R., Ravishankar, G. A. (2005). In vivo antioxidant activity of carotenoids from \u003cem\u003eDunaliella salina\u003c/em\u003e\u0026mdash;a green microalga. \u003cem\u003eLife sciences\u003c/em\u003e, \u003cem\u003e76(12)\u003c/em\u003e, 1381-1390.\u003c/li\u003e\n \u003cli\u003eNational Standardization Technical Committee (2008) Standard illuminants and geometric conditions GB/T 3978-2008. \u003cem\u003eChina Standard Press\u003c/em\u003e, Beijing.\u003c/li\u003e\n \u003cli\u003ePapaioannou, E. H.,\u0026nbsp;Liakopoulou-Kyriakides, M. (2012). Agro-food wastes utilization by \u003cem\u003eBlakeslea trispora\u0026nbsp;\u003c/em\u003efor carotenoids production. \u003cem\u003eActa Biochimica Polonica\u003c/em\u003e, \u003cem\u003e59(1)\u003c/em\u003e, 151-153.\u003c/li\u003e\n \u003cli\u003ePrieto, A., Ca\u0026ntilde;avate, J. P.,\u0026nbsp;Garc\u0026iacute;a-Gonz\u0026aacute;lez, M. (2011). Assessment of carotenoid production by \u003cem\u003eDunaliella salina\u003c/em\u003e in different culture systems and operation regimes. \u003cem\u003eJournal of biotechnology\u003c/em\u003e, \u003cem\u003e151(2)\u003c/em\u003e, 180-185.\u003c/li\u003e\n \u003cli\u003ePriscilla, K., Sharma, V., Gautam, A., Gupta, P., Dagar, R., Kishore, V.,\u0026nbsp;Kumar, R. (2024). Carotenoid Extraction from Plant Tissues. In \u003cem\u003ePlant Functional Genomics: Methods and Protocols\u003c/em\u003e, Volume 2 (pp. 3-18). New York, NY: Springer US.\u003c/li\u003e\n \u003cli\u003ePulz, O.,\u0026nbsp;Gross, W. (2004). Valuable products from biotechnology of microalgae. \u003cem\u003eApplied microbiology and biotechnology\u003c/em\u003e, \u003cem\u003e65\u003c/em\u003e, 635-648.\u003c/li\u003e\n \u003cli\u003eQin, R., Li, Y., Zhang, L.,\u0026nbsp;Liu, J. (2021). The effect of salinity shock on the growth and rapid light curve of\u0026nbsp;\u003cem\u003eD\u003c/em\u003e\u003cem\u003eunaliella salina\u003c/em\u003e. \u003cem\u003eAquaculture Research\u003c/em\u003e, \u003cem\u003e52(6)\u003c/em\u003e, 2569-2579.\u003c/li\u003e\n \u003cli\u003eRasband, W. S. (2012). ImageJ: Image processing and analysis in Java. \u003cem\u003eAstrophysics Source Code Library\u003c/em\u003e, ascl-1206.\u003c/li\u003e\n \u003cli\u003eRelevy, N. Z., R\u0026uuml;hl, R., Harari, A., Grosskopf, I., Barshack, I., Ben-Amotz, A.,\u0026nbsp;Shaish, A. (2015). 9-cis \u0026beta;-Carotene inhibits atherosclerosis development in female LDLR-/-mice. \u003cem\u003eFunctional Foods in Health and Disease\u003c/em\u003e, \u003cem\u003e5(2)\u003c/em\u003e, 67-79.\u003c/li\u003e\n \u003cli\u003eRodr\u0026iacute;guez-Bola\u0026ntilde;os, M., Vargas-Romero, G., Jaguer-Garc\u0026iacute;a, G., Aguilar-Gonzalez, Z. I., Lagos-Romero, V.,\u0026nbsp;Miranda-Astudillo, H. V. (2024). Antares I: a Modular Photobioreactor Suitable for Photosynthesis and Bioenergetics Research. \u003cem\u003eApplied Biochemistry and Biotechnology\u003c/em\u003e, \u003cem\u003e196(4)\u003c/em\u003e, 2176-2195.\u003c/li\u003e\n \u003cli\u003eRozenberg, J. M., Sorokin, B. A., Mukhambetova, A. N., Emelianova, A. A., Kuzmin, V. V., Belogurova‐Ovchinnikova, O. Y.,\u0026nbsp;Kuzmin, D. V. (2024). Recent advances and fundamentals of microalgae cultivation technology. \u003cem\u003eBiotechnology Journal\u003c/em\u003e, \u003cem\u003e19(3)\u003c/em\u003e, 2300725.