Effect of Seasonal Dynamics in Water Temperature and Electrical Conductivity on β- Carotene Biosynthesis in Green Spinach (Silver-beet) and Lettuce (Locarno) Leaves from Aquaponic Greenhouse

Effect of Seasonal Dynamics in Water Temperature and Electrical Conductivity on β- Carotene Biosynthesis in Green Spinach (Silver-beet) and Lettuce (Locarno) Leaves from Aquaponic Greenhouse | 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 Effect of Seasonal Dynamics in Water Temperature and Electrical Conductivity on β- Carotene Biosynthesis in Green Spinach (Silver-beet) and Lettuce (Locarno) Leaves from Aquaponic Greenhouse Labaran Ibrahim This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5898385/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The present study was conducted to determine the effects of seasonal dynamics in water temperature (WT) and electrical conductivity (EC) on β-Carotene biosynthesis in green spinach (GRSP) (Silver-beet) and green lettuce (GRLE) (Locarno) leaves from an aquaponic greenhouse. The WT and EC of the fish water tap (FWTP) and deep-water culture tank (DWCT) were assessed with a portable dissolved oxygen meter (Model: PDO-520, Taiwan) and a multi-parameter water quality meter (PHT-27, China), respectively. β-Carotene biosynthesis in GRSP and GRLE leaves was analyzed via HPLC-Shimadzu Prominence (Tokyo, Japan). This research was carried out for 4 consecutive seasons (winter, spring, autumn, and summer). The WT levels of the FWTP and DWCT components ranged from 12.12 ± 1.34–25.21 ± 0.95°C. The EC values of these 2 components ranged from 0.55 ± 0.05–0.65 ± 0.55 mS/cm. The WT and EC values were significantly (p < 0.05) different among the 4 seasons. Throughout the research period, the highest and lowest WT and EC levels were detected in the summer and winter periods, respectively. Furthermore, β-Carotene biosynthesis in the GRSP and GRLE leaves ranged from 3.63 ± 0.27–25.80 ± 6.67%. A significant (p 0.05) different was detected in the winter and spring. The highest level of β-Carotene biosynthesis was obtained in the summer. The results of the present study revealed that seasonal changes in WT and EC induced variations in β-Carotene biosynthesis in the studied vegetable materials. Hence, this work could be used to interpret better climate or growing conditions for sustainable food production. Aquaponic greenhouse β-Carotene biosynthesis Food production HPLC-Shimadzu Prominence Leafy green spinach Seasonal dynamics Figures Figure 1 Figure 2 Figure 3 Introduction One of the major environmental factors influencing secondary metabolite metabolism in plants is temperature fluctuations [ 1 , 2 ]. A warmer or colder temperature below or above the optimum range can reduce the photosynthetic rate of plants [ 3 , 4 ]. This in turn decreases the metabolite precursor pool for the biosynthesis of secondary metabolites such as carotenoid. Stress due to heat can cause chloroplasts to swell, inhibiting photosynthesis and thus plastoglobulin formation [ 5 ]. The amount of carotenoid biosynthesized in plants is species and tissue dependent in response to ambient temperature. Ambient temperatures above the range of 12 to 32°C decrease the biosynthesis of lycopene and other carotenoids in plants [ 6 , 7 ]. Another report revealed that an ambient temperature of 35°C can downregulate carotenoid biosynthesis [ 8 ]. Nutrients play a vital role in chloroplast development and carotenoid biosynthesis in plants [ 9 , 10 ]. Thus, nutrients deficiency or excess nutrients can affect carotenoid level in plants [ 11 , 12 ]. Furthermore, insufficient amounts of some metal ions in the soil and/or water alter chloroplast development and carotenoid synthesis in plants [ 12 , 13 ]. For example, iron deficiency impairs chloroplast thylakoid membranes, causing chlorosis in plant leaves [ 14 ]. The utilization of the heme b cofactor in the mediation of redox regulation in zeta-carotene isomerization highlights the need for Fe 3+ in carotenoid biosynthesis [ 15 ]. In addition, nitrogen availability can promote chloroplast development and carotenogenesis in plants [ 16 ]. For instance, nitrogen availability increases β-Carotene accumulation in vegetable plants such as carrot [ 17 ], spinach [ 18 ], and brassica [ 19 ]. Nitrogen deficiency or starvation can breakdown the chloroplast thylakoid membranes and photosynthetic pigments, causing yellowing of the plant leaves [ 16 ]. Photosynthetic pigments such as carotenoid trap photons of solar radiation to initiate electron transport, which converts light energy into chemical energy in photosynthetic plant leaves [ 20 , 21 ]. Carotenoid is 40-carbon lipophilic dietary nutrient that is vital for good visual acuity and reactive oxygen species detoxification [ 22 , 23 ]. β-Carotene is a carotenoid and the main precursor of vitamin A synthesis in humans [ 24 ]. Additionally, β-carotene is an essential metabolite of high demand in market as a natural coloring agent in the food and cosmetic industries [ 24 ]. The biosynthesis of β-Carotene in plants could be increased under greenhouse conditions [ 24 ]. Greenhouse structures can protect plants from the adverse effects of environmental factors such as wind, rain, pests, and insects [ 24 ]. Spinach ( Spinacia oleracea) is native to central and southwestern Asia and grows well in aquaponic greenhouse [ 25 – 27 ]. This green leafy vegetable requires high moisture, making it perfect in the system. It is edible and belongs to a genus and family of Amaranthus and Amaranthaceae , respectively [ 25 – 27 ]. Spinach grows to a height of 30 cm with variable leaf shapes that range from alternate, simple, ovate, and triangular [ 28 ]. It can survive best within the temperature range of 4.4–15°C and pH range of 6.4–6.8 [ 28 ]. There are 3 main types of spinach, namely, savoy, semisavoy, and smooth leaf [ 29 ]. Lettuce ( Lactuca sativa L.) was originally farmed by ancient Egyptians, belongs to the Asteraceae family, and is popularly used as a salad [ 30 – 32 ]. It is a widely cultivated and popularly consumed leafy plant globally, with China being the largest producer [ 33 ]. Lettuce grows faster in aquaponic greenhouses than in the soil [ 34 , 35 ]. Lettuce is among the first leafy vegetables cultivated commercially in hydroponic systems [ 34 ]. The faster growth cycle promotes the harvest of this vegetable within 4–5 weeks and thus allows quick profit and nutrient turnover [ 36 ]. There are numerous types of lettuce. However, based on leaf shape, texture, size, stem type, and head formation, there are 6 kinds of lettuce; crisp-head, butter-head, romaine, cutting stalk, asparagus, and Latin lettuce [ 33 ]. An aquaponic greenhouse is a sustainable farming practice for the production of fish and vegetable plants. It could provide a solution to the major problems associated with food production to feed the growing world population [ 37 , 38 ]. Owing to their close proximity of planting, aquaponic greenhouses enable the production of more plants per square foot than traditional agricultural methods, which require large tracts of land [ 39 ]. Additionally, plant roots absorb the required nutrients without competition with nonindigenous plants such as weeds, in contrast with conventional practices that require fertilizer application [ 40 , 41 ]. Furthermore, the aquaponic is usually set up inside a greenhouse to limit the adverse effects of biotic and abiotic factors, which increases the rapid growth rate, yield, and nutritional composition [ 42 , 43 ]. Edible plants in aquaponic greenhouses are classified into fruits (tomato, eggplant, pepper, and chili), leafy plants (lettuce, mint, and spinach), flowers (broccoli), bulbs (garlic and onion), and roots (carrot) [ 44 ]. These edible plants contain valuable metabolites that can benefit human health and nutrition [ 45 , 46 ]. Some of these metabolites include tocopherols, carotenoids, saponins, alkaloids, tannins, polyphenolics, and flavonoids [ 47 , 48 ]. Reports concerning the influence of seasonal variations in nutrient availability and temperature on β-carotene biosynthesis in plants grown in aquaponic greenhouses are lacking. However, Dzomeku et al. [ 49 ] reported that climate change increased the carotenoid (provitamin A) levels of some selected plantain cultivars. Additionally, Ivanova et al. [ 50 ] reported a study on the impacts of seasonal dynamics on the chlorophyll and carotenoid contents in steppe and forest plant leaves. According to another report, changes