Interactive effects of citric acid and tryptophan on cobalt bioavailability and oxidative stress responses in Salvia officinalis under controlled contamination conditions

Interactive effects of citric acid and tryptophan on cobalt bioavailability and oxidative stress responses in Salvia officinalis under controlled contamination conditions | 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 Interactive effects of citric acid and tryptophan on cobalt bioavailability and oxidative stress responses in Salvia officinalis under controlled contamination conditions Sareh Rezaie, Atousa Vaziri, Kobra Mahdavian This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9167832/v1 This work is licensed under a CC BY 4.0 License Status: Under Revision Version 1 posted 6 You are reading this latest preprint version Abstract The accumulation of cobalt (Co) in agricultural systems poses a serious threat to plant productivity, particularly in high-value medicinal species. This study evaluated the potential of exogenous citric acid (CA) and tryptophan (Trp), applied individually or in combination, to mitigate Co-induced phytotoxicity in hydroponically grown Salvia officinalis L. Plants were exposed to four Co concentrations (0, 1, 10, and 30 ppm) and four biostimulant treatments (control, 2 mM CA, 2 mM Trp, and CA + Trp) for four weeks. Increasing Co levels, especially 10 and 30 ppm, markedly impaired plant growth, biomass accumulation, and photosynthetic pigment contents (chlorophyll a, chlorophyll b, carotenoids, β-carotene, and anthocyanins). These effects were accompanied by enhanced lipid peroxidation, increased activities of antioxidant enzymes (CAT, POD, SOD, APX, and GPX), and significant disruption of primary metabolism, including reductions in soluble sugars, proteins, amino acids, malate, and oxalate. Application of CA or Trp alone partially alleviated Co toxicity; however, their combined application exerted a pronounced synergistic effect, resulting in substantial recovery of growth performance, photosynthetic capacity, and metabolic balance. Moreover, the combined treatment significantly reduced oxidative damage and moderated antioxidant enzyme activities, reflecting a lower oxidative burden, and limited Co accumulation in plant tissues. These findings suggest that CA may reduce Co bioavailability through chelation, while Trp likely enhances internal metabolic and antioxidative capacity. Their synergistic use represents an effective and sustainable biostimulant strategy to improve cobalt tolerance and ensure the safe production of medicinal plants under heavy metal stress in hydroponic systems. Salvia officinalis cobalt stress biostimulants oxidative stress antioxidant defense 1. Introduction The rapid expansion of industrial, mining, and intensive agricultural activities over recent decades has resulted in the widespread accumulation of heavy metals in soil and aquatic environments, posing a growing threat to ecosystem integrity, food safety, and sustainable agriculture (Cao et al., 2024 ; Wang et al., 2024 ; Chen et al., 2025 ). Among these contaminants, cobalt (Co) occupies a dual and complex position in plant systems. While trace amounts of Co (generally < 0.1–0.5 mg kg⁻¹) are considered beneficial for certain physiological processes, including enzyme activation and symbiotic nitrogen fixation in legumes, elevated concentrations arising from anthropogenic inputs rapidly induce toxicity (Mahey et al., 2020 ; Khalid et al., 2026 ). Excess cobalt primarily exerts its phytotoxic effects through the induction of oxidative stress. By interfering with electron transport processes and promoting redox cycling reactions, Co accelerates the generation of reactive oxygen species (ROS), including superoxide radicals (O₂•⁻), hydrogen peroxide (H₂O₂), and hydroxyl radicals (•OH) (Šiukšta et al., 2022 ; Salam et al., 2023 ). The overaccumulation of these reactive molecules leads to membrane lipid peroxidation, protein oxidation, nucleic acid damage, and degradation of photosynthetic pigments, ultimately manifesting as growth inhibition, biomass reduction, and impaired plant performance (Mahey et al., 2020 ). Consequently, developing effective and environmentally sound strategies to mitigate cobalt toxicity remains a critical research priority, particularly for high-value crop and medicinal plant production systems. Salvia officinalis L. (sage), a prominent member of the Lamiaceae family, is a widely cultivated medicinal plant valued for its rich content of bioactive compounds and well-documented antioxidant potential (Prakash et al., 2015 ). Sage is extensively utilized in pharmaceutical, food, and cosmetic industries; however, its growth and secondary metabolite production are highly sensitive to abiotic stresses, including heavy metal contamination (El Mahrouk et al., 2024 ). Hydroponic cultivation systems offer precise control over nutrient availability and root-zone conditions and are increasingly adopted for high-quality medicinal plant production. Nonetheless, the presence and accumulation of heavy metals such as cobalt in nutrient solutions can compromise both plant health and product safety, underscoring the need for effective mitigation strategies tailored to controlled cultivation systems. The application of biostimulants has emerged as a promising approach for alleviating heavy metal stress in plants. Organic acids and amino acids, in particular, play key roles in metal detoxification, redox regulation, and metabolic adjustment. Citric acid is a well-recognized organic chelator capable of forming stable complexes with metal cations, thereby reducing their bioavailability and mobility in the rhizosphere. Numerous studies have demonstrated that exogenous citric acid application enhances antioxidant capacity, limits lipid peroxidation, and improves growth performance in plants exposed to metals such as chromium, lead, zinc, and silver (Imran et al., 2019 ; Guo et al., 2021 ; Mahdavian, 2021 ; Mahdavian, 2022 ). Tryptophan, an essential amino acid and a key precursor of indole-3-acetic acid, has also been shown to contribute to plant stress tolerance beyond its nutritional role. Emerging evidence suggests that tryptophan can modulate plant growth and oxidative balance under heavy metal stress by influencing hormonal signaling, enhancing antioxidant defense systems, and participating in internal metal chelation processes (Jana et al., 2016 ; Mahdavian, 2023 ; Hussain et al., 2024 ). Despite substantial evidence supporting the individual roles of citric acid and amino acids in mitigating heavy metal toxicity, their combined or comparative effects on cobalt stress remain poorly understood. This knowledge gap is particularly evident for medicinal plants such as S. officinalis cultivated under hydroponic conditions, where metal bioavailability and oxidative responses can differ markedly from soil-based systems. Therefore, the present study aimed to evaluate the individual and combined effects of exogenous citric acid and tryptophan on cobalt-induced oxidative stress, growth inhibition, and physiological disruption in hydroponically grown Salvia officinalis . The findings are expected to provide mechanistic insights into biostimulant-mediated cobalt tolerance and to support the development of sustainable strategies for mitigating heavy metal risks in controlled medicinal plant production systems. 2. Materials and methods 2.1.Plant material, hydroponic system, and experimental design The experiment was conducted under controlled laboratory conditions using a deep water culture (DWC) hydroponic system. Certified seeds of sage ( Salvia officinalis L.) were surface-sterilized with 70% (v/v) ethanol for 1 min followed by 2% (v/v) sodium hypochlorite for 10 min and thoroughly rinsed with sterile distilled water. The seeds were germinated and grown in full-strength Hoagland nutrient solution. Plants were maintained under controlled environmental conditions (25 ± 2°C, 60–70% relative humidity, and a 16 h light/8 h dark photoperiod). At the six-leaf developmental stage, plants were subjected to cobalt (Co) treatments at four concentrations (0, 1, 10, and 30 mg L⁻¹) and biostimulant treatments consisting of control (no application), citric acid (CA, 2 mM), tryptophan (Trp, 2 mM), and their combined application (CA + Trp). Treatments were applied for four weeks. The experiment was arranged in a completely randomized factorial design with three biological replicates per treatment. 2.2.Growth measurements At harvest, plants were separated into shoots and roots. Fresh weight (FW) was recorded immediately, and dry weight (DW) was determined after oven-drying samples at 70°C for 48 h. Leaf number per plant was also recorded. 2.3.Determination of photosynthetic pigments Photosynthetic pigments were quantified following Lichtenthaler ( 1987 ). Briefly, 0.5 g of fresh leaf tissue was homogenized in 5 mL acetone, mixed with anhydrous sodium sulfate, filtered, and adjusted to a final volume of 10 mL. After centrifugation at 2600 rpm for 10 min, absorbance was measured at 662, 645, and 470 nm using a UV–Vis spectrophotometer. Chlorophyll a, chlorophyll b, total chlorophyll, and total carotenoids were expressed as mg g⁻¹ FW. 2.4.β-Carotene determination β-Carotene content was determined according to Hodisan et al. ( 1997 ). Fresh tissue (0.2 g) was extracted with an acetone–methanol–petroleum ether mixture under dark conditions, followed by saponification with 30% methanolic KOH. The non-saponifiable fraction was analyzed using an HPLC system (Knauer, Germany) equipped with a C18 column, with detection at 450 nm. 2.5.Anthocyanin content Total anthocyanins were measured following Mita et al. ( 1997 ). Dried leaf tissue (0.02 g) was extracted in methanol containing 1% HCl, incubated at 4°C for 24 h, and centrifuged. Absorbance was measured at 530 and 657 nm, and anthocyanin content was calculated as: A = A₅₃₀ − (0.25 × A₆₅₇). 2.6.Cobalt accumulation Cobalt concentration in shoot tissues was determined by atomic absorption spectrophotometry (Spectra AA 220, Australia) after nitric acid digestion, following Khan et al. ( 2009 ). Results were expressed as mg kg⁻¹ DW. 2.7.Antioxidant enzyme assays Fresh leaf tissue (0.5 g) was homogenized in ice-cold 50 mM phosphate buffer (pH 7.5) containing 1% polyvinylpyrrolidone and 1 mM EDTA. After centrifugation at 5000 rpm for 20 min at 4°C, the supernatant was used for enzyme activity assays. Ascorbate peroxidase (APX), catalase (CAT), superoxide dismutase (SOD), guaiacol peroxidase (GPX), and peroxidase (POD) activities were determined spectrophotometrically following standard protocols (Beauchamp and Fridovich, 1971 ; Dhindsa et al., 1981 ; Nakano and Asada, 1981 ; Upadhyaya et al., 1985 ; Wu et al., 2014 ). 2.8.Lipid peroxidation Malondialdehyde (MDA) content was measured using the thiobarbituric acid method (Heath and Packer, 1968 ), and concentrations were calculated using an extinction coefficient of 155 mM⁻¹ cm⁻¹. 2.9.Proline, soluble sugars, proteins, and free amino acids Proline content was determined according to Bates et al. ( 1973 ). Soluble sugars were measured using the anthrone method (Irigoyen et al., 1992 ). Protein concentration was quantified using the Bradford assay (Bradford, 1976 ), and total free amino acids were determined using the ninhydrin method (Ravindranath, 1981). 2.10.Organic acid analysis Organic acids (malate and oxalate) were quantified by HPLC following Tolrà et al. ( 1996 ). Fresh leaf tissue (0.2 g) was extracted with 0.025 M HCl, centrifuged, filtered, and analyzed at 210 nm using external standards for identification and quantification. 