\u003c/li\u003e\n \u003cli\u003eSathasivam, R.,\u0026nbsp;Ki, J. S. (2019). Differential transcriptional responses of carotenoid biosynthesis genes in the marine green alga \u003cem\u003eTetraselmis suecica\u003c/em\u003e exposed to redox and non-redox active metals. \u003cem\u003eMolecular biology reports\u003c/em\u003e, \u003cem\u003e46(1)\u003c/em\u003e, 1167-1179.\u003c/li\u003e\n \u003cli\u003eSiefermann‐Harms, D. (1987). The light‐harvesting and protective functions of carotenoids in photosynthetic membranes. \u003cem\u003ePhysiologia Plantarum\u003c/em\u003e, \u003cem\u003e69(3)\u003c/em\u003e, 561-568.\u003c/li\u003e\n \u003cli\u003eSong, Y., Teakle, G.,\u0026nbsp;Lillywhite, R. (2023). Unravelling effects of red/far-red light on nutritional quality and the role and mechanism in regulating lycopene synthesis in postharvest cherry tomatoes. \u003cem\u003eFood Chemistry\u003c/em\u003e, \u003cem\u003e414\u003c/em\u003e, 135690.\u003c/li\u003e\n \u003cli\u003eStrasser, B., Strasser, R. (1995). Measuring fast fluorescence transients to address environmental questions: The JIP test. In Photosynthesis: From Light to Biosphere (Edited by P. Mathis), pp. 977-980. \u003cem\u003eKluwer Academic\u003c/em\u003e,\u003cem\u003e\u0026nbsp;Dordrecht\u003c/em\u003e.\u003c/li\u003e\n \u003cli\u003eSui, Y., Mazzucchi, L., Acharya, P., Xu, Y., Morgan, G.,\u0026nbsp;Harvey, P. J. (2021). A Comparison of \u0026beta;-Carotene, Phytoene and Amino Acids Production in \u003cem\u003eDunaliella salina\u003c/em\u003e DF 15 (CCAP 19/41) and \u003cem\u003eDunaliella salina\u003c/em\u003e CCAP 19/30 Using Different Light Wavelengths. \u003cem\u003eFoods\u003c/em\u003e, \u003cem\u003e10(11)\u003c/em\u003e, 2824.\u003c/li\u003e\n \u003cli\u003eSui, Y., Muys, M., Van de Waal, D. B., D\u0026apos;Adamo, S., Vermeir, P., Fernandes, T. V.,\u0026nbsp;Vlaeminck, S. E. (2019). Enhancement of co-production of nutritional protein and carotenoids in \u003cem\u003eDunaliella salina\u003c/em\u003e using a two-phase cultivation assisted by nitrogen level and light intensity. \u003cem\u003eBioresource technology\u003c/em\u003e, \u003cem\u003e287\u003c/em\u003e, 121398.\u003c/li\u003e\n \u003cli\u003eTolnai, Z., Sharma, H.,\u0026nbsp;So\u0026oacute;s, V. (2024). D27-like carotenoid isomerases: at the crossroads of strigolactone and abscisic acid biosynthesis. \u003cem\u003eJournal of Experimental Botany\u003c/em\u003e, \u003cem\u003e75(4)\u003c/em\u003e, 1148-1158.\u003c/li\u003e\n \u003cli\u003eTredici, M. R. (2004). Mass production of microalgae: photobioreactors. \u003cem\u003eHandbook of microalgal culture: Biotechnology and applied phycology\u003c/em\u003e, \u003cem\u003e1\u003c/em\u003e, 178-214.\u003c/li\u003e\n \u003cli\u003eUeno, Y., Aikawa, S., Kondo, A.,\u0026nbsp;Akimoto, S. (2019). Adaptation of light-harvesting functions of unicellular green algae to different light qualities. \u003cem\u003ePhotosynthesis research\u003c/em\u003e, \u003cem\u003e139\u003c/em\u003e, 145-154.\u003c/li\u003e\n \u003cli\u003eWagner, I., Steinweg, C.,\u0026nbsp;Posten, C. (2016). Mono‐and dichromatic LED illumination leads to enhanced growth and energy conversion for high‐efficiency cultivation of microalgae for application in space. \u003cem\u003eBiotechnology journal\u003c/em\u003e, \u003cem\u003e11(8)\u003c/em\u003e, 1060-1071.