in climate determine the productivity and constituents of plants [ 51 ]. Therefore, the present study aimed to explore the effects of seasonal changes in electrical conductivity and water temperature on β-carotene biosynthesis in green spinach (Silver-beet) and green lettuce (Locarno) leaves from an aquaponic greenhouse. Materials and methods Aquaponic greenhouse site and set –up The research study was carried out in an aquaponic greenhouse located in the town of Makhanda (Grahams town), Eastern Cape, South Africa. It was set up as a coupled commercial greenhouse exposed to only ambient sunlight. The greenhouse consists of fish tanks (4 × 1,500 L), sump tanks (1 × 1,500 L and 1 × 500 L), flood-and-drain gravel stone media beds (20 × 400 L), and deep-water culture tanks (24 × 900 L). The fish, deep-water culture, and sump tanks have associated submersible pumps (SOBO ® , WP-7000, 105 W, 5000 L H -1 ). The system components were connected with PVC pipes to form a closed loop. Water sample collection Each water sample from the fish water tap (FWTP) and deep-water culture tank (DWCT) was collected into a clean 50 mL screw cap Falcon tube, placed on ice, and transported immediately to the laboratory for electrical conductivity (EC) determination. The water temperature (WT) assessment was carried out directly from each of the FWTP and DWCT components in the aquaponic greenhouse. The EC and WT analyses of the winter were conducted from the 29 th of June, 2020, to the 31 st of August, 2020. The spring assessment started on the 3 rd of September, 2020, and continued until the 30 th of November, 2020. In the summer, the determination commenced on the 3 rd of December, 2020, to the 1 st of March, 2021. Finally, the autumn evaluation initiated on the 4 th of March, 2021, and ended on the 27 th of May, 2021. The water samples were collected and analyzed twice weekly on Mondays and Thursdays throughout the study period. Plant sample collection Green spinach (GRSP) leaves of the Silver-beet cultivar were collected from a gravel stone media bed (GSMB). The green lettuce (GRLE) leaves of the Locarno cultivar were acquired from a polystyrene sheet in the deep-water culture tank (DWCT). The fish water tap (FWTP) and deep-water culture tank (DWCT) provide nutrient water for the GRSP and GRLE plants. Figure 1 shows the study vegetable plants. The plant materials were collected on the 21 st of August, 2020, for the winter. On the 24 th of November, 2020 for the spring. On the 1 st of March, 2021, for the summer. Finally, on the 30 th of May, 2021, for the autumn. Each sample was placed in a separate clean plastic bag and transported to the laboratory. On reaching the Laboratory, each plant material was then rinsed separately with Milli-Q water to remove contaminants and air-dried in an oven at 30 ° C. Lastly, each air-dried sample was ground into powder and stored in screwed-cap Falcon tubes. The Falcon tubes were covered with aluminum foil to prevent sensitive compounds from light-induced degradation. Reagents and apparatus The reagents and apparatus used were HPLC-grade β-carotene (Sigma-Aldrich, St. Louis, USA), HPLC-grade tetrahydrofuran (Merck, EMD Millipore Corporation, Germany), a Minisart syringe filter (0.22 µm) (Goppingen, Germany, LOT 00807103), Milli-Q water (EMD-Millipore machine, Switzerland), and HPLC amber vials. The equipment used were HPLC-Shimadzu-UFLC Prominence system (Shimadzu Corporation, Kyoto, Japan), Luna ® , 5 µm C18 (2) 100A column (150 × 4.6 mm) (Phenomenex, USA), a portable dissolved oxygen meter (Model: PDO-520, Taiwan), a multi-parameter water quality meter (PHT-27, China), an analytical weighing balance (RADWAG, 220 g × 0.1 mg, Model, AS/220/C/2, Poland), a BÜchi heating water bath (B-491, Switzerland), and a BÜchi rotary evaporator (R-210, Switzerland). All the reagents used in this study were of analytical grade. Standard preparation The stock solution of β-carotene (HPLC-grade) was prepared as reported by Gleize et al. [52] and Yokoto and Oshio [53] with a modification in concentration value. A 2.0 mg/mL stock solution was prepared by dissolving 10 mg of β-carotene in 5.0 mL of tetrahydrofuran (HPLC-grade). A working solution of β-carotene (1,000 µg/mL) was generated from its stock. Various concentrations of 2.5, 5, 10, 15, 40, 100, 200, 400, 500, and 1,000 µg/mL were prepared from the working solution by further dilution with tetrahydrofuran. All working solutions were filtered through a 0.22 µm acro-disc syringe filter prior to injection into the HPLC-machine. Sample extraction Each dried sample (5.0 g) of the green spinach and green lettuce was placed in a separate Falcon tube with addition of 2 mL of ascorbic acid (0.1%) to prevent oxidation. Methanol/dichloromethane (dilution solution) (30 mL) at a ratio of 2:1 v/v was added, and the mixture was vortexed well for 15 min. Each mixture was centrifuged at 4,000 rpm for 20 min. The supernatant of each mixture was then filtered through Whatman filter paper (11 µm pore size) and evaporated to dryness with a rotary evaporator under reduced pressure at 25 ° C. Each evaporated sample residue (2.0 mg) was suspended in 1.0 mL of the dilution solution and filtered through a 0.22 µm Minisart syringe filter before injection into the HPLC system for chromatography. The remaining residues were preserved at -20 ° C. Sample extraction was performed at room temperature (25±5 ° C) in the dark to minimize possible light-induced isomerization. Analytical methods Water temperature and electrical conductivity assessment The water temperature (WT) was determined via a portable dissolved oxygen meter, whereas the water electrical conductivity (EC) was measured via a multi-parameter water quality meter. Each parameter (WT and EC) was determined twice weekly (Mondays and Thursdays) for the entire 4 consecutive seasons study. β-carotene analysis Each leaf sample extract was injected in triplicate into the UV-HPLC-Shimadzu-UFLC Prominence system with LC-20AD connecter, LC-2AB pump (20 MPa), SIL-2A auto sampler, and SPDA-M20A diode array detector. The diode array detector (DAD) wavelength was set between 190 and 800 nm. The "LC Lab Solution" software was used for HPLC data acquisition and analysis. Chromatographic separation was performed with a Luna ® , 5 µm C18 (2) 100A column (150 × 4.6 mm). The mobile phase delivery was isocratic and consisted of tetrahydrofuran/water at a ratio of 97:3, v/v. The flow rate was 1.0 mL/min. The column was maintained at room temperature (25±5 ° C). The sample injection volume was 10 µL, and the mixture was run for 10 min. Ultraviolet-visible (UV-vis) absorbance was detected at a wavelength of 450 nm. Statistical analysis The study data were statistically analyzed with Microsoft Excel 365 ® (Microsoft Corporation, New York, USA) via repeated-measures analysis of variance (RM ANOVA). A significance level (5%) was utilized. As the RM ANOVA indicated a significant difference among the 4 comparative seasons, a post hoc test (unpaired Student's t-test) was performed to determine where a significant difference existed. Results The water temperature (WT) and electrical conductivity (EC) levels of the fish water tap (FWTP) and deep-water culture tank (DWCT) significantly (p < 0.05) differed among the 4 seasons (Table 1). The highest WT and EC values were detected in the summer, whereas the lowest levels were detected in the winter. The FWTP and DWCT components revealed similar trends of the WT and EC levels (Table 1). Table 1 Water temperature (WT) and electrical conductivity (EC) levels of the fish water tap (FWTP) and deep-water culture tank (DWCT) for the 4 seasons Water Quality Parameters Experimental Components Winter (June 2020 to August 2020) (n = 22) Spring (September 2020 to November 2020) (n = 24) Summer (December 2020 to March 2021) (n = 24) Autumn (March 2021 to May 2021) (n =24) WT ( ° C) FWTP 12.20±1.42 a 18.05±2.44 b 25.21±0.95 c 19.74±1.91 d DWCT 12.12±1.34 a 18.10±2.95 b 24.93±0.91 c 19.97±3.07 d EC (mS/cm) FWTP 0.56±0.05 a 0.59±0.04 b 0.64±0.04 c 0.62 c ±0.05 d DWCT 0.55±0.05 a 0. 