2.11.Statistical analysis Data were analyzed using SPSS v21. Two-way ANOVA was applied to evaluate main and interaction effects. Mean comparisons were performed using Tukey’s test at p < 0.05. 3. Results 3.1.Effects of protective treatments on growth and biomass of Salvia officinalis under cobalt stress Cobalt stress significantly affected the growth and biomass parameters of Salvia officinalis (Table 1 ). Increasing cobalt concentrations (10 and 30 ppm) caused a marked reduction in root fresh weight (FW), root dry weight (DW), shoot FW, and shoot DW compared with the control plants (***P < 0.001). Application of citric acid or tryptophan individually partially alleviated the inhibitory effects of cobalt stress on plant growth. However, the combined application of citric acid (2 ppm) and tryptophan (2 ppm) resulted in a pronounced improvement in all growth parameters across all cobalt levels. Notably, plants treated with citric acid + tryptophan under 30 ppm cobalt showed significantly higher biomass compared to cobalt-stressed plants without protective treatments (***P < 0.001). Under non-stress conditions, the combined treatment also significantly enhanced growth parameters compared with the control, indicating a synergistic stimulatory effect on plant biomass accumulation. 3.2.Effects of protective treatments on photosynthetic pigments under cobalt stress Cobalt toxicity significantly reduced chlorophyll, carotenoids, β-carotene, and anthocyanin contents in Salvia officinalis leaves, particularly at 10 and 30 ppm cobalt concentrations (Table 2 ). The reduction in photosynthetic pigments was highly significant compared with the control (***P < 0.001). Exogenous application of citric acid or tryptophan mitigated pigment degradation to some extent. Nevertheless, the combined application of citric acid and tryptophan was the most effective treatment, leading to a significant increase in chlorophyll and accessory pigments under both moderate and severe cobalt stress conditions (***P < 0.001). Under control conditions, plants receiving citric acid + tryptophan exhibited the highest pigment concentrations, suggesting an enhancement of photosynthetic capacity beyond stress alleviation. 3.3.Effects of protective treatments on oxidative stress marker (MDA) Malondialdehyde (MDA) content, an indicator of lipid peroxidation, increased significantly with increasing cobalt concentration (Table 3 ). The highest MDA levels were observed in plants exposed to 30 ppm cobalt, indicating severe oxidative damage (***P < 0.001). Application of citric acid or tryptophan significantly reduced MDA accumulation under cobalt stress. The lowest MDA content was recorded in plants treated with the combined citric acid and tryptophan treatment, even under high cobalt stress, demonstrating a strong protective effect against membrane lipid peroxidation (***P < 0.001). 3.4.Effects of protective treatments on antioxidant enzyme activities Cobalt stress induced a significant increase in antioxidant enzyme activities, including CAT, POD, SOD, APX, and GPX, compared with the control plants (Table 4 ). This increase was more pronounced at higher cobalt concentrations, reflecting an enhanced oxidative stress response. Protective treatments significantly modulated antioxidant enzyme activities. The combined application of citric acid and tryptophan resulted in a marked reduction in enzyme activities compared with cobalt-only treatments (***P < 0.001), indicating effective scavenging of reactive oxygen species and restoration of cellular redox balance. Under non-stress conditions, antioxidant enzyme activities were lower in treated plants compared with cobalt-stressed plants, suggesting that the protective treatments reduced the need for stress-induced enzymatic defense. 3.5.Effects of protective treatments on secondary metabolites and metal uptake Cobalt stress significantly decreased sugar, protein, amino acid, and organic acid contents, while increasing proline accumulation in Salvia officinalis (Table 5 ). In addition, cobalt uptake increased significantly with increasing cobalt concentration in the growth medium (***P < 0.001). Application of citric acid and tryptophan significantly enhanced the accumulation of primary and secondary metabolites under cobalt stress. The combined treatment showed the greatest increase in sugar, protein, amino acids, malate, oxalate, and proline contents. Moreover, plants treated with citric acid + tryptophan exhibited a significant reduction in cobalt uptake compared with untreated stressed plants, indicating a protective role in limiting metal accumulation. 4. Discussion The present study evaluated the potential of exogenous citric acid (CA) and tryptophan (Trp), applied individually and in combination, to mitigate cobalt (Co)-induced oxidative stress and to improve growth and physiological performance of Salvia officinalis L. cultivated in a hydroponic system. The results clearly demonstrate a concentration-dependent dual role of cobalt. At the lowest concentration tested (1 mg L⁻¹), Co exerted a mild stress that triggered a hormetic or defensive response, reflected by modest increases in antioxidant enzyme activities without marked growth inhibition. In contrast, higher concentrations (10 and 30 mg L⁻¹) imposed severe abiotic stress, leading to pronounced reductions in biomass accumulation, photosynthetic pigment content, and primary metabolic pools, accompanied by intense oxidative damage and hyperactivation of antioxidant defenses. A key outcome of this study is that both CA and Trp effectively alleviated these deleterious effects, with their combined application consistently conferring the greatest protection, particularly under moderate and severe Co stress. The strong inhibition of shoot and root growth under elevated Co levels is consistent with the well-established phytotoxicity of excess cobalt, which interferes with cell division, elongation, and nutrient uptake, ultimately constraining biomass production (Mahey et al., 2020 ; Jayakumar and Aksah, 2022 ). The substantial recovery of fresh and dry weights following CA and Trp application indicates that these compounds acted not only as stress mitigators but also as growth-promoting agents. Notably, the combined CA + Trp treatment restored growth parameters close to control levels under low Co stress and even enhanced biomass production in unstressed plants, highlighting a clear biostimulatory effect. Similar synergistic growth enhancement has been reported when chelating agents were combined with physiological modulators, as demonstrated by Mahdavian ( 2025 ), who showed that citric acid and EDTA jointly improved antioxidant regulation and metal handling in Peganum harmala exposed to lead stress. The superior performance of the combined treatment can be explained by complementary and interconnected mechanisms. Citric acid, as a low-molecular-weight organic acid, likely reduced the phytotoxicity of cobalt by chelating free Co²⁺ ions in the rhizosphere, thereby decreasing their bioavailability and limiting root uptake. Such chelation-mediated mitigation has been widely reported for various metals and plant species (Chen et al., 2003 ; Gaojie, 2019 ) and was previously documented by Mahdavian ( 2021 ), who showed that CA reduced chromium toxicity in red bean and garden cress by altering metal mobility and strengthening antioxidant responses. In parallel, tryptophan, as a precursor of indole-3-acetic acid (IAA), likely promoted cell division and elongation, counteracting the growth-suppressive effects of cobalt stress (Hussain et al., 2024 ). Beyond its role in auxin biosynthesis, Trp also contributes to nitrogen metabolism and serves as a precursor for detoxification-related compounds, including glutathione and phytochelatins. Mahdavian ( 2023 ) highlighted the importance of amino acid–derived detoxification pathways in conferring silver tolerance in P. harmala , supporting the notion that Trp enhances intracellular metal detoxification and metabolic resilience. Cobalt toxicity markedly impaired the photosynthetic apparatus, as evidenced by the dose-dependent decline in chlorophyll a, chlorophyll b, total carotenoids, and β-carotene. Such reductions are characteristic of heavy metal stress and are attributed to ROS-mediated pigment degradation, inhibition of chlorophyll biosynthetic enzymes, and disruption of chloroplast structure (Šiukšta et al., 2022 ). The application of CA and Trp, particularly in combination, effectively preserved pigment levels. The maintenance of carotenoids and β-carotene is of particular importance, as these pigments play a critical role in quenching singlet oxygen and protecting photosystems from photo-oxidative damage. Similar protective effects of organic acids on photosynthetic performance under metal stress have been reported previously, including the work of Mahdavian ( 2021 ), who observed improved pigment stability in red bean plants exposed to chromium stress following CA application. Preservation of photosynthetic capacity was closely associated with improved primary metabolism. Severe Co stress significantly reduced soluble sugar and protein contents, reflecting constraints on carbon assimilation and nitrogen metabolism. The restoration of these metabolites by CA and Trp treatments indicates improved metabolic efficiency and stress tolerance. Moreover, treated plants exhibited increased levels of total free amino acids, proline, malate, and oxalate. Proline accumulation is widely recognized as a protective response to abiotic stress, functioning as an osmoprotectant, ROS scavenger, and stabilizer of cellular structures (Koh et al., 2021 ). Malate and oxalate, on the other hand, are key organic acids involved in intracellular metal chelation and vacuolar sequestration. Mahdavian ( 2022 ) demonstrated that enhanced synthesis of organic acids and thiol-containing compounds played a central role in zinc detoxification in P. harmala , a mechanism that appears conserved in sage under cobalt stress. The elevated concentrations of these metabolites in CA + Trp-treated plants suggest a coordinated enhancement of osmotic adjustment, metabolic buffering, and internal metal detoxification. Oxidative stress emerged as a central component of cobalt toxicity, as indicated by the marked increase in malondialdehyde (MDA) content. Elevated activities of antioxidant enzymes, including CAT, SOD, POD, APX, and GPX, reflected the plant’s attempt to counteract excessive ROS production. However, such hyperactivation is energetically demanding and often insufficient to fully prevent cellular damage under high metal stress. Interestingly, CA and Trp application significantly reduced MDA levels while simultaneously lowering the activity of several antioxidant enzymes compared with untreated Co-stressed plants. This apparent paradox suggests that these treatments primarily reduced ROS generation rather than merely enhancing scavenging capacity. In other words, CA and Trp promoted stress mitigation rather than forcing the plant into a costly state of heightened defense. Citric acid likely reduced ROS production by chelating cobalt and limiting its participation in redox reactions, whereas Trp may have enhanced membrane stability and non-enzymatic antioxidant pools through its role in metabolic and hormonal regulation (Hussain et al., 2024 ). Comparable modulation of antioxidant defenses under reduced oxidative pressure was reported