\u003c/li\u003e\n \u003cli\u003eWang, X. D., Krinsky, N. I., Benotti, P. N.,\u0026nbsp;Russell, R. M. (1994). Biosynthesis of 9-cis-retinoic acid from 9-cis-\u0026beta;-carotene in human intestinal mucosa \u003cem\u003ein vitro\u003c/em\u003e. \u003cem\u003eArchives of Biochemistry and Biophysics\u003c/em\u003e, \u003cem\u003e313(1)\u003c/em\u003e, 150-155.\u003c/li\u003e\n \u003cli\u003eWang, Z., Gerstein, M.,\u0026nbsp;Snyder, M. (2009). RNA-Seq: a revolutionary tool for transcriptomics. \u003cem\u003eNature reviews genetics\u003c/em\u003e, \u003cem\u003e10(1)\u003c/em\u003e, 57-63.\u003c/li\u003e\n \u003cli\u003eXi, Y., Xue, S., Cao, X., Chi, Z.,\u0026nbsp;Wang, J. (2021). Quantitative analysis on photon numbers received per cell for triggering \u0026beta;-carotene accumulation in \u003cem\u003eDunaliella salina\u003c/em\u003e. \u003cem\u003eBioresources and Bioprocessing\u003c/em\u003e, \u003cem\u003e8\u003c/em\u003e, 1-11.\u003c/li\u003e\n \u003cli\u003eXu, Y.,\u0026nbsp;Harvey, P. J. (2019). Red light control of \u0026beta;-carotene isomerisation to 9-cis \u0026beta;-carotene and carotenoid accumulation in \u003cem\u003eDunaliella salina\u003c/em\u003e. \u003cem\u003eAntioxidants\u003c/em\u003e,\u003cem\u003e\u0026nbsp;8(5)\u003c/em\u003e, 148.\u003c/li\u003e\n \u003cli\u003eYe, Z. W., Jiang, J. G., Wu, G. H. (2008). Biosynthesis and regulation of carotenoids in Dunaliella: progresses and prospects. \u003cem\u003eBiotechnology advances\u003c/em\u003e, \u003cem\u003e26(4)\u003c/em\u003e, 352-360.\u003c/li\u003e\n \u003cli\u003eZhao, Y., Wang, J., Zhang, H., Yan, C.,\u0026nbsp;Zhang, Y. (2013). Effects of various LED light wavelengths and intensities on microalgae-based simultaneous biogas upgrading and digestate nutrient reduction process. \u003cem\u003eBioresource technology\u003c/em\u003e, \u003cem\u003e136\u003c/em\u003e, 461-468.\u003c/li\u003e\n \u003cli\u003eZhao, Y., Yang, X., Hu, Y., Gu, Q., Chen, W., Li, J.,\u0026nbsp;Liu, Y. (2021). Evaluation of carotenoids accumulation and biosynthesis in two genotypes of pomelo (Citrus maxima) during early fruit development. \u003cem\u003eMolecules\u003c/em\u003e, \u003cem\u003e26(16)\u003c/em\u003e, 5054.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":false,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"","identity":"journal-of-applied-phycology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"10811","submissionUrl":"https://submission.nature.com/new-submission/10811/3","title":"Journal of Applied Phycology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Dunaliella salina, light quality, photosynthesis, Chl a fluorescence transient, all-trans β-carotene","lastPublishedDoi":"10.21203/rs.3.rs-5450150/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5450150/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eLight quality is a crucial abiotic environmental factor that influences the growth and β-carotene accumulation on \u003cem\u003eDunaliella salina\u003c/em\u003e. However, the influence of the factor on the primary photochemical reactions of \u003cem\u003eD. salina\u003c/em\u003e and the physiological mechanisms regulating β-carotene metabolism remains unclear at present. This study involved the batch culture of \u003cem\u003eD. salina\u003c/em\u003e using low light (40 ± 5 μmol photons m\u003csup\u003e-2\u003c/sup\u003e