60±0.04 b 0.65±0.05 c 0.61 c ±0.05 d Each parameter was analyzed twice weekly (Mondays and Thursdays) for the entire research period. The results are presented as the means ± SDs. Values with different superscript letters between seasons are significantly (p < 0.05) different. n signifies the number of times the water sample was collected per component per season. Figure 2 depicts the seasonal changes in the water temperature (WT) and electrical conductivity (EC) throughout the 4 seasons (94 days). The highest and lowest WT were obtained in summer and winter, respectively. Similarly, the maximum and minimum EC levels were recorded in the summer and winter, respectively. β-Carotene biosynthesis in green spinach (GRSP) leaves was not significantly (p > 0.05) different between winter (10.57±0.21%) and spring (9.36±3.37%). Similarly, the percentage of β-Carotene biosynthesis in green lettuce (GRLE) leaves was not significantly (p > 0.05) different between winter (4.13±4.55%) and spring (3.63±287%) (Figure 2). However, β-carotene bioaccumulation in the GRSP leaves was significantly (p < 0.05) different in the summer (25.80±6.67%) compared with autumn (17.19±2.08%). Likewise, β-Carotene biosynthesis in GRLE leaves was significantly (p < 0.05) different in the summer (15.36±5.95%) than in the autumn (10.11±5.06%) (Figure 2). The GRSP leaves presented the highest β-carotene biosynthesis in the summer. In contrast, GRLE leaves revealed the lowest β-carotene bioaccumulation in the spring (Figure 2). Discussion Aquaponic greenhouse technology is an important tool for improving the quantity and quality of vegetable food production. The dark green color of leafy spinach and lettuce indicates high levels of health-promoting carotenoids and chlorophylls [ 54 ]. β-Carotene is an active form of carotenoid referred to as provitamin A [ 55 , 56 ]. Many epidemiological studies have shown a strong relationship between β-carotene intake and a decreased risk of carcinogenesis, cardiovascular disease, neuronal damage, inflammation, and macular degeneration [ 57 , 58 ]. An adult normal blood level of β-carotene was reported to be approximately 9.0 µg/mL [ 59 , 60 ]. This study investigated the effects of seasonal variations in water temperature and electrical conductivity on β-carotene biosynthesis in green spinach (GRSP) and green lettuce (GRLE) leaves from an aquaponic greenhouse. Most plants require an optimal water temperature between 21 and 24°C to thrive and grow properly [ 61 ]. However, some local varieties can survive well outside the above range [ 61 ]. However, a water temperature below the optimal value can affect the availability of nutrients to plants [ 62 ]. Electrical conductivity (EC) is a measure of the total amount of dissolved ions or nutrients in water [ 63 , 64 ]. Dissolved ions such as nitrate, phosphate, potassium, zinc, and chloride can increase the electrical conductivity of water, which in turn accounts for the nutrients available to plants [ 65 ]. The recommended level of EC in aquaponic ranged from 0.3–0. 6 mS/cm [ 36 ]. The ability of microbes in aquaponic systems to metabolize and convert organic or inorganic compounds into plant nutrients is enhanced if the water temperature is optimal (25–30°C) [ 61 ]. In this study, the water temperature in the summer (± 25°C) was determined to be optimal. Thus, the observed optimal values of EC in this period (summer) could be due to increased microbial decomposition of organic matter (fish faces and feed remains) and nitrification processes. The presence of β-carotene in spinach and lettuce leaves was reported by Ahmad et al. [ 66 ], Isma’il and Fun [ 67 ], and Ju et al. [ 68 ], as detected in the present study. In the summer, the greater amounts of β-carotene in GRSP and GRLE leaves could be linked to their increased biosynthesis, which was associated with optimal levels in the water temperature (± 25°C) and electrical conductivity (± 0.63 mS/cm) during the season. Interestingly, the findings of this study are in line with those of De Azevedo-Meleiro and Rodriguez-Amaya [ 69 ]. They reported that the carotenoid contents in New Zealand and endive spinach were higher in the summer. Similarly, Shen et al. [ 70 ] reported that increased UV-radiation increases carotenoid bioaccumulation in tobacco leaves. In contrast, Dumaas et al. [ 6 ] and Hernandez et al. [ 7 ] reported that exposure of tomatoes to temperatures above 12–32°C decreases lycopene and carotenoid biosynthesis. Similarly, Tran and Raymundo [ 8 ] reported that a temperature of 35°C decreases carotenoid biosynthesis in bitter melon. Hence, increases in the water temperature and electrical conductivity because of seasonal changes have induced increases in β-carotene biosynthesis in the 2 leafy materials studied. Conclusion β-Carotene accumulates in relatively high amounts in leaves of the studied plant species during the summer (warmest season). Thus, β-carotene can provide an additional adaptive advantage of photo-oxidative stress tolerance in higher plants. As a food-based strategy, the studied plant materials could be good source of a sustainable vitamin A in developing countries. However, the bioavailability, conversion, and absorption of β-carotene in the body could be the challenge. Further studies are needed to better understand the biosynthesis and functions of this compound and other form of carotenoids in studied leafy plants and related species. Abbreviations DWCT Deep-water culture tank EC Electrical conductivity FWTP Fish water tap GRLE Green lettuce GRSP Green spinach HPLC High-performance liquid chromatography WT Water temperature Declarations Acknowledgments This study was supported by the Department of Biochemistry and Microbiology, Faculty of Science, Rhodes University, South Africa. Furthermore, I am grateful to the aquaponic greenhouse proprietor for keeping the system running throughout the study period. Author contributions The author carried out the conceptualization, formal analysis, investigations, data validation and curation, writing the original draft, reviewing, and editing. Availability of data and materials All the data obtained and or analyzed during the course of the study are included in this article. Funding Not applicable Ethics approval and consent to participate Not applicable. Publication consent Not applicable. Competing interests Author declare no competing interests. References Quint M, Delker C, Franklin KA, Wigge PA, Halliday KJ, van Zanten M. Molecular and genetic control of plant thermos-morphogenesis. Nat Plants. 2016;2:15190. https://doi.org/10.1038/nplants.2015.190. Delker C, Sonntag L, James GV, Janitza P, Ibanez C, Ziermann H, Peterson T, Denk K, Mull S, Ziegler J, Davis SJ, Schneeberger K, Quint M. The DET1-COP1-HY5 pathway constitutes a multipurpose signaling module regulating plant photo-morphogenesis and thermo-morphogenesis. 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Sace CF, Fitzsimmons KM, Vegetable production in a recirculating aquaponic system using Nile tilapia ( Oreochromis niloticus ) with and without freshwater prawn ( Macrobrachium rosenbergii ). Acad J Agric Res. 2013;1(12):236–250. Rakocy JE, Michael P, Masser J, Losordo T. Recirculating aquaculture tank production systems: Aquaponics – integrating fish and plant culture. Southern Regional. Stoneville, Mississippi; 2006. Castro, RS, Azevedo CMSB, Bezerra-Neto, F. Increasing cherry tomato yield using fish effluent as irrigation water in Northeast Brazil. Scientia Hort. 2006;110:44–50. Diver S. Aquaponics—integration of hydroponics with aquaculture. National Centre for Appropriate Technology (NCAT), Butte, ATTRA. 2006; p. 1–28. Rakocy JE, Hargreaves JA, Bailey DS. Nutrient accumulation in a recirculating aquaculture system integrated with hydroponic vegetable production. Wang JK, editor. Techniques of modern aquaculture. American Society of Agricultural Engineers. Missouri: USA; 1993. p. 148–158. Savidov N, Hutchings ER. Fish and plant production in a recirculating aquaponic system: A new approach to sustainable agriculture in Canada. ISHS. Acta Hort. 2005;742:209–224. Savidov NA. Annual report of greenhouse crops program for 2003/2004. CDC South Canada. 2004. p. 470. Blidariu F, Grozea A, Increasing the economic efficiency and sustainability of indoor fish farming by means of aquaponics – Review. Bull Ani Sci Biotech. 2011;2: 44. Brook R. Home aquaponics system: Top ten benefits of having aquaponics at home. (2017). http:www.homeaquaponicssystem.com/basics/top-10-benefits-of-having aquaponics-at-home (Accessed 12 April 2022). Ukom AN, Obi JA. Comparative evaluation of the nutrient composition and phytochemical content of selected vegetables consumed in Nigeria. Int Letters Nat Sci. 2018;71:43–50. Braglia R, Costa P, Di Marco G, D'Agostino A, Redi EL, Scuderi F, Gismondi A, Canini A. Phytochemicals and quality level of food plants grown in an aquaponics system. Sci Food Agri. 2021;2021:1–7. Karasawa MMG, Mohan C. Fruits as prospective reserves of bioactive compounds: A review. Nat Products Biopros. 