by Mahdavian ( 2022 , 2025 ) in studies on silver and lead stress, respectively. Taken together, the findings support a refined model in which CA and Trp operate through interconnected but distinct pathways. Citric acid primarily acts as an extracellular mitigator by reducing cobalt bioavailability and entry into plant tissues, while tryptophan functions mainly as an intracellular enhancer, sustaining growth, metabolism, and detoxification capacity. Their combination produces a synergistic effect by simultaneously addressing both the source of toxicity and its physiological consequences. This integrated strategy mirrors the multifaceted tolerance mechanisms observed in metal-accumulating species such as Peganum harmala (Mahdavian, 2025 ) and demonstrates its successful transfer to an economically important medicinal plant. From an applied perspective, these results have significant implications for the hydroponic cultivation of sage and other high-value medicinal plants in environments where nutrient solutions or water sources may be contaminated with trace metals. The combined use of citric acid and tryptophan represents a low-cost, environmentally friendly, and sustainable approach to safeguarding plant growth and physiological integrity under cobalt stress. Future research should focus on elucidating the molecular basis of this synergy by examining the expression of genes involved in metal transport, antioxidant defense, and auxin signaling. In addition, targeted metabolomic analyses are needed to determine whether stress mitigation also preserves or enhances the accumulation of key bioactive compounds, such as rosmarinic and salvianolic acids. Finally, validation of these findings under soil-based and field conditions will be essential to assess the long-term effectiveness and agronomic feasibility of this biostimulant strategy. 5. Conclusion In conclusion, this study elucidates that cobalt imposes significant oxidative stress and growth retardation on Salvia officinalis in a hydroponic system. Exogenous application of citric acid and tryptophan alleviates this stress through a synergistic dual-action model: citric acid primarily mitigates toxicity via extracellular chelation, reducing metal uptake and ROS initiation, while tryptophan enhances internal tolerance by supporting growth metabolism and antioxidant synthesis. Their combined application proved most effective, offering a promising, eco-friendly biostimulant strategy to enhance the resilience and productivity of medicinal plants in controlled agriculture facing heavy metal challenges. This work extends the foundational research on metal-plant interactions and detoxification mechanisms, exemplified by the studies of Mahdavian and colleagues on various species and metals, providing a validated strategy for improving crop performance under environmental stress. Declarations Acknowledgements We wish to thank Payame Noor University Research Council for approval and providing financial support. Funding This research did not receive any specific grant from funding agencies in the public, commercial, ornot-for-profit sectors. Authors’ Contributions S.R. performed all the experiments, acquisition of data, analysis and wrote the drafted manuscript. K.M. supervised all the experiments, contributing in data analysis, writing and revised the manuscript. A.V. designed research and supervised all the experiments sections as supervisor. Ethical Approval Not applicable. Consent to participate We consent to participate in this manuscript. 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J Plant Physiol 121(5):453–461 Wang M, Yu P, Tong Z, Shao X, Peng J, Hamid Y, Huang Y (2024) A modified model for quantitative heavy metal source apportionment and pollution pathway identification. Toxics 12(5):382. https://doi.org/10.3390/toxics12050382 Wu W, Wan X, Shah F, Fahad S, Huang J (2014) Oxidative stress and antioxidant enzyme activities in the rice plants under sheath blight stress. ScientificWorldJournal 2014:502134. https://doi.org/10.1155/2014/502134 Tables Table 1 Effects of cobalt stress and citric acid and tryptophan treatments on growth and biomass of Salvia officinalis . Shoot DW (g) Shoot FW (g) Root DW (g) Root FW (g) Treatments 0.727 ± 0.040 3.277 ± 0.176 0.350 ± 0.010 1.493 ± 0.131 Control 0.840 ± 0.010 3.473 ± 0.099 0.380 ± 0.017 1.657 ± 0.052 Control + citric acid 0.917 ± 0.081* 3.883 ± 0.090** 0.420 ± 0.000*** 1.793 ± 0.130 Control + tryptophan 1.217 ± 0.055*** 5.200 ± 0.124*** 0.573 ± 0.023*** 2.457 ± 0.032*** Control + combined treatment (citric acid + tryptophan) 0.687 ± 0.040 2.750 ± 0.132** 0.327 ± 0.012* 1.393 ± 0.075 Co 1 ppm 0.730 ± 0.034 3.097 ± 0.085 0.340 ± 0.010 1.430 ± 0.072 Co 1 ppm + citric acid 0.780 ± 0.023 3.483 ± 0.107* 0.387 ± 0.020* 1.613 ± 0.012 Co 1 ppm + tryptophan 1.103 ± 0.006*** 4.787 ± 0.095*** 0.513 ± 0.023*** 2.270 ± 0.092*** Co 1 ppm + combined treatment (citric acid + tryptophan) 0.540 ± 0.036*** 2.370 ± 0.052*** 0.237 ± 0.006*** 1.093 ± 0.114*** Co 10 ppm 0.563 ± 0.036 2.620 ± 0.152 0.270 ± 0.010* 1.187 ± 0.101 Co 10 ppm + citric acid 0.623 ± 0.078 2.703 ± 0.223 0.287 ± 0.032 1.243 ± 0.023 Co 10 ppm + tryptophan 0.853 ± 0.032*** 3.710 ± 0.165*** 0.413 ± 0.023*** 1.750 ± 0.096*** Co 10 ppm + combined treatment (citric acid + tryptophan) 0.397 ± 0.041*** 1.513 ± 0.174*** 0.173 ± 0.012*** 0.710 ± 0.050*** Co 30 ppm 0.420 ± 0.040 1.717 ± 0.080 0.193 ± 0.006 0.860 ± 0.086* Co 30 ppm + citric acid 0.400 ± 0.036 1.847 ± 0.025 0.200 ± 0.000 0.887 ± 0.130 Co 30 ppm + tryptophan 0.593 ± 0.026*** 2.573 ± 0.140*** 0.270 ± 0.010*** 1.157 ± 0.085*** Co 30 ppm + combined treatment (citric acid + tryptophan) Values are means ± SD (n = 3). *** p < 0.001, ** p < 0.01, * p < 0.05. FW fresh weight, DW dry weight Table 2 Effects of cobalt stress and citric acid and tryptophan treatments on photosynthetic pigments of Salvia officinalis . (mg/g)Anthocyanin β-carotene (mg/g) (mg/g) Carotenoid (mg/g)Chlorophyll Treatments 1.167 ± 0.035 1.007 ± 0.035 0.930 ± 0.010 2.530 ± 0.110 Control 1.287 ± 0.049 1.100 ± 0.030 0.967 ± 0.064 2.727 ± 0.081 Control + citric acid 1.423 ± 0.026** 1.200 ± 0.036* 1.057 ± 0.041* 2.950 ± 0.093* Control + tryptophan 1.930 ± 0.040*** 1.610 ± 0.031*** 1.460 ± 0.044*** 4.123 ± 0.138*** Control + combined treatment (citric acid + tryptophan) 1.103 ± 0.015 0.927 ± 0.060 0.730 ± 0.044** 2.293 ± 0.138 Co 1 ppm 1.180 ± 0.052 0.957 ± 0.006 0.883 ± 0.096 2.413 ± 0.141 Co 1 ppm + citric acid 1.273 ± 0.098 1.073 ± 0.043* 1.000 ± 0.065* 2.627 ± 0.037 Co 1 ppm + tryptophan 1.803 ± 0.062*** 1.440 ± 0.026*** 1.357 ± 0.087*** 3.660 ± 0.065*** Co 1 ppm + combined treatment (citric acid + tryptophan) 0.810 ± 0.082*** 0.710 ± 0.105*** 0.587 ± 0.085*** 1.687 ± 0.049*** Co 10 ppm 0.920 ± 0.030 0.767 ± 0.053 0.710 ± 0.055 1.797 ± 0.100 Co 10 ppm + citric acid 1.017 ± 0.032* 0.850 ± 0.075 0.763 ± 0.021* 2.170 ± 0.074** Co 10 ppm + tryptophan 1.400 ± 0.090*** 1.137 ± 0.035*** 1.070 ± 0.041*** 2.800 ± 0.104*** Co 10 ppm + combined treatment (citric acid + tryptophan) 0.637 ± 0.006*** 0.503 ± 0.021*** 0.467 ± 0.081*** 1.210 ± 0.032*** Co 30 ppm 0.630 ± 0.099 0.547 ± 0.055 0.477 ± 0.108 1.303 ± 0.072 Co 30 ppm + citric acid 0.727 ± 0.040 0.637 ± 0.031* 0.540 ± 0.038 1.497 ± 0.111** Co 30 ppm + tryptophan 1.020 ± 0.046*** 0.783 ± 0.023*** 0.787 ± 0.072*** 1.940 ± 0.135*** Co 30 ppm + combined treatment (citric acid + tryptophan) Values are means ± SD (n = 3). *** p < 0.001, ** p < 0.01, * p < 0.05. Table 3 Effects of cobalt stress and citric acid and tryptophan treatments on oxidative stress indices of Salvia officinalis . MDA (nmol/g) Treatments 1.200 ± 0.124 Control 1.010 ± 0.078* Control + citric acid 1.037 ± 0.058* Control + tryptophan 0.790 ± 0.019*** Control + combined treatment (citric acid + tryptophan) 1.300 ± 0.070 Co 1 ppm 1.167 ± 0.087 Co 1 ppm + citric acid 1.100 ± 0.036* Co 1 ppm + tryptophan 0.890 ± 0.033*** Co 1 ppm + combined treatment (citric acid + tryptophan) 1.800 ± 0.065*** Co 10 ppm 1.583 ± 0.082* Co 10 ppm + citric acid 1.433 ± 0.034*** Co 10 ppm + tryptophan 1.047 ± 0.066*** Co 10 ppm + combined treatment (citric acid + tryptophan) 2.393 ± 0.068*** Co 30 ppm 2.183 ± 0.072* Co 30 ppm + citric acid 2.030 ± 0.026*** Co 30 ppm + tryptophan 1.470 ± 0.000*** Co 30 ppm + combined treatment (citric acid + tryptophan) Values are means ± SD (n = 3). *** p < 0.001, ** p < 0.01, * p < 0.05. Table 4 Effects of cobalt stress and citric acid and tryptophan treatments on antioxidant enzyme activities of Salvia officinalis . GPX (U g⁻¹ FW) APX (U g⁻¹ FW) SOD (U g⁻¹ FW) POD (U g⁻¹ FW) CAT (U g⁻¹ FW) Treatments 7.85 ± 0.28 9.53 ± 0.25 24.98 ± 0.45 17.69 ± 0.44 20.02 ± 1.02 Control 7.76 ± 0.42 9.07 ± 0.83 22.37 ± 0.03*** 16.61 ± 1.08 17.68 ± 0.90* Control + citric acid 6.64 ± 0.50* 7.89 ± 0.40** 21.35 ± 0.99*** 14.57 ± 0.63*** 17.37 ± 0.97* Control + tryptophan 5.38 ± 0.83*** 6.51 ± 0.57*** 15.68 ± 1.15*** 11.52 ± 0.56*** 11.61 ± 0.99*** Control + combined treatment (citric acid + tryptophan) 8.74 ± 0.30 10.97 ± 0.24 27.58 ± 0.43 19.75 ± 0.68 23.18 ± 1.07 Co 1 ppm 8.33 ± 0.17 10.07 ± 0.44** 25.56 ± 0.75** 18.39 ± 0.68 20.69 ± 0.69* Co 1 ppm + citric acid 7.74 ± 0.56* 9.21 ± 0.65*** 23.30 ± 1.41*** 16.82 ± 0.69** 18.48 ± 0.27** Co 1 ppm + tryptophan 5.63 ± 0.51*** 6.71 ± 0.75*** 17.74 ± 1.26*** 12.44 ± 0.40*** 13.22 ± 1.43*** Co 1 ppm + combined treatment (citric acid + tryptophan) 11.31 ± 0.13*** 13.53 ± 0.43*** 35.02 ± 1.32*** 26.19 ± 0.35*** 28.86 ± 0.66*** Co 10 ppm 10.58 ± 0.74 12.96 ± 0.62 32.35 ± 1.24** 23.27 ± 0.42*** 26.38 ± 0.46** Co 10 ppm + citric acid 9.61 ± 0.53** 11.90 ± 0.44** 30.57 ± 0.78*** 21.88 ± 0.85*** 24.33 ± 0.59*** Co 10 ppm + tryptophan 7.29 ± 0.08*** 8.86 ± 0.40*** 20.54 ± 1.05*** 15.81 ± 0.45*** 17.08 ± 0.74*** Co 10 ppm + combined treatment (citric acid + tryptophan) 16.23 ± 0.42*** 20.44 ± 0.22*** 49.51 ± 1.45*** 36.45 ± 0.39*** 39.89 ± 0.67*** Co 30 ppm 14.16 ± 0.24*** 18.47 ± 0.27*** 46.87 ± 2.15 33.03 ± 0.41*** 35.71 ± 0.03*** Co 30 ppm + citric acid 13.08 ± 0.58*** 16.57 ± 0.67*** 41.53 ± 1.44*** 29.96 ± 0.37*** 33.69 ± 1.04*** Co 30 ppm + tryptophan 9.24 ± 0.20*** 12.39 ± 0.22*** 31.96 ± 2.28*** 21.74 ± 0.23*** 24.41 ± 0.58*** Co 30 ppm + combined treatment (citric acid + tryptophan) Values are means ± SD (n = 3). *** p < 0.001, ** p < 0.01, * p < 0.05. Table 5 Effects of cobalt stress and citric acid and tryptophan treatments on metabolic traits and cobalt accumulation of Salvia officinalis . Heavy metal absorption(mg g⁻¹) (µmol g⁻¹) Proline (mg g⁻¹) Oxalate (mg g⁻¹) Malate Total amino acids(mg g⁻¹) (mg g⁻¹) Protein (mg g⁻¹) Sugar Treatments 0.52 ± 0.06 1.43 ± 0.03 0.59 ± 0.04 0.68 ± 0.03 1.87 ± 0.07 2.48 ± 0.10 3.60 ± 0.02 Control 0.49 ± 0.06 1.56 ± 0.15 0.64 ± 0.03 0.76 ± 0.06* 1.88 ± 0.14 2.68 ± 0.08* 3.79 ± 0.20* Control + citric acid 0.52 ± 0.04 1.80 ± 0.15** 0.73 ± 0.04** 0.84 ± 0.05** 2.13 ± 0.09** 2.94 ± 0.11*** 4.21 ± 0.05*** Control + tryptophan 0.48 ± 0.04 2.41 ± 0.11*** 1.00 ± 0.03*** 1.13 ± 0.04*** 2.91 ± 0.10*** 4.08 ± 0.10*** 5.79 ± 0.06*** Control + combined treatment (citric acid + tryptophan) 0.48 ± 0.04 1.42 ± 0.04 0.53 ± 0.02 0.65 ± 0.04 1.61 ± 0.06 2.28 ± 0.12 3.14 ± 0.04 Co 1 ppm 0.48 ± 0.01 1.54 ± 0.04* 0.59 ± 0.02* 0.70 ± 0.04 1.68 ± 0.07 2.40 ± 0.05 3.54 ± 0.14** Co 1 ppm + citric acid 0.47 ± 0.04 1.64 ± 0.10** 0.63 ± 0.02*** 0.77 ± 0.02** 1.94 ± 0.05*** 2.65 ± 0.02*** 3.89 ± 0.21*** Co 1 ppm + tryptophan 0.49 ± 0.07 2.14 ± 0.13*** 0.89 ± 0.01*** 0.99 ± 0.02*** 2.63 ± 0.03*** 3.80 ± 0.16*** 5.14 ± 0.15*** Co 1 ppm + combined treatment (citric acid + tryptophan) 