s\u003csup\u003e-1\u003c/sup\u003e, without inhibiting photosynthetic electron transfer) provided by different colored LEDs. Our results indicated that the growth rate, chlorophyll a/chlorophyll b/β-carotene content of \u003cem\u003eD. salina\u003c/em\u003e cells were higher under BL and RL than under WL and GL. The light absorption rates of chloroplasts in algae cells under BL and RL (22.8% and 18.6%, respectively) were higher than those under WL and GL (14.0% and 10.2%, respectively), which was attributed to the reduced light energy dissipation and increased photochemical efficiency under BL and RL. BL and RL enhanced the photosynthetic efficiency and β-carotene synthesis capability of \u003cem\u003eD. salina\u003c/em\u003e cells. It was observed that under low light, light quality has little influence on the synthesis process of β-carotene. However, two key genes involved in the degradation pathway of β-carotene (\u003cem\u003eLUT5\u003c/em\u003e and \u003cem\u003eABA2\u003c/em\u003e) are significantly downregulated under both BL and RL. The higher content of all-trans β-carotene under BL than under RL. This is attributed to the inhibition of the conversion pathway from all-\u003cem\u003etrans\u003c/em\u003e β-carotene to ABA biosynthesis precursor (9-\u003cem\u003ecis\u003c/em\u003e-β-carotene) is more pronounced under BL than under RL. This explains why\u003cem\u003e D.salina\u003c/em\u003e has a higher content of all-\u003cem\u003etrans\u003c/em\u003e β-carotene under BL, while synthesized more 9-\u003cem\u003ecis\u003c/em\u003e-β-carotene under RL.\u003c/p\u003e","manuscriptTitle":"Effects of monochromatic LED light qualities on the photosynthetic capacity and pigment content of Dunaliella salina","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-12-18 14:16:29","doi":"10.21203/rs.3.rs-5450150/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-01-30T00:52:39+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-01-27T21:53:02+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"105172514825398745822312618233758782865","date":"2025-01-06T16:04:01+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-01-02T05:55:56+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"246221328740215689768476243918483008422","date":"2024-12-05T10:11:32+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-11-18T05:01:41+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-11-18T04:47:54+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-11-18T04:22:42+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Applied Phycology","date":"2024-11-14T01:42:58+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"","identity":"journal-of-applied-phycology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"10811","submissionUrl":"https://submission.nature.com/new-submission/10811/3","title":"Journal of Applied Phycology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"d580c885-6992-4136-8318-1ba093ad9ffe","owner":[],"postedDate":"December 18th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-03-14T23:53:06+00:00","versionOfRecord":[],"versionCreatedAt":"2024-12-18 14:16:29","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5450150","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5450150","identity":"rs-5450150","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}