2018;8:335–346. Kris-Etherton PM, Hecker KD, Bonanome A, Coval SM, Binkoski AE, Hilpert KF. Bioactive compounds in foods: their role in the prevention of cardiovascular diseases and cancer. Am J Med. 2002;113(9B):71S–88S. WHO. Chronic disease: key risk factors include high cholesterol, high blood pressure, low fruit, and vegetable intake. World Health Organization. Geneva: Switzerland; 2003. Dzomeku MB, Wald JP, Wünsche JN, Nohr D, Biesalski, HK. Climate change enhanced carotenoid Pro-Vitamin A levels of selected plantain cultivars. Plants. 2020;9:541. doi:10.3390/plants9040541. Ivanova LA, Ronzhinaa DA, Yudinaa PK, Zolotarevac NV, Kalashnikovaa IV, Ivanovaa LA. Seasonal dynamics of the chlorophyll and carotenoid content in the leaves of Steppe and forest plants on species and community level. Russ J Plant Physiol. 2020;(67)3:453–462. Herrera RS., Verdecia DM, Ramirez JL, Garcia M, Cruz AM. Secondary metabolites of Leucaena leucocephala . Their relationship with some climate elements, different expression of digestibility and primary metabolites. Cuban J Agric Sci . 2017;5(1):107–116. Gleize B, Steib M, Andre M, Reboul E. Simple and fast HPLC method for simultaneous determination of retinol, tocopherols, coenzyme Q10 and carotenoids in complex samples. Food Chem. 2012;134:2560–2564. Yokoto S, Oshio S. A simple and robust quantitative analysis of retinol and retinyl palmitate using a liquid chromatographic isocratic method. J Food Drug Anal. 2017;26:504–511. Petrea SM, Cristea V, Dediu L, Contoman M, Lupoae P, Mocanu MC, Coada MT. Vegetable production in an integrated aquaponic system with rainbow trout and spinach. Bulletin of University of Agricultural Science and Veterinary Medicine. Ani Sci Biotech. 2013;70(1):45–54. Ishida BK, Bartley GE. Carotenoids: chemistry, source, and physiology. In Allen L, Prentice A. 2nd editors, Encyclopedia of human nutrition United Kingdom: Elsevier Limited.; 2005. p. 330–339. Scott KJ, Rodriquez-Amaya G. Pro-vitamin A carotenoid conversion factors: Retinol equivates-fact of fiction? Food Chem. 2000;69:125–127. Cantuti-Castelvetri I, Shukitt-Hale B, Joseph JA. Neurobehavioral aspects of antioxidant aging. Int J Dev Neurosci. 2000;18(4–5):367–381. Yamaguchi M, Uchiyama S. Effect of carotenoids on calcium content and alkaline phosphatase activity in rat femoral tissues in vitro: the unique anabolic effect of beta-cryptoxanthin. Bio Pharm Bull . 2003;26(8):1188–1191. Beers MH. Vitamin deficiency, dependency, and toxicity. Merck Manual of diagnosis and therapy. 18th ed. Merck and Co: Whitehouse Station; 2006. USDA (United States Drugs and Administration). National Nutrient Database for Standard Reference Release 28: Washington; 2019. Sallenave R. Important water quality parameters in aquaponics systems. Extension aquatic ecology specialist, department of extension animal sciences and natural resources, New Mexico State University. Circular. 2016;680:1–8. Helene V, Ivar R. Effect of temperature on feeding and digestive processes in fish. Temperature, 2020;7(4):307–320. https://doi.org/10.1080/23328940.2020.1765950. Manju M, Karthik V, Hariharan S, Sreekar B. Real time monitoring of the environmental parameters of an aquaponic system based on Internet of Things. In: Third International Conference on Science Technology Engineering and Management. 2017;943–948. Nagayo AM, Mendoza C, Vega E, Izki RKS, Jamisola RS. An automated solar-powered aquaponics system toward agricultural sustainability in the Sultanate of Oman. In: IEEE International Conference on Smart Grid and Smart Cities. 2017;42–49. Brinkop WS, Piedrahita RH, Water quality modeling for aquaculture water reuse systems. Paper presented at successes and failures in commercial recirculating aquaculture conference: Roanoke; USA. 1996;2:521–530. Ahmad MN, Saleemullah M, Shah HU. Determination of β-Carotene content in fresh vegetables using high-performance liquid chromatography. Sarhad J Agric. 2007;23(3):766-770. Ismail A, Fun CS. Determination of vitamin C, β-Carotene, and riboflavin contents of five green vegetables organically and conventionally grown. Malays J Nutr. 2003;9(1):31–39. Ju JH, Cho SY, Song HY, Ju S, Yoon YH, Yeum KJ. Growth and carotenoid contents of intercropped vegetables in building-integrated urban agriculture. J Food Quality. 2021;9:ArticleID1159567. De Azevedo-Meleiro CH, SRodriguez-Amaya D. Carotenoids of endive and New Zealand spinach as affected by maturity, season and minimal processing. J. Food Compos. Anal. 2005;18:845–855. Shen J, Jiang CQ, Yan YF, Liu BR, Zu C. Effect of increased UV-B radiation on carotenoid accumulation and total antioxidant capacity in tobacco ( Nicotiana tabacum L.) leaves. Genet Mol. Res. 2017;16:1–11. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted 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-5898385","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":408566780,"identity":"a95434bd-d49f-4f2e-a66e-e7070fc696db","order_by":0,"name":"Labaran Ibrahim","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABFUlEQVRIiWNgGAWjYBACPgYeMM1jwMDAxpDAYMPDD+ImFODWwoamJU1OsgGkxYCwFgawFgaGw8YGB6BcnFrYzx78XFFzR8Zc+vCzBw9z0hI3n1+d+OGBAYM8v9gB7Fp48pIlzxx7xmPZl2ZukLjNJnHbjbebJYAOM5w5OwGHw3IMJBvYDvMYnGEwk0jclgbUcnYDSEuCwW0cWvjfGP9s+AfSwv4NqOVw4uYZZzf/wKtFIsdMsrENpIUHZAvQ+/y92/DbIvEuzbKx7zCPZQ9PGchhchI3eLdZJBhI4PQLP3/u4ZsN3w7bm/Owb5P8uQ0Ylf1nN9/8UWEjzy+NXQsWIAFWKUGscrDFB0hRPQpGwSgYBSMAAADCpV7XCjGcyQAAAABJRU5ErkJggg==","orcid":"","institution":"Federal University Dutse","correspondingAuthor":true,"prefix":"","firstName":"Labaran","middleName":"","lastName":"Ibrahim","suffix":""}],"badges":[],"createdAt":"2025-01-24 22:08:07","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5898385/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5898385/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":75145127,"identity":"989cfda6-c97e-45b4-a0e3-09254274952e","added_by":"auto","created_at":"2025-01-31 06:29:26","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":957703,"visible":true,"origin":"","legend":"\u003cp\u003eStudy plants: (a) Green spinach (GRSP) of the Silver-Beet cultivar in a wicking bucket to support the growing roots and (b) green lettuce (GRLE) of the Locarno cultivar on the polystyrene raft. The GRSP was grown on a gravel stone media bed. The GRLE was cultivated on polystyrene raft in deep-water culture tank.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-5898385/v1/5da3e18878bc8797d439f48f.png"},{"id":75145129,"identity":"02652eb3-87dc-4dd1-943c-bdb98d4ad3bb","added_by":"auto","created_at":"2025-01-31 06:29:26","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":55462,"visible":true,"origin":"","legend":"\u003cp\u003eSeasonal variation in the (a) water temperature (WT) and (a) electrical conductivity (EC) values for the entire study period (94 days). The highest (29.4 \u003csup\u003e°\u003c/sup\u003eC) and lowest (9.4 \u003csup\u003e°\u003c/sup\u003eC) WT levels were detected in the summer and winter, respectively. Similarly, the maximum (0.86 mS/cm) and minimum (0.49 mS/cm) EC values were obtained in the summer and winter, respectively. DWCT represents the deep-water culture tank, and FWTP represents the fish water tap.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-5898385/v1/bd7b232637a15ffa85beab54.png"},{"id":75145365,"identity":"cf18b081-7967-48a1-bde2-1b2c245a052e","added_by":"auto","created_at":"2025-01-31 06:37:26","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":13133,"visible":true,"origin":"","legend":"\u003cp\u003eSeasonal differences in β-carotene biosynthesis amongthe 4 seasons of the 2 leafy materials. GRSP denotes green spinach, GRLE stands for green lettuce, dw indicates dry weight, ns represents no significant (p \u0026gt; 0.05) difference, and * reveals significant (p \u0026lt; 0.05) variation.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-5898385/v1/6fe1ed0a61e53702f0201ac1.png"},{"id":80779180,"identity":"9c89fc3e-a083-41da-9b05-36e7dd63acd3","added_by":"auto","created_at":"2025-04-17 04:16:43","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1672211,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5898385/v1/486d7bd4-7ce8-466b-8eda-dac11c399f1e.