0.40 ± 0.04* 0.96 ± 0.08*** 0.42 ± 0.05*** 0.51 ± 0.03*** 1.28 ± 0.14*** 1.64 ± 0.05*** 2.54 ± 0.09*** Co 10 ppm 0.36 ± 0.02 1.13 ± 0.06* 0.48 ± 0.02 0.53 ± 0.04 1.31 ± 0.09 1.90 ± 0.03*** 2.70 ± 0.13 Co 10 ppm + citric acid 0.38 ± 0.05 1.28 ± 0.09** 0.52 ± 0.03** 0.61 ± 0.05* 1.55 ± 0.02** 2.03 ± 0.06*** 2.79 ± 0.10* Co 10 ppm + tryptophan 0.35 ± 0.05 1.73 ± 0.08*** 0.68 ± 0.02*** 0.80 ± 0.03*** 2.06 ± 0.12*** 2.76 ± 0.15*** 3.97 ± 0.08*** Co 10 ppm + combined treatment (citric acid + tryptophan) 0.23 ± 0.03*** 0.69 ± 0.09*** 0.32 ± 0.01*** 0.36 ± 0.01*** 0.98 ± 0.03*** 1.33 ± 0.06*** 1.79 ± 0.03*** Co 30 ppm 0.23 ± 0.09 0.88 ± 0.03** 0.30 ± 0.03 0.38 ± 0.02 0.97 ± 0.14 1.36 ± 0.12 1.87 ± 0.04 Co 30 ppm + citric acid 0.21 ± 0.02 0.94 ± 0.09* 0.34 ± 0.01 0.44 ± 0.03** 1.17 ± 0.08** 1.48 ± 0.13 2.23 ± 0.12*** Co 30 ppm + tryptophan 0.25 ± 0.01 1.24 ± 0.15*** 0.49 ± 0.05*** 0.58 ± 0.02*** 1.39 ± 0.05*** 2.03 ± 0.14*** 2.90 ± 0.12*** Co 30 ppm + combined treatment (citric acid + tryptophan) Values are means ± SD (n = 3). *** p < 0.001, ** p < 0.01, * p < 0.05. Cite Share Download PDF Status: Under Revision Version 1 posted Editorial decision: Major Revision 07 May, 2026 Reviewers agreed at journal 14 Apr, 2026 Reviewers invited by journal 14 Apr, 2026 Editor invited by journal 14 Apr, 2026 Editor assigned by journal 13 Apr, 2026 First submitted to journal 07 Apr, 2026 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-9167832","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":623256966,"identity":"1f2b23ed-61e0-408a-9600-b29b64ae0335","order_by":0,"name":"Sareh Rezaie","email":"","orcid":"","institution":"Payame Noor University","correspondingAuthor":false,"prefix":"","firstName":"Sareh","middleName":"","lastName":"Rezaie","suffix":""},{"id":623256968,"identity":"7ac5e0ba-96e8-434c-bf78-c2f7036d688d","order_by":1,"name":"Atousa Vaziri","email":"","orcid":"","institution":"Payame Noor University","correspondingAuthor":false,"prefix":"","firstName":"Atousa","middleName":"","lastName":"Vaziri","suffix":""},{"id":623256969,"identity":"2c4f0c82-0264-428f-b614-3395ca12c5c2","order_by":2,"name":"Kobra Mahdavian","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA5UlEQVRIiWNgGAWjYBACCSBmZmBjACHGBzDRA8RqYTYgTQsQsEkQ5TDJBu7EzwVldol97GePVRfuOMzA336A8XAFHi3SDLybpWecS05s48lLuz3zzGEGiTMJDAfP4NEix8C7QZq3jdmYjSHH7DZv22EGhhsMDAcb8GvZ/Ju3rd6Yjf+NWTFIizwhLUCHbQPacliOTSLHjBmkxYCQFslm3m3WPOeOA7W8MZae2ZbOY3gmsQGvFonjvZtv85RV88j35xh+LmyzlpM7fvjwR3xagJGCyuYBpgK8GnBrHwWjYBSMglEABwDgd0NVfZzPaQAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0001-8559-1601","institution":"Payame Noor University","correspondingAuthor":true,"prefix":"","firstName":"Kobra","middleName":"","lastName":"Mahdavian","suffix":""}],"badges":[],"createdAt":"2026-03-19 09:41:05","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9167832/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9167832/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":107706783,"identity":"9a16c762-7f10-4f52-96e4-30bd23d0986e","added_by":"auto","created_at":"2026-04-24 09:18:44","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":522174,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9167832/v1/c6e41d5e-50cb-45ab-8d05-33d5dfb907c5.pdf"}],"financialInterests":"","formattedTitle":"Interactive effects of citric acid and tryptophan on cobalt bioavailability and oxidative stress responses in Salvia officinalis under controlled contamination conditions","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe rapid expansion of industrial, mining, and intensive agricultural activities over recent decades has resulted in the widespread accumulation of heavy metals in soil and aquatic environments, posing a growing threat to ecosystem integrity, food safety, and sustainable agriculture (Cao et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Wang et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Chen et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Among these contaminants, cobalt (Co) occupies a dual and complex position in plant systems. While trace amounts of Co (generally\u0026thinsp;\u0026lt;\u0026thinsp;0.1\u0026ndash;0.5 mg kg⁻\u0026sup1;) are considered beneficial for certain physiological processes, including enzyme activation and symbiotic nitrogen fixation in legumes, elevated concentrations arising from anthropogenic inputs rapidly induce toxicity (Mahey et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Khalid et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2026\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eExcess cobalt primarily exerts its phytotoxic effects through the induction of oxidative stress. By interfering with electron transport processes and promoting redox cycling reactions, Co accelerates the generation of reactive oxygen species (ROS), including superoxide radicals (O₂\u0026bull;⁻), hydrogen peroxide (H₂O₂), and hydroxyl radicals (\u0026bull;OH) (Šiukšta et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Salam et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The overaccumulation of these reactive molecules leads to membrane lipid peroxidation, protein oxidation, nucleic acid damage, and degradation of photosynthetic pigments, ultimately manifesting as growth inhibition, biomass reduction, and impaired plant performance (Mahey et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Consequently, developing effective and environmentally sound strategies to mitigate cobalt toxicity remains a critical research priority, particularly for high-value crop and medicinal plant production systems.\u003c/p\u003e \u003cp\u003e \u003cem\u003eSalvia officinalis\u003c/em\u003e L. (sage), a prominent member of the Lamiaceae family, is a widely cultivated medicinal plant valued for its rich content of bioactive compounds and well-documented antioxidant potential (Prakash et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Sage is extensively utilized in pharmaceutical, food, and cosmetic industries; however, its growth and secondary metabolite production are highly sensitive to abiotic stresses, including heavy metal contamination (El Mahrouk et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Hydroponic cultivation systems offer precise control over nutrient availability and root-zone conditions and are increasingly adopted for high-quality medicinal plant production. Nonetheless, the presence and accumulation of heavy metals such as cobalt in nutrient solutions can compromise both plant health and product safety, underscoring the need for effective mitigation strategies tailored to controlled cultivation systems.\u003c/p\u003e \u003cp\u003eThe application of biostimulants has emerged as a promising approach for alleviating heavy metal stress in plants. Organic acids and amino acids, in particular, play key roles in metal detoxification, redox regulation, and metabolic adjustment. Citric acid is a well-recognized organic chelator capable of forming stable complexes with metal cations, thereby reducing their bioavailability and mobility in the rhizosphere. Numerous studies have demonstrated that exogenous citric acid application enhances antioxidant capacity, limits lipid peroxidation, and improves growth performance in plants exposed to metals such as chromium, lead, zinc, and silver (Imran et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Guo et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Mahdavian, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Mahdavian, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTryptophan, an essential amino acid and a key precursor of indole-3-acetic acid, has also been shown to contribute to plant stress tolerance beyond its nutritional role. Emerging evidence suggests that tryptophan can modulate plant growth and oxidative balance under heavy metal stress by influencing hormonal signaling, enhancing antioxidant defense systems, and participating in internal metal chelation processes (Jana et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Mahdavian, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Hussain et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eDespite substantial evidence supporting the individual roles of citric acid and amino acids in mitigating heavy metal toxicity, their combined or comparative effects on cobalt stress remain poorly understood. This knowledge gap is particularly evident for medicinal plants such as \u003cem\u003eS. officinalis\u003c/em\u003e cultivated under hydroponic conditions, where metal bioavailability and oxidative responses can differ markedly from soil-based systems.\u003c/p\u003e \u003cp\u003eTherefore, the present study aimed to evaluate the individual and combined effects of exogenous citric acid and tryptophan on cobalt-induced oxidative stress, growth inhibition, and physiological disruption in hydroponically grown \u003cem\u003eSalvia officinalis\u003c/em\u003e. The findings are expected to provide mechanistic insights into biostimulant-mediated cobalt tolerance and to support the development of sustainable strategies for mitigating heavy metal risks in controlled medicinal plant production systems.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1.Plant material, hydroponic system, and experimental design\u003c/h2\u003e \u003cp\u003eThe experiment was conducted under controlled laboratory conditions using a deep water culture (DWC) hydroponic system. Certified seeds of sage (\u003cem\u003eSalvia officinalis\u003c/em\u003e L.) were surface-sterilized with 70% (v/v) ethanol for 1 min followed by 2% (v/v) sodium hypochlorite for 10 min and thoroughly rinsed with sterile distilled water. The seeds were germinated and grown in full-strength Hoagland nutrient solution.\u003c/p\u003e \u003cp\u003ePlants were maintained under controlled environmental conditions (25\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u0026deg;C, 60\u0026ndash;70% relative humidity, and a 16 h light/8 h dark photoperiod). At the six-leaf developmental stage, plants were subjected to cobalt (Co) treatments at four concentrations (0, 1, 10, and 30 mg L⁻\u0026sup1;) and biostimulant treatments consisting of control (no application), citric acid (CA, 2 mM), tryptophan (Trp, 2 mM), and their combined application (CA\u0026thinsp;+\u0026thinsp;Trp). Treatments were applied for four weeks.\u003c/p\u003e \u003cp\u003eThe experiment was arranged in a completely randomized factorial design with three biological replicates per treatment.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2.Growth measurements\u003c/h2\u003e \u003cp\u003eAt harvest, plants were separated into shoots and roots. Fresh weight (FW) was recorded immediately, and dry weight (DW) was determined after oven-drying samples at 70\u0026deg;C for 48 h. Leaf number per plant was also recorded.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3.Determination of photosynthetic pigments\u003c/h2\u003e \u003cp\u003ePhotosynthetic pigments were quantified following Lichtenthaler (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1987\u003c/span\u003e). Briefly, 0.5 g of fresh leaf tissue was homogenized in 5 mL acetone, mixed with anhydrous sodium sulfate, filtered, and adjusted to a final volume of 10 mL. After centrifugation at 2600 rpm for 10 min, absorbance was measured at 662, 645, and 470 nm using a UV\u0026ndash;Vis spectrophotometer. Chlorophyll a, chlorophyll b, total chlorophyll, and total carotenoids were expressed as mg g⁻\u0026sup1; FW.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4.β-Carotene determination\u003c/h2\u003e \u003cp\u003eβ-Carotene content was determined according to Hodisan et al. (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e1997\u003c/span\u003e). Fresh tissue (0.2 g) was extracted with an acetone\u0026ndash;methanol\u0026ndash;petroleum ether mixture under dark conditions, followed by saponification with 30% methanolic KOH. The non-saponifiable fraction was analyzed using an HPLC system (Knauer, Germany) equipped with a C18 column, with detection at 450 nm.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5.Anthocyanin content\u003c/h2\u003e \u003cp\u003eTotal anthocyanins were measured following Mita et al. (\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1997\u003c/span\u003e). Dried leaf tissue (0.02 g) was extracted in methanol containing 1% HCl, incubated at 4\u0026deg;C for 24 h, and centrifuged. Absorbance was measured at 530 and 657 nm, and anthocyanin content was calculated as:\u003c/p\u003e \u003cp\u003eA\u0026thinsp;=\u0026thinsp;A₅₃₀ \u0026minus; (0.25 \u0026times; A₆₅₇).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.6.Cobalt accumulation\u003c/h2\u003e \u003cp\u003eCobalt concentration in shoot tissues was determined by atomic absorption spectrophotometry (Spectra AA 220, Australia) after nitric acid digestion, following Khan et al. (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Results were expressed as mg kg⁻\u0026sup1; DW.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e2.7.Antioxidant enzyme assays\u003c/h2\u003e \u003cp\u003eFresh leaf tissue (0.5 g) was homogenized in ice-cold 50 mM phosphate buffer (pH 7.5) containing 1% polyvinylpyrrolidone and 1 mM EDTA. After centrifugation at 5000 rpm for 20 min at 4\u0026deg;C, the supernatant was used for enzyme activity assays.\u003c/p\u003e \u003cp\u003eAscorbate peroxidase (APX), catalase (CAT), superoxide dismutase (SOD), guaiacol peroxidase (GPX), and peroxidase (POD) activities were determined spectrophotometrically following standard protocols (Beauchamp and Fridovich, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1971\u003c/span\u003e; Dhindsa et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1981\u003c/span\u003e; Nakano and Asada, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e1981\u003c/span\u003e; Upadhyaya et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e1985\u003c/span\u003e; Wu et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e2.8.Lipid peroxidation\u003c/h2\u003e \u003cp\u003eMalondialdehyde (MDA) content was measured using the thiobarbituric acid method (Heath and Packer, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1968\u003c/span\u003e), and concentrations were calculated using an extinction coefficient of 155 mM⁻\u0026sup1; cm⁻\u0026sup1;.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e2.9.Proline, soluble sugars, proteins, and free amino acids\u003c/h2\u003e \u003cp\u003eProline content was determined according to Bates et al. (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1973\u003c/span\u003e). Soluble sugars were measured using the anthrone method (Irigoyen et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e1992\u003c/span\u003e). Protein concentration was quantified using the Bradford assay (Bradford, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e1976\u003c/span\u003e), and total free amino acids were determined using the ninhydrin method (Ravindranath, 1981).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e2.10.Organic acid analysis\u003c/h2\u003e \u003cp\u003eOrganic acids (malate and oxalate) were quantified by HPLC following Tolr\u0026agrave; et al. (\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e1996\u003c/span\u003e). Fresh leaf tissue (0.2 g) was extracted with 0.025 M HCl, centrifuged, filtered, and analyzed at 210 nm using external standards for identification and quantification.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e2.11.Statistical analysis\u003c/h2\u003e \u003cp\u003eData were analyzed using SPSS v21. Two-way ANOVA was applied to evaluate main and interaction effects. Mean comparisons were performed using Tukey\u0026rsquo;s test at p\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e3.1.Effects of protective treatments on growth and biomass of \u003cem\u003eSalvia officinalis\u003c/em\u003e under cobalt stress\u003c/h2\u003e \u003cp\u003eCobalt stress significantly affected the growth and biomass parameters of \u003cem\u003eSalvia officinalis\u003c/em\u003e (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Increasing cobalt concentrations (10 and 30 ppm) caused a marked reduction in root fresh weight (FW), root dry weight (DW), shoot FW, and shoot DW compared with the control plants (***P\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e \u003cp\u003eApplication of citric acid or tryptophan individually partially alleviated the inhibitory effects of cobalt stress on plant growth. However, the combined application of citric acid (2 ppm) and tryptophan (2 ppm) resulted in a pronounced improvement in all growth parameters across all cobalt levels. Notably, plants treated with citric acid\u0026thinsp;+\u0026thinsp;tryptophan under 30 ppm cobalt showed significantly higher biomass compared to cobalt-stressed plants without protective treatments (***P\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e \u003cp\u003eUnder non-stress conditions, the combined treatment also significantly enhanced growth parameters compared with the control, indicating a synergistic stimulatory effect on plant biomass accumulation.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e3.2.Effects of protective treatments on photosynthetic pigments under cobalt stress\u003c/h2\u003e \u003cp\u003eCobalt toxicity significantly reduced chlorophyll, carotenoids, β-carotene, and anthocyanin contents in \u003cem\u003eSalvia officinalis\u003c/em\u003e leaves, particularly at 10 and 30 ppm cobalt concentrations (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The reduction in photosynthetic pigments was highly significant compared with the control (***P\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e \u003cp\u003eExogenous application of citric acid or tryptophan mitigated pigment degradation to some extent. Nevertheless, the combined application of citric acid and tryptophan was the most effective treatment, leading to a significant increase in chlorophyll and accessory pigments under both moderate and severe cobalt stress conditions (***P\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e \u003cp\u003eUnder control conditions, plants receiving citric acid\u0026thinsp;+\u0026thinsp;tryptophan exhibited the highest pigment concentrations, suggesting an enhancement of photosynthetic capacity beyond stress alleviation.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e3.3.Effects of protective treatments on oxidative stress marker (MDA)\u003c/h2\u003e \u003cp\u003eMalondialdehyde (MDA) content, an indicator of lipid peroxidation, increased significantly with increasing cobalt concentration (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The highest MDA levels were observed in plants exposed to 30 ppm cobalt, indicating severe oxidative damage (***P\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e \u003cp\u003eApplication of citric acid or tryptophan significantly reduced MDA accumulation under cobalt stress. The lowest MDA content was recorded in plants treated with the combined citric acid and tryptophan treatment, even under high cobalt stress, demonstrating a strong protective effect against membrane lipid peroxidation (***P\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e3.4.Effects of protective treatments on antioxidant enzyme activities\u003c/h2\u003e \u003cp\u003eCobalt stress induced a significant increase in antioxidant enzyme activities, including CAT, POD, SOD, APX, and GPX, compared with the control plants (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). This increase was more pronounced at higher cobalt concentrations, reflecting an enhanced oxidative stress response.\u003c/p\u003e \u003cp\u003eProtective treatments significantly modulated antioxidant enzyme activities. The combined application of citric acid and tryptophan resulted in a marked reduction in enzyme activities compared with cobalt-only treatments (***P\u0026thinsp;\u0026lt;\u0026thinsp;0.001), indicating effective scavenging of reactive oxygen species and restoration of cellular redox balance.\u003c/p\u003e \u003cp\u003eUnder non-stress conditions, antioxidant enzyme activities were lower in treated plants compared with cobalt-stressed plants, suggesting that the protective treatments reduced the need for stress-induced enzymatic defense.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e3.5.Effects of protective treatments on secondary metabolites and metal uptake\u003c/h2\u003e \u003cp\u003eCobalt stress significantly decreased sugar, protein, amino acid, and organic acid contents, while increasing proline accumulation in \u003cem\u003eSalvia officinalis\u003c/em\u003e (Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). In addition, cobalt uptake increased significantly with increasing cobalt concentration in the growth medium (***P\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e \u003cp\u003eApplication of citric acid and tryptophan significantly enhanced the accumulation of primary and secondary metabolites under cobalt stress. The combined treatment showed the greatest increase in sugar, protein, amino acids, malate, oxalate, and proline contents. Moreover, plants treated with citric acid\u0026thinsp;+\u0026thinsp;tryptophan exhibited a significant reduction in cobalt uptake compared with untreated stressed plants, indicating a protective role in limiting metal accumulation.\u003c/p\u003e "},{"header":"4. Discussion","content":"\u003cp\u003eThe present study evaluated the potential of exogenous citric acid (CA) and tryptophan (Trp), applied individually and in combination, to mitigate cobalt (Co)-induced oxidative stress and to improve growth and physiological performance of \u003cem\u003eSalvia officinalis\u003c/em\u003e L. cultivated in a hydroponic system. The results clearly demonstrate a concentration-dependent dual role of cobalt. At the lowest concentration tested (1 mg L⁻\u0026sup1;), Co exerted a mild stress that triggered a hormetic or defensive response, reflected by modest increases in antioxidant enzyme activities without marked growth inhibition. In contrast, higher concentrations (10 and 30 mg L⁻\u0026sup1;) imposed severe abiotic stress, leading to pronounced reductions in biomass accumulation, photosynthetic pigment content, and primary metabolic pools, accompanied by intense oxidative damage and hyperactivation of antioxidant defenses. A key outcome of this study is that both CA and Trp effectively alleviated these deleterious effects, with their combined application consistently conferring the greatest protection, particularly under moderate and severe Co stress.