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effect of Seasonal Dynamics in Water Temperature and Electrical Conductivity on β- Carotene Biosynthesis in Green Spinach (Silver-beet) and Lettuce (Locarno) Leaves from Aquaponic Greenhouse","fulltext":[{"header":"Introduction","content":"\u003cp\u003eOne of the major environmental factors influencing secondary metabolite metabolism in plants is temperature fluctuations [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. A warmer or colder temperature below or above the optimum range can reduce the photosynthetic rate of plants [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. This in turn decreases the metabolite precursor pool for the biosynthesis of secondary metabolites such as carotenoid. Stress due to heat can cause chloroplasts to swell, inhibiting photosynthesis and thus plastoglobulin formation [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. The amount of carotenoid biosynthesized in plants is species and tissue dependent in response to ambient temperature. Ambient temperatures above the range of 12 to 32\u0026deg;C decrease the biosynthesis of lycopene and other carotenoids in plants [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Another report revealed that an ambient temperature of 35\u0026deg;C can downregulate carotenoid biosynthesis [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eNutrients play a vital role in chloroplast development and carotenoid biosynthesis in plants [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Thus, nutrients deficiency or excess nutrients can affect carotenoid level in plants [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Furthermore, insufficient amounts of some metal ions in the soil and/or water alter chloroplast development and carotenoid synthesis in plants [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. For example, iron deficiency impairs chloroplast thylakoid membranes, causing chlorosis in plant leaves [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. The utilization of the heme b cofactor in the mediation of redox regulation in zeta-carotene isomerization highlights the need for Fe\u003csup\u003e3+\u003c/sup\u003e in carotenoid biosynthesis [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. In addition, nitrogen availability can promote chloroplast development and carotenogenesis in plants [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. For instance, nitrogen availability increases β-Carotene accumulation in vegetable plants such as carrot [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], spinach [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e], and brassica [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Nitrogen deficiency or starvation can breakdown the chloroplast thylakoid membranes and photosynthetic pigments, causing yellowing of the plant leaves [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePhotosynthetic pigments such as carotenoid trap photons of solar radiation to initiate electron transport, which converts light energy into chemical energy in photosynthetic plant leaves [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Carotenoid is 40-carbon lipophilic dietary nutrient that is vital for good visual acuity and reactive oxygen species detoxification [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. β-Carotene is a carotenoid and the main precursor of vitamin A synthesis in humans [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Additionally, β-carotene is an essential metabolite of high demand in market as a natural coloring agent in the food and cosmetic industries [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. The biosynthesis of β-Carotene in plants could be increased under greenhouse conditions [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Greenhouse structures can protect plants from the adverse effects of environmental factors such as wind, rain, pests, and insects [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eSpinach (\u003cem\u003eSpinacia oleracea)\u003c/em\u003e is native to central and southwestern Asia and grows well in aquaponic greenhouse [\u003cspan additionalcitationids=\"CR26\" citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. This green leafy vegetable requires high moisture, making it perfect in the system. It is edible and belongs to a genus and family of \u003cem\u003eAmaranthus\u003c/em\u003e and \u003cem\u003eAmaranthaceae\u003c/em\u003e, respectively [\u003cspan additionalcitationids=\"CR26\" citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Spinach grows to a height of 30 cm with variable leaf shapes that range from alternate, simple, ovate, and triangular [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. It can survive best within the temperature range of 4.4\u0026ndash;15\u0026deg;C and pH range of 6.4\u0026ndash;6.8 [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. There are 3 main types of spinach, namely, savoy, semisavoy, and smooth leaf [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eLettuce (\u003cem\u003eLactuca sativa\u003c/em\u003e L.) was originally farmed by ancient Egyptians, belongs to the Asteraceae family, and is popularly used as a salad [\u003cspan additionalcitationids=\"CR31\" citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. It is a widely cultivated and popularly consumed leafy plant globally, with China being the largest producer [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. Lettuce grows faster in aquaponic greenhouses than in the soil [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Lettuce is among the first leafy vegetables cultivated commercially in hydroponic systems [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. The faster growth cycle promotes the harvest of this vegetable within 4\u0026ndash;5 weeks and thus allows quick profit and nutrient turnover [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. There are numerous types of lettuce. However, based on leaf shape, texture, size, stem type, and head formation, there are 6 kinds of lettuce; crisp-head, butter-head, romaine, cutting stalk, asparagus, and Latin lettuce [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAn aquaponic greenhouse is a sustainable farming practice for the production of fish and vegetable plants. It could provide a solution to the major problems associated with food production to feed the growing world population [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. Owing to their close proximity of planting, aquaponic greenhouses enable the production of more plants per square foot than traditional agricultural methods, which require large tracts of land [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. Additionally, plant roots absorb the required nutrients without competition with nonindigenous plants such as weeds, in contrast with conventional practices that require fertilizer application [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. Furthermore, the aquaponic is usually set up inside a greenhouse to limit the adverse effects of biotic and abiotic factors, which increases the rapid growth rate, yield, and nutritional composition [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. Edible plants in aquaponic greenhouses are classified into fruits (tomato, eggplant, pepper, and chili), leafy plants (lettuce, mint, and spinach), flowers (broccoli), bulbs (garlic and onion), and roots (carrot) [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. These edible plants contain valuable metabolites that can benefit human health and nutrition [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. Some of these metabolites include tocopherols, carotenoids, saponins, alkaloids, tannins, polyphenolics, and flavonoids [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eReports concerning the influence of seasonal variations in nutrient availability and temperature on β-carotene biosynthesis in plants grown in aquaponic greenhouses are lacking. However, Dzomeku et al. [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e] reported that climate change increased the carotenoid (provitamin A) levels of some selected plantain cultivars. Additionally, Ivanova et al. [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e] reported a study on the impacts of seasonal dynamics on the chlorophyll and carotenoid contents in steppe and forest plant leaves. According to another report, changes in climate determine the productivity and constituents of plants [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e]. Therefore, the present study aimed to explore the effects of seasonal changes in electrical conductivity and water temperature on β-carotene biosynthesis in green spinach (Silver-beet) and green lettuce (Locarno) leaves from an aquaponic greenhouse.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cp\u003e\u003cstrong\u003eAquaponic\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;greenhouse\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003esite and set\u003c/strong\u003e\u003cstrong\u003e\u0026ndash;up\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe research study was carried out in an\u0026nbsp;aquaponic greenhouse located in the town of Makhanda (Grahams town), Eastern Cape, South Africa. It was set up as a coupled commercial greenhouse exposed to only ambient sunlight. The greenhouse consists of fish tanks (4 \u0026times; 1,500 L), sump tanks (1 \u0026times; 1,500 L and 1 \u0026times; 500 L), flood-and-drain gravel stone media beds (20 \u0026times; 400 L), and deep-water culture tanks (24 \u0026times; 900 L). The fish, deep-water culture, and sump tanks have associated submersible pumps (SOBO\u003csup\u003e\u0026reg;\u003c/sup\u003e, WP-7000, 105 W, 5000 L H\u003csup\u003e-1\u003c/sup\u003e). The system components were connected with PVC pipes to form a closed loop.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eWater\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003esample\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;collection\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEach water sample from the fish water tap (FWTP) and deep-water culture tank (DWCT) was collected into a clean 50 mL screw cap Falcon tube, placed on ice, and transported immediately to the laboratory for electrical conductivity (EC) determination. The water temperature (WT) assessment was carried out directly from each of the FWTP and DWCT components in the aquaponic greenhouse. The EC and WT analyses of the winter were conducted from the 29\u003csup\u003eth\u003c/sup\u003e of June, 2020, to the 31\u003csup\u003est\u003c/sup\u003e of August, 2020. The spring assessment started on the 3\u003csup\u003erd\u003c/sup\u003e of September, 2020, and continued until the 30\u003csup\u003eth\u003c/sup\u003e of November, 2020. In the summer, the determination commenced on the 3\u003csup\u003erd\u003c/sup\u003e of December, 2020, to the 1\u003csup\u003est\u003c/sup\u003e of March, 2021. Finally, the autumn evaluation initiated on the 4\u003csup\u003eth\u003c/sup\u003e of March, 2021, and ended on the 27\u003csup\u003eth\u003c/sup\u003e of May, 2021. The water samples were collected and analyzed twice weekly on Mondays and Thursdays throughout the study period.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePlant\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003esample\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;collection\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eGreen spinach (GRSP) leaves of the Silver-beet cultivar were collected from\u0026nbsp;a\u0026nbsp;gravel stone media\u0026nbsp;bed (GSMB).\u0026nbsp;The\u0026nbsp;green lettuce (GRLE) leaves of\u0026nbsp;the\u0026nbsp;Locarno cultivar\u0026nbsp;were acquired from a polystyrene sheet\u0026nbsp;in\u0026nbsp;the\u0026nbsp;deep-water culture tank (DWCT).\u0026nbsp;The fish water tap (FWTP) and deep-water culture tank (DWCT) provide\u0026nbsp;nutrient\u0026nbsp;water for the GRSP and GRLE plants. Figure 1 shows\u0026nbsp;the study vegetable plants. The plant materials were collected\u0026nbsp;on the\u0026nbsp;21\u003csup\u003est\u0026nbsp;\u003c/sup\u003eof August,\u0026nbsp;2020,\u0026nbsp;for the winter.\u0026nbsp;On the 24\u003csup\u003eth\u0026nbsp;\u003c/sup\u003eof November,\u0026nbsp;2020 for the spring.\u0026nbsp;On the\u0026nbsp;1\u003csup\u003est\u0026nbsp;\u003c/sup\u003eof March,\u0026nbsp;2021,\u0026nbsp;for the summer. Finally, on the 30\u003csup\u003eth\u0026nbsp;\u003c/sup\u003eof May, 2021, for the autumn. Each sample was placed in a separate clean plastic bag and transported to the laboratory. On reaching the Laboratory, each plant material was then rinsed separately with Milli-Q water to remove contaminants and air-dried in an oven at 30 \u003csup\u003e\u0026deg;\u003c/sup\u003eC. Lastly, each air-dried sample was\u0026nbsp;ground\u0026nbsp;into powder and stored in screwed-cap\u0026nbsp;Falcon\u0026nbsp;tubes. The Falcon tubes were covered with aluminum foil to prevent sensitive compounds from light-induced degradation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eReagents and apparatus\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe reagents and apparatus used were HPLC-grade \u0026beta;-carotene (Sigma-Aldrich, St. Louis, USA), HPLC-grade tetrahydrofuran (Merck, EMD Millipore Corporation, Germany), a Minisart syringe filter (0.22 \u0026micro;m) (Goppingen, Germany, LOT 00807103), Milli-Q water (EMD-Millipore machine, Switzerland), and\u0026nbsp;HPLC amber vials. The equipment used were HPLC-Shimadzu-UFLC Prominence system (Shimadzu Corporation, Kyoto, Japan), Luna\u003csup\u003e\u0026reg;\u003c/sup\u003e, 5 \u0026micro;m C18 (2) 100A column (150 \u0026times; 4.6 mm) (Phenomenex, USA), a portable dissolved oxygen meter (Model: PDO-520, Taiwan), a multi-parameter water quality meter (PHT-27, China), an analytical weighing balance (RADWAG, 220 g \u0026times; 0.1 mg, Model, AS/220/C/2, Poland), a B\u0026Uuml;chi heating water bath (B-491, Switzerland), and a B\u0026Uuml;chi rotary evaporator (R-210, Switzerland). All the reagents used in this study were of analytical grade.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eStandard preparation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe stock solution of \u0026beta;-carotene (HPLC-grade) was prepared as reported by Gleize et al. [52] and Yokoto and Oshio [53] with a modification in concentration value. A 2.0 mg/mL stock solution was prepared by dissolving 10 mg of \u0026beta;-carotene in 5.0 mL of tetrahydrofuran (HPLC-grade). A working solution of \u0026beta;-carotene (1,000 \u0026micro;g/mL) was generated from its stock. Various concentrations of 2.5, 5, 10, 15, 40, 100, 200, 400, 500, and 1,000 \u0026micro;g/mL were prepared from the working solution by further dilution with tetrahydrofuran. All working solutions were filtered through a 0.22 \u0026micro;m acro-disc syringe filter prior to injection into the HPLC-machine.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSample\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;extraction\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEach dried sample (5.0 g) of the green spinach and green lettuce was placed in a separate Falcon tube with addition of 2 mL of ascorbic acid (0.1%) to prevent oxidation. Methanol/dichloromethane (dilution solution) (30 mL) at a ratio of 2:1 v/v was added, and the mixture was vortexed well for 15 min. Each mixture was centrifuged at 4,000 rpm for 20 min. The supernatant of each mixture was then filtered through Whatman filter paper (11 \u0026micro;m pore size) and evaporated to dryness with a rotary evaporator under reduced pressure at 25 \u003csup\u003e\u0026deg;\u003c/sup\u003eC. Each evaporated sample residue (2.0 mg) was suspended in 1.0 mL of the dilution solution and filtered through a 0.22 \u0026micro;m Minisart syringe filter before injection into the HPLC system for chromatography. The remaining residues were preserved at -20 \u003csup\u003e\u0026deg;\u003c/sup\u003eC. Sample extraction was performed at room temperature (25\u0026plusmn;5 \u003csup\u003e\u0026deg;\u003c/sup\u003eC) in the dark to minimize possible light-induced isomerization.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAnalytical methods\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eWater temperature and electrical conductivity assessment\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe water temperature (WT) was determined via a portable dissolved oxygen meter, whereas the water electrical conductivity (EC) was measured via a multi-parameter water quality meter. Each parameter (WT and EC) was determined twice weekly (Mondays and Thursdays) for the entire 4 consecutive seasons study.