\u003c/p\u003e \u003cp\u003eThe strong inhibition of shoot and root growth under elevated Co levels is consistent with the well-established phytotoxicity of excess cobalt, which interferes with cell division, elongation, and nutrient uptake, ultimately constraining biomass production (Mahey et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Jayakumar and Aksah, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The substantial recovery of fresh and dry weights following CA and Trp application indicates that these compounds acted not only as stress mitigators but also as growth-promoting agents. Notably, the combined CA\u0026thinsp;+\u0026thinsp;Trp treatment restored growth parameters close to control levels under low Co stress and even enhanced biomass production in unstressed plants, highlighting a clear biostimulatory effect. Similar synergistic growth enhancement has been reported when chelating agents were combined with physiological modulators, as demonstrated by Mahdavian (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2025\u003c/span\u003e), who showed that citric acid and EDTA jointly improved antioxidant regulation and metal handling in \u003cem\u003ePeganum harmala\u003c/em\u003e exposed to lead stress.\u003c/p\u003e \u003cp\u003eThe superior performance of the combined treatment can be explained by complementary and interconnected mechanisms. Citric acid, as a low-molecular-weight organic acid, likely reduced the phytotoxicity of cobalt by chelating free Co\u0026sup2;⁺ ions in the rhizosphere, thereby decreasing their bioavailability and limiting root uptake. Such chelation-mediated mitigation has been widely reported for various metals and plant species (Chen et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Gaojie, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) and was previously documented by Mahdavian (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), who showed that CA reduced chromium toxicity in red bean and garden cress by altering metal mobility and strengthening antioxidant responses. In parallel, tryptophan, as a precursor of indole-3-acetic acid (IAA), likely promoted cell division and elongation, counteracting the growth-suppressive effects of cobalt stress (Hussain et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Beyond its role in auxin biosynthesis, Trp also contributes to nitrogen metabolism and serves as a precursor for detoxification-related compounds, including glutathione and phytochelatins. Mahdavian (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) highlighted the importance of amino acid\u0026ndash;derived detoxification pathways in conferring silver tolerance in \u003cem\u003eP. harmala\u003c/em\u003e, supporting the notion that Trp enhances intracellular metal detoxification and metabolic resilience.\u003c/p\u003e \u003cp\u003eCobalt toxicity markedly impaired the photosynthetic apparatus, as evidenced by the dose-dependent decline in chlorophyll a, chlorophyll b, total carotenoids, and β-carotene. Such reductions are characteristic of heavy metal stress and are attributed to ROS-mediated pigment degradation, inhibition of chlorophyll biosynthetic enzymes, and disruption of chloroplast structure (Šiukšta et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The application of CA and Trp, particularly in combination, effectively preserved pigment levels. The maintenance of carotenoids and β-carotene is of particular importance, as these pigments play a critical role in quenching singlet oxygen and protecting photosystems from photo-oxidative damage. Similar protective effects of organic acids on photosynthetic performance under metal stress have been reported previously, including the work of Mahdavian (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), who observed improved pigment stability in red bean plants exposed to chromium stress following CA application.\u003c/p\u003e \u003cp\u003ePreservation of photosynthetic capacity was closely associated with improved primary metabolism. Severe Co stress significantly reduced soluble sugar and protein contents, reflecting constraints on carbon assimilation and nitrogen metabolism. The restoration of these metabolites by CA and Trp treatments indicates improved metabolic efficiency and stress tolerance. Moreover, treated plants exhibited increased levels of total free amino acids, proline, malate, and oxalate. Proline accumulation is widely recognized as a protective response to abiotic stress, functioning as an osmoprotectant, ROS scavenger, and stabilizer of cellular structures (Koh et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Malate and oxalate, on the other hand, are key organic acids involved in intracellular metal chelation and vacuolar sequestration. Mahdavian (\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) demonstrated that enhanced synthesis of organic acids and thiol-containing compounds played a central role in zinc detoxification in \u003cem\u003eP. harmala\u003c/em\u003e, a mechanism that appears conserved in sage under cobalt stress. The elevated concentrations of these metabolites in CA\u0026thinsp;+\u0026thinsp;Trp-treated plants suggest a coordinated enhancement of osmotic adjustment, metabolic buffering, and internal metal detoxification.\u003c/p\u003e \u003cp\u003eOxidative stress emerged as a central component of cobalt toxicity, as indicated by the marked increase in malondialdehyde (MDA) content. Elevated activities of antioxidant enzymes, including CAT, SOD, POD, APX, and GPX, reflected the plant\u0026rsquo;s attempt to counteract excessive ROS production. However, such hyperactivation is energetically demanding and often insufficient to fully prevent cellular damage under high metal stress. Interestingly, CA and Trp application significantly reduced MDA levels while simultaneously lowering the activity of several antioxidant enzymes compared with untreated Co-stressed plants. This apparent paradox suggests that these treatments primarily reduced ROS generation rather than merely enhancing scavenging capacity. In other words, CA and Trp promoted stress mitigation rather than forcing the plant into a costly state of heightened defense. Citric acid likely reduced ROS production by chelating cobalt and limiting its participation in redox reactions, whereas Trp may have enhanced membrane stability and non-enzymatic antioxidant pools through its role in metabolic and hormonal regulation (Hussain et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Comparable modulation of antioxidant defenses under reduced oxidative pressure was reported by Mahdavian (\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2022\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2025\u003c/span\u003e) in studies on silver and lead stress, respectively.\u003c/p\u003e \u003cp\u003eTaken together, the findings support a refined model in which CA and Trp operate through interconnected but distinct pathways. Citric acid primarily acts as an extracellular mitigator by reducing cobalt bioavailability and entry into plant tissues, while tryptophan functions mainly as an intracellular enhancer, sustaining growth, metabolism, and detoxification capacity. Their combination produces a synergistic effect by simultaneously addressing both the source of toxicity and its physiological consequences. This integrated strategy mirrors the multifaceted tolerance mechanisms observed in metal-accumulating species such as \u003cem\u003ePeganum harmala\u003c/em\u003e (Mahdavian, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2025\u003c/span\u003e) and demonstrates its successful transfer to an economically important medicinal plant.\u003c/p\u003e \u003cp\u003eFrom an applied perspective, these results have significant implications for the hydroponic cultivation of sage and other high-value medicinal plants in environments where nutrient solutions or water sources may be contaminated with trace metals. The combined use of citric acid and tryptophan represents a low-cost, environmentally friendly, and sustainable approach to safeguarding plant growth and physiological integrity under cobalt stress. Future research should focus on elucidating the molecular basis of this synergy by examining the expression of genes involved in metal transport, antioxidant defense, and auxin signaling. In addition, targeted metabolomic analyses are needed to determine whether stress mitigation also preserves or enhances the accumulation of key bioactive compounds, such as rosmarinic and salvianolic acids. Finally, validation of these findings under soil-based and field conditions will be essential to assess the long-term effectiveness and agronomic feasibility of this biostimulant strategy.\u003c/p\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eIn conclusion, this study elucidates that cobalt imposes significant oxidative stress and growth retardation on \u003cem\u003eSalvia officinalis\u003c/em\u003e in a hydroponic system. Exogenous application of citric acid and tryptophan alleviates this stress through a synergistic dual-action model: citric acid primarily mitigates toxicity via extracellular chelation, reducing metal uptake and ROS initiation, while tryptophan enhances internal tolerance by supporting growth metabolism and antioxidant synthesis. Their combined application proved most effective, offering a promising, eco-friendly biostimulant strategy to enhance the resilience and productivity of medicinal plants in controlled agriculture facing heavy metal challenges. This work extends the foundational research on metal-plant interactions and detoxification mechanisms, exemplified by the studies of Mahdavian and colleagues on various species and metals, providing a validated strategy for improving crop performance under environmental stress.\u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe wish to thank Payame Noor University Research Council for approval and providing financial support.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research did not receive any specific grant from funding agencies in the public, commercial, ornot-for-profit sectors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo; Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eS.R. performed all the experiments, acquisition of data, analysis and wrote the drafted manuscript. K.M. supervised all the experiments, contributing in data analysis, writing and revised the manuscript. A.V. designed research and supervised all the experiments sections as supervisor.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical Approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to participate\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eWe consent to participate in this manuscript.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Publish\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors have reviewed the manuscript and consent to its publication.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated during the current study are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBates LS, Waldren RP, Teare ID (1973) Rapid determination of free proline for water stress studies. Plant Soil 39(1):205\u0026ndash;207\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBeauchamp C, Fridovich I (1971) Superoxide dismutase: improved assays and an assay applicable to acrylamide gels. Anal Biochem 44(1):276\u0026ndash;287\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBradford MM (1976) A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein dye binding. Anal Biochem 72(1\u0026ndash;2):248\u0026ndash;254\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCao M, Jia Y, Lu X, Huang J, Yao Y, Hong L, Zhu W, Wang W, Zhu F, Hong C (2024) Temporal and spatial variation of toxic metal concentrations in cultivated soil in Jiaxing, Zhejiang Province, China: characteristics and mechanisms. 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ScientificWorldJournal 2014:502134. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1155/2014/502134\u003c/span\u003e\u003cspan address=\"10.1155/2014/502134\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEffects of cobalt stress and citric acid and tryptophan treatments on growth and biomass of \u003cem\u003eSalvia officinalis\u003c/em\u003e.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eShoot DW (g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eShoot FW (g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRoot DW (g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRoot FW (g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTreatments\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.727\u0026thinsp;\u0026plusmn;\u0026thinsp;0.040\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e3.277\u0026thinsp;\u0026plusmn;\u0026thinsp;0.176\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.350\u0026thinsp;\u0026plusmn;\u0026thinsp;0.010\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1.493\u0026thinsp;\u0026plusmn;\u0026thinsp;0.131\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eControl\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.840\u0026thinsp;\u0026plusmn;\u0026thinsp;0.010\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e3.473\u0026thinsp;\u0026plusmn;\u0026thinsp;0.099\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.380\u0026thinsp;\u0026plusmn;\u0026thinsp;0.017\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1.657\u0026thinsp;\u0026plusmn;\u0026thinsp;0.052\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eControl\u0026thinsp;+\u0026thinsp;citric acid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.917\u0026thinsp;\u0026plusmn;\u0026thinsp;0.081*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e3.883\u0026thinsp;\u0026plusmn;\u0026thinsp;0.090**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.420\u0026thinsp;\u0026plusmn;\u0026thinsp;0.000***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1.793\u0026thinsp;\u0026plusmn;\u0026thinsp;0.130\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eControl\u0026thinsp;+\u0026thinsp;tryptophan\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.217\u0026thinsp;\u0026plusmn;\u0026thinsp;0.055***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e5.200\u0026thinsp;\u0026plusmn;\u0026thinsp;0.124***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.573\u0026thinsp;\u0026plusmn;\u0026thinsp;0.023***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e2.457\u0026thinsp;\u0026plusmn;\u0026thinsp;0.032***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eControl\u0026thinsp;+\u0026thinsp;combined treatment (citric acid\u0026thinsp;+\u0026thinsp;tryptophan)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.687\u0026thinsp;\u0026plusmn;\u0026thinsp;0.040\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e2.750\u0026thinsp;\u0026plusmn;\u0026thinsp;0.132**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.327\u0026thinsp;\u0026plusmn;\u0026thinsp;0.012*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1.393\u0026thinsp;\u0026plusmn;\u0026thinsp;0.075\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCo 1 ppm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.730\u0026thinsp;\u0026plusmn;\u0026thinsp;0.034\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e3.097\u0026thinsp;\u0026plusmn;\u0026thinsp;0.085\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.340\u0026thinsp;\u0026plusmn;\u0026thinsp;0.010\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1.430\u0026thinsp;\u0026plusmn;\u0026thinsp;0.072\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCo 1 ppm\u0026thinsp;+\u0026thinsp;citric acid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.780\u0026thinsp;\u0026plusmn;\u0026thinsp;0.023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e3.483\u0026thinsp;\u0026plusmn;\u0026thinsp;0.107*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.387\u0026thinsp;\u0026plusmn;\u0026thinsp;0.020*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1.613\u0026thinsp;\u0026plusmn;\u0026thinsp;0.012\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCo 1 ppm\u0026thinsp;+\u0026thinsp;tryptophan\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.103\u0026thinsp;\u0026plusmn;\u0026thinsp;0.006***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e4.787\u0026thinsp;\u0026plusmn;\u0026thinsp;0.095***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.513\u0026thinsp;\u0026plusmn;\u0026thinsp;0.023***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e2.270\u0026thinsp;\u0026plusmn;\u0026thinsp;0.092***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCo 1 ppm\u0026thinsp;+\u0026thinsp;combined treatment (citric acid\u0026thinsp;+\u0026thinsp;tryptophan)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.540\u0026thinsp;\u0026plusmn;\u0026thinsp;0.036***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e2.370\u0026thinsp;\u0026plusmn;\u0026thinsp;0.052***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.237\u0026thinsp;\u0026plusmn;\u0026thinsp;0.006***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1.093\u0026thinsp;\u0026plusmn;\u0026thinsp;0.114***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCo 10 ppm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.563\u0026thinsp;\u0026plusmn;\u0026thinsp;0.036\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e2.620\u0026thinsp;\u0026plusmn;\u0026thinsp;0.152\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.270\u0026thinsp;\u0026plusmn;\u0026thinsp;0.010*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1.187\u0026thinsp;\u0026plusmn;\u0026thinsp;0.101\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCo 10 ppm\u0026thinsp;+\u0026thinsp;citric acid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.623\u0026thinsp;\u0026plusmn;\u0026thinsp;0.078\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e2.703\u0026thinsp;\u0026plusmn;\u0026thinsp;0.223\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.287\u0026thinsp;\u0026plusmn;\u0026thinsp;0.032\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1.243\u0026thinsp;\u0026plusmn;\u0026thinsp;0.023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCo 10 ppm\u0026thinsp;+\u0026thinsp;tryptophan\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.853\u0026thinsp;\u0026plusmn;\u0026thinsp;0.032***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e3.710\u0026thinsp;\u0026plusmn;\u0026thinsp;0.165***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.413\u0026thinsp;\u0026plusmn;\u0026thinsp;0.023***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1.750\u0026thinsp;\u0026plusmn;\u0026thinsp;0.096***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCo 10 ppm\u0026thinsp;+\u0026thinsp;combined treatment (citric acid\u0026thinsp;+\u0026thinsp;tryptophan)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.397\u0026thinsp;\u0026plusmn;\u0026thinsp;0.041***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.513\u0026thinsp;\u0026plusmn;\u0026thinsp;0.174***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.173\u0026thinsp;\u0026plusmn;\u0026thinsp;0.012***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.710\u0026thinsp;\u0026plusmn;\u0026thinsp;0.050***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCo 30 ppm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.420\u0026thinsp;\u0026plusmn;\u0026thinsp;0.040\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.717\u0026thinsp;\u0026plusmn;\u0026thinsp;0.080\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.193\u0026thinsp;\u0026plusmn;\u0026thinsp;0.006\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.860\u0026thinsp;\u0026plusmn;\u0026thinsp;0.086*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCo 30 ppm\u0026thinsp;+\u0026thinsp;citric acid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.400\u0026thinsp;\u0026plusmn;\u0026thinsp;0.036\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.847\u0026thinsp;\u0026plusmn;\u0026thinsp;0.025\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.200\u0026thinsp;\u0026plusmn;\u0026thinsp;0.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.887\u0026thinsp;\u0026plusmn;\u0026thinsp;0.130\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCo 30 ppm\u0026thinsp;+\u0026thinsp;tryptophan\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.593\u0026thinsp;\u0026plusmn;\u0026thinsp;0.026***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e2.573\u0026thinsp;\u0026plusmn;\u0026thinsp;0.140***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.270\u0026thinsp;\u0026plusmn;\u0026thinsp;0.010***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1.157\u0026thinsp;\u0026plusmn;\u0026thinsp;0.085***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCo 30 ppm\u0026thinsp;+\u0026thinsp;combined treatment (citric acid\u0026thinsp;+\u0026thinsp;tryptophan)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eValues are means\u0026thinsp;\u0026plusmn;\u0026thinsp;SD (n\u0026thinsp;=\u0026thinsp;3). *** p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, ** p\u0026thinsp;\u0026lt;\u0026thinsp;0.01, * p\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003cp\u003eFW fresh weight, DW dry weight\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\u003eEffects of cobalt stress and citric acid and tryptophan treatments on photosynthetic pigments of \u003cem\u003eSalvia officinalis\u003c/em\u003e.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003e(mg/g)Anthocyanin\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eβ-carotene (mg/g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(mg/g) Carotenoid\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e(mg/g)Chlorophyll\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTreatments\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.167\u0026thinsp;\u0026plusmn;\u0026thinsp;0.035\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.007\u0026thinsp;\u0026plusmn;\u0026thinsp;0.035\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.930\u0026thinsp;\u0026plusmn;\u0026thinsp;0.010\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e2.530\u0026thinsp;\u0026plusmn;\u0026thinsp;0.110\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eControl\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.287\u0026thinsp;\u0026plusmn;\u0026thinsp;0.049\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.100\u0026thinsp;\u0026plusmn;\u0026thinsp;0.030\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.967\u0026thinsp;\u0026plusmn;\u0026thinsp;0.064\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e2.727\u0026thinsp;\u0026plusmn;\u0026thinsp;0.081\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eControl\u0026thinsp;+\u0026thinsp;citric acid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.423\u0026thinsp;\u0026plusmn;\u0026thinsp;0.026**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.200\u0026thinsp;\u0026plusmn;\u0026thinsp;0.036*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e1.057\u0026thinsp;\u0026plusmn;\u0026thinsp;0.041*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e2.950\u0026thinsp;\u0026plusmn;\u0026thinsp;0.093*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eControl\u0026thinsp;+\u0026thinsp;tryptophan\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.930\u0026thinsp;\u0026plusmn;\u0026thinsp;0.040***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.610\u0026thinsp;\u0026plusmn;\u0026thinsp;0.031***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e1.460\u0026thinsp;\u0026plusmn;\u0026thinsp;0.044***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e4.123\u0026thinsp;\u0026plusmn;\u0026thinsp;0.138***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eControl\u0026thinsp;+\u0026thinsp;combined