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026beta;-carotene analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEach leaf sample extract was injected in triplicate into the UV-HPLC-Shimadzu-UFLC Prominence system with\u0026nbsp;LC-20AD connecter, LC-2AB pump (20 MPa), SIL-2A auto sampler, and SPDA-M20A diode array detector. The diode array detector (DAD) wavelength was set between 190 and 800 nm. The \u0026quot;LC Lab Solution\u0026quot; software was used for HPLC data acquisition and analysis. Chromatographic separation was performed with a Luna\u003csup\u003e\u0026reg;\u003c/sup\u003e, 5 \u0026micro;m C18 (2) 100A column (150 \u0026times; 4.6 mm). The mobile phase delivery was isocratic and consisted of tetrahydrofuran/water at a ratio of 97:3, v/v. The flow rate was 1.0 mL/min. The column was maintained at room temperature (25\u0026plusmn;5 \u003csup\u003e\u0026deg;\u003c/sup\u003eC). The sample injection volume was 10 \u0026micro;L, and the mixture was run for 10 min. Ultraviolet-visible (UV-vis) absorbance was detected at a wavelength of 450 nm.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eStatistical analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study data were statistically analyzed with Microsoft Excel 365\u003csup\u003e\u0026reg;\u003c/sup\u003e (Microsoft Corporation, New York, USA) via repeated-measures analysis of variance (RM ANOVA). A significance level (5%) was utilized. As the RM ANOVA indicated a significant difference among the 4 comparative seasons, a \u003cem\u003epost\u003c/em\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003cem\u003ehoc\u0026nbsp;\u003c/em\u003etest (unpaired Student\u0026apos;s t-test) was performed to determine where a significant difference existed.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eThe water temperature (WT) and electrical conductivity (EC) levels of the fish water tap (FWTP) and deep-water culture tank (DWCT) significantly (p \u0026lt; 0.05) differed among the 4 seasons (Table 1). The highest WT and EC values were detected in the summer, whereas the lowest levels were detected in the winter. The FWTP and DWCT components revealed similar trends of the WT and EC levels (Table 1).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1\u0026nbsp;\u003c/strong\u003eWater temperature (WT) and electrical conductivity (EC) levels of the fish water tap (FWTP) and deep-water culture tank (DWCT) for the 4 seasons\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eWater Quality\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eParameters\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eExperimental Components\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eWinter (June 2020 to August 2020)\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(n = 22)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSpring (September 2020 to November 2020)\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(n = 24)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSummer (December 2020 to March 2021)\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(n = 24)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAutumn (March 2021 to May 2021)\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(n =24)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 95px;\"\u003e\n \u003cp\u003eWT (\u003csup\u003e\u0026deg;\u003c/sup\u003eC)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003eFWTP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e12.20\u0026plusmn;1.42\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e18.05\u0026plusmn;2.44\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e25.21\u0026plusmn;0.95\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e19.74\u0026plusmn;1.91\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003eDWCT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e12.12\u0026plusmn;1.34\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e18.10\u0026plusmn;2.95\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e24.93\u0026plusmn;0.91\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e19.97\u0026plusmn;3.07\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 95px;\"\u003e\n \u003cp\u003eEC (mS/cm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003eFWTP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e0.56\u0026plusmn;0.05\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e0.59\u0026plusmn;0.04\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e0.64\u0026plusmn;0.04\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e0.62\u003csup\u003ec\u003c/sup\u003e\u0026plusmn;0.05\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003eDWCT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e0.55\u0026plusmn;0.05\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e0. 60\u0026plusmn;0.04\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e0.65\u0026plusmn;0.05\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e0.61\u003csup\u003ec\u003c/sup\u003e\u0026plusmn;0.05\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eEach parameter was analyzed twice weekly (Mondays and Thursdays) for the entire research period. The results are presented as the means \u0026plusmn; SDs. Values with different superscript letters between seasons are significantly (p \u0026lt; 0.05) different. n signifies the number of times the water sample was collected per component per season.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFigure 2 depicts the seasonal changes in the water temperature (WT) and electrical conductivity (EC) throughout the 4 seasons (94 days). The highest and lowest WT were obtained in summer and winter, respectively. Similarly, the maximum and minimum EC levels were recorded in the summer and winter, respectively.\u003c/p\u003e\n\u003cp\u003e\u0026beta;-Carotene biosynthesis in green spinach (GRSP) leaves was not significantly (p \u0026gt; 0.05) different between winter (10.57\u0026plusmn;0.21%) and spring (9.36\u0026plusmn;3.37%). Similarly, the percentage of \u0026beta;-Carotene biosynthesis in green lettuce (GRLE) leaves was not significantly (p \u0026gt; 0.05) different between winter (4.13\u0026plusmn;4.55%) and spring (3.63\u0026plusmn;287%) (Figure 2). However, \u0026beta;-carotene bioaccumulation in the GRSP leaves was significantly (p \u0026lt; 0.05) different in the summer (25.80\u0026plusmn;6.67%) compared with autumn (17.19\u0026plusmn;2.08%). Likewise, \u0026beta;-Carotene biosynthesis in GRLE leaves was significantly (p \u0026lt; 0.05) different in the summer (15.36\u0026plusmn;5.95%) than in the autumn (10.11\u0026plusmn;5.06%) (Figure 2). The GRSP leaves presented the highest \u0026beta;-carotene biosynthesis in the summer. In contrast, GRLE leaves revealed the lowest \u0026beta;-carotene bioaccumulation in the spring (Figure 2).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eAquaponic greenhouse technology is an important tool for improving the quantity and quality of vegetable food production. The dark green color of leafy spinach and lettuce indicates high levels of health-promoting carotenoids and chlorophylls [\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e]. β-Carotene is an active form of carotenoid referred to as provitamin A [\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e, \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e]. Many epidemiological studies have shown a strong relationship between β-carotene intake and a decreased risk of carcinogenesis, cardiovascular disease, neuronal damage, inflammation, and macular degeneration [\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e, \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e]. An adult normal blood level of β-carotene was reported to be approximately 9.0 \u0026micro;g/mL [\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e, \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThis study investigated the effects of seasonal variations in water temperature and electrical conductivity on β-carotene biosynthesis in green spinach (GRSP) and green lettuce (GRLE) leaves from an aquaponic greenhouse. Most plants require an optimal water temperature between 21 and 24\u0026deg;C to thrive and grow properly [\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e]. However, some local varieties can survive well outside the above range [\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e]. However, a water temperature below the optimal value can affect the availability of nutrients to plants [\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e]. Electrical conductivity (EC) is a measure of the total amount of dissolved ions or nutrients in water [\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e, \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e]. Dissolved ions such as nitrate, phosphate, potassium, zinc, and chloride can increase the electrical conductivity of water, which in turn accounts for the nutrients available to plants [\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e]. The recommended level of EC in aquaponic ranged from 0.3\u0026ndash;0. 