treatment (citric acid\u0026thinsp;+\u0026thinsp;tryptophan)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.103\u0026thinsp;\u0026plusmn;\u0026thinsp;0.015\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.927\u0026thinsp;\u0026plusmn;\u0026thinsp;0.060\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.730\u0026thinsp;\u0026plusmn;\u0026thinsp;0.044**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e2.293\u0026thinsp;\u0026plusmn;\u0026thinsp;0.138\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCo 1 ppm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.180\u0026thinsp;\u0026plusmn;\u0026thinsp;0.052\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.957\u0026thinsp;\u0026plusmn;\u0026thinsp;0.006\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.883\u0026thinsp;\u0026plusmn;\u0026thinsp;0.096\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e2.413\u0026thinsp;\u0026plusmn;\u0026thinsp;0.141\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCo 1 ppm\u0026thinsp;+\u0026thinsp;citric acid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.273\u0026thinsp;\u0026plusmn;\u0026thinsp;0.098\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.073\u0026thinsp;\u0026plusmn;\u0026thinsp;0.043*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e1.000\u0026thinsp;\u0026plusmn;\u0026thinsp;0.065*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e2.627\u0026thinsp;\u0026plusmn;\u0026thinsp;0.037\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCo 1 ppm\u0026thinsp;+\u0026thinsp;tryptophan\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.803\u0026thinsp;\u0026plusmn;\u0026thinsp;0.062***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.440\u0026thinsp;\u0026plusmn;\u0026thinsp;0.026***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e1.357\u0026thinsp;\u0026plusmn;\u0026thinsp;0.087***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e3.660\u0026thinsp;\u0026plusmn;\u0026thinsp;0.065***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCo 1 ppm\u0026thinsp;+\u0026thinsp;combined treatment (citric acid\u0026thinsp;+\u0026thinsp;tryptophan)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.810\u0026thinsp;\u0026plusmn;\u0026thinsp;0.082***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.710\u0026thinsp;\u0026plusmn;\u0026thinsp;0.105***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.587\u0026thinsp;\u0026plusmn;\u0026thinsp;0.085***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1.687\u0026thinsp;\u0026plusmn;\u0026thinsp;0.049***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCo 10 ppm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.920\u0026thinsp;\u0026plusmn;\u0026thinsp;0.030\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.767\u0026thinsp;\u0026plusmn;\u0026thinsp;0.053\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.710\u0026thinsp;\u0026plusmn;\u0026thinsp;0.055\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1.797\u0026thinsp;\u0026plusmn;\u0026thinsp;0.100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCo 10 ppm\u0026thinsp;+\u0026thinsp;citric acid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.017\u0026thinsp;\u0026plusmn;\u0026thinsp;0.032*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.850\u0026thinsp;\u0026plusmn;\u0026thinsp;0.075\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.763\u0026thinsp;\u0026plusmn;\u0026thinsp;0.021*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e2.170\u0026thinsp;\u0026plusmn;\u0026thinsp;0.074**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCo 10 ppm\u0026thinsp;+\u0026thinsp;tryptophan\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.400\u0026thinsp;\u0026plusmn;\u0026thinsp;0.090***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.137\u0026thinsp;\u0026plusmn;\u0026thinsp;0.035***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e1.070\u0026thinsp;\u0026plusmn;\u0026thinsp;0.041***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e2.800\u0026thinsp;\u0026plusmn;\u0026thinsp;0.104***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCo 10 ppm\u0026thinsp;+\u0026thinsp;combined treatment (citric acid\u0026thinsp;+\u0026thinsp;tryptophan)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.637\u0026thinsp;\u0026plusmn;\u0026thinsp;0.006***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.503\u0026thinsp;\u0026plusmn;\u0026thinsp;0.021***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.467\u0026thinsp;\u0026plusmn;\u0026thinsp;0.081***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1.210\u0026thinsp;\u0026plusmn;\u0026thinsp;0.032***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCo 30 ppm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.630\u0026thinsp;\u0026plusmn;\u0026thinsp;0.099\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.547\u0026thinsp;\u0026plusmn;\u0026thinsp;0.055\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.477\u0026thinsp;\u0026plusmn;\u0026thinsp;0.108\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1.303\u0026thinsp;\u0026plusmn;\u0026thinsp;0.072\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCo 30 ppm\u0026thinsp;+\u0026thinsp;citric acid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.727\u0026thinsp;\u0026plusmn;\u0026thinsp;0.040\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.637\u0026thinsp;\u0026plusmn;\u0026thinsp;0.031*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.540\u0026thinsp;\u0026plusmn;\u0026thinsp;0.038\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1.497\u0026thinsp;\u0026plusmn;\u0026thinsp;0.111**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCo 30 ppm\u0026thinsp;+\u0026thinsp;tryptophan\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.020\u0026thinsp;\u0026plusmn;\u0026thinsp;0.046***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.783\u0026thinsp;\u0026plusmn;\u0026thinsp;0.023***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.787\u0026thinsp;\u0026plusmn;\u0026thinsp;0.072***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1.940\u0026thinsp;\u0026plusmn;\u0026thinsp;0.135***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCo 30 ppm\u0026thinsp;+\u0026thinsp;combined treatment (citric acid\u0026thinsp;+\u0026thinsp;tryptophan)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eValues are means\u0026thinsp;\u0026plusmn;\u0026thinsp;SD (n\u0026thinsp;=\u0026thinsp;3). *** p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, ** p\u0026thinsp;\u0026lt;\u0026thinsp;0.01, * p\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEffects of cobalt stress and citric acid and tryptophan treatments on oxidative stress indices of \u003cem\u003eSalvia officinalis\u003c/em\u003e.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMDA (nmol/g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTreatments\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.200\u0026thinsp;\u0026plusmn;\u0026thinsp;0.124\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eControl\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.010\u0026thinsp;\u0026plusmn;\u0026thinsp;0.078*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eControl\u0026thinsp;+\u0026thinsp;citric acid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.037\u0026thinsp;\u0026plusmn;\u0026thinsp;0.058*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eControl\u0026thinsp;+\u0026thinsp;tryptophan\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.790\u0026thinsp;\u0026plusmn;\u0026thinsp;0.019***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eControl\u0026thinsp;+\u0026thinsp;combined treatment (citric acid\u0026thinsp;+\u0026thinsp;tryptophan)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.300\u0026thinsp;\u0026plusmn;\u0026thinsp;0.070\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCo 1 ppm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.167\u0026thinsp;\u0026plusmn;\u0026thinsp;0.087\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCo 1 ppm\u0026thinsp;+\u0026thinsp;citric acid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.100\u0026thinsp;\u0026plusmn;\u0026thinsp;0.036*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCo 1 ppm\u0026thinsp;+\u0026thinsp;tryptophan\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.890\u0026thinsp;\u0026plusmn;\u0026thinsp;0.033***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCo 1 ppm\u0026thinsp;+\u0026thinsp;combined treatment (citric acid\u0026thinsp;+\u0026thinsp;tryptophan)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.800\u0026thinsp;\u0026plusmn;\u0026thinsp;0.065***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCo 10 ppm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.583\u0026thinsp;\u0026plusmn;\u0026thinsp;0.082*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCo 10 ppm\u0026thinsp;+\u0026thinsp;citric acid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.433\u0026thinsp;\u0026plusmn;\u0026thinsp;0.034***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCo 10 ppm\u0026thinsp;+\u0026thinsp;tryptophan\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.047\u0026thinsp;\u0026plusmn;\u0026thinsp;0.066***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCo 10 ppm\u0026thinsp;+\u0026thinsp;combined treatment (citric acid\u0026thinsp;+\u0026thinsp;tryptophan)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2.393\u0026thinsp;\u0026plusmn;\u0026thinsp;0.068***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCo 30 ppm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2.183\u0026thinsp;\u0026plusmn;\u0026thinsp;0.072*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCo 30 ppm\u0026thinsp;+\u0026thinsp;citric acid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2.030\u0026thinsp;\u0026plusmn;\u0026thinsp;0.026***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCo 30 ppm\u0026thinsp;+\u0026thinsp;tryptophan\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.470\u0026thinsp;\u0026plusmn;\u0026thinsp;0.000***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCo 30 ppm\u0026thinsp;+\u0026thinsp;combined treatment (citric acid\u0026thinsp;+\u0026thinsp;tryptophan)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eValues are means\u0026thinsp;\u0026plusmn;\u0026thinsp;SD (n\u0026thinsp;=\u0026thinsp;3). *** p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, ** p\u0026thinsp;\u0026lt;\u0026thinsp;0.01, * p\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEffects of cobalt stress and citric acid and tryptophan treatments on antioxidant enzyme activities of \u003cem\u003eSalvia officinalis\u003c/em\u003e.\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=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGPX (U g⁻\u0026sup1; FW)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAPX (U g⁻\u0026sup1; FW)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSOD (U g⁻\u0026sup1; FW)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePOD (U g⁻\u0026sup1; FW)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCAT (U g⁻\u0026sup1; FW)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTreatments\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7.85\u0026thinsp;\u0026plusmn;\u0026thinsp;0.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e9.53\u0026thinsp;\u0026plusmn;\u0026thinsp;0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e24.98\u0026thinsp;\u0026plusmn;\u0026thinsp;0.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e17.69\u0026thinsp;\u0026plusmn;