6 mS/cm [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. The ability of microbes in aquaponic systems to metabolize and convert organic or inorganic compounds into plant nutrients is enhanced if the water temperature is optimal (25\u0026ndash;30\u0026deg;C) [\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e]. In this study, the water temperature in the summer (\u0026plusmn;\u0026thinsp;25\u0026deg;C) was determined to be optimal. Thus, the observed optimal values of EC in this period (summer) could be due to increased microbial decomposition of organic matter (fish faces and feed remains) and nitrification processes.\u003c/p\u003e \u003cp\u003eThe presence of β-carotene in spinach and lettuce leaves was reported by Ahmad et al. [\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e], Isma\u0026rsquo;il and Fun [\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e], and Ju et al. [\u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e], as detected in the present study. In the summer, the greater amounts of β-carotene in GRSP and GRLE leaves could be linked to their increased biosynthesis, which was associated with optimal levels in the water temperature (\u0026plusmn;\u0026thinsp;25\u0026deg;C) and electrical conductivity (\u0026plusmn;\u0026thinsp;0.63 mS/cm) during the season. Interestingly, the findings of this study are in line with those of De Azevedo-Meleiro and Rodriguez-Amaya [\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e]. They reported that the carotenoid contents in New Zealand and endive spinach were higher in the summer. Similarly, Shen et al. [\u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e70\u003c/span\u003e] reported that increased UV-radiation increases carotenoid bioaccumulation in tobacco leaves. In contrast, Dumaas et al. [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e] and Hernandez et al. [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] reported that exposure of tomatoes to temperatures above 12\u0026ndash;32\u0026deg;C decreases lycopene and carotenoid biosynthesis. Similarly, Tran and Raymundo [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] reported that a temperature of 35\u0026deg;C decreases carotenoid biosynthesis in bitter melon. Hence, increases in the water temperature and electrical conductivity because of seasonal changes have induced increases in β-carotene biosynthesis in the 2 leafy materials studied.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eβ-Carotene accumulates in relatively high amounts in leaves of the studied plant species during the summer (warmest season). Thus, β-carotene can provide an additional adaptive advantage of photo-oxidative stress tolerance in higher plants. As a food-based strategy, the studied plant materials could be good source of a sustainable vitamin A in developing countries. However, the bioavailability, conversion, and absorption of β-carotene in the body could be the challenge. Further studies are needed to better understand the biosynthesis and functions of this compound and other form of carotenoids in studied leafy plants and related species.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eDWCT Deep-water culture tank\u003c/p\u003e\n\u003cp\u003eEC Electrical conductivity\u003c/p\u003e\n\u003cp\u003eFWTP Fish water tap\u003c/p\u003e\n\u003cp\u003eGRLE Green lettuce\u003c/p\u003e\n\u003cp\u003eGRSP Green spinach\u003c/p\u003e\n\u003cp\u003eHPLC High-performance liquid chromatography\u003c/p\u003e\n\u003cp\u003eWT Water temperature\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was supported by the Department of Biochemistry and Microbiology, Faculty of Science, Rhodes University, South Africa. Furthermore, I am grateful to the aquaponic greenhouse proprietor for keeping the system running throughout the study period.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003econtributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe author carried out the conceptualization, formal analysis, investigations, data validation and curation, writing the original draft, reviewing, and editing.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll the data obtained and or analyzed during the course of the study are included in this article.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePublication consent\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAuthor declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eQuint M, Delker C, Franklin KA, Wigge PA, Halliday KJ, van Zanten M. 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J Food Quality. 2021;9:ArticleID1159567.\u003c/li\u003e\n \u003cli\u003eDe Azevedo-Meleiro CH, SRodriguez-Amaya D. Carotenoids of endive and New Zealand spinach as affected by maturity, season and minimal processing. J. Food Compos. Anal. 2005;18:845\u0026ndash;855.\u003c/li\u003e\n \u003cli\u003eShen J, Jiang CQ, Yan YF, Liu BR, Zu C. Effect of increased UV-B radiation on carotenoid accumulation and total antioxidant capacity in tobacco (\u003cem\u003eNicotiana tabacum\u003c/em\u003e L.) leaves. Genet Mol. Res. 2017;16:1\u0026ndash;11.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Aquaponic greenhouse, β-Carotene biosynthesis, Food production, HPLC-Shimadzu Prominence, Leafy green spinach, Seasonal dynamics","lastPublishedDoi":"10.21203/rs.3.rs-5898385/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5898385/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe present study was conducted to determine the effects of seasonal dynamics in water temperature (WT) and electrical conductivity (EC) on β-Carotene biosynthesis in green spinach (GRSP) (Silver-beet) and green lettuce (GRLE) (Locarno) leaves from an aquaponic greenhouse. The WT and EC of the fish water tap (FWTP) and deep-water culture tank (DWCT) were assessed with a portable dissolved oxygen meter (Model: PDO-520, Taiwan) and a multi-parameter water quality meter (PHT-27, China), respectively. β-Carotene biosynthesis in GRSP and GRLE leaves was analyzed via HPLC-Shimadzu Prominence (Tokyo, Japan). This research was carried out for 4 consecutive seasons (winter, spring, autumn, and summer). The WT levels of the FWTP and DWCT components ranged from 12.12\u0026thinsp;\u0026plusmn;\u0026thinsp;1.34\u0026ndash;25.21\u0026thinsp;\u0026plusmn;\u0026thinsp;0.95\u0026deg;C. The EC values of these 2 components ranged from 0.55\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u0026ndash;0.65\u0026thinsp;\u0026plusmn;\u0026thinsp;0.55 mS/cm. The WT and EC values were significantly (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) different among the 4 seasons. Throughout the research period, the highest and lowest WT and EC levels were detected in the summer and winter periods, respectively. Furthermore, β-Carotene biosynthesis in the GRSP and GRLE leaves ranged from 3.63\u0026thinsp;\u0026plusmn;\u0026thinsp;0.27\u0026ndash;25.80\u0026thinsp;\u0026plusmn;\u0026thinsp;6.67%. A significant (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) difference in β-Carotene biosynthesis of the 2 leafy materials was recorded in the summer and autumn. However, no significant (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05) different was detected in the winter and spring. The highest level of β-Carotene biosynthesis was obtained in the summer. The results of the present study revealed that seasonal changes in WT and EC induced variations in β-Carotene biosynthesis in the studied vegetable materials. Hence, this work could be used to interpret better climate or growing conditions for sustainable food production.\u003c/p\u003e","manuscriptTitle":"Effect of Seasonal Dynamics in Water Temperature and Electrical Conductivity on β- Carotene Biosynthesis in Green Spinach (Silver-beet) and Lettuce (Locarno) Leaves from Aquaponic Greenhouse","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-01-31 06:29:22","doi":"10.21203/rs.3.rs-5898385/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"67b0514f-8d92-4da2-95f1-f4fbd4258d0c","owner":[],"postedDate":"January 31st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-04-17T04:08:28+00:00","versionOfRecord":[],"versionCreatedAt":"2025-01-31 06:29:22","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5898385","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5898385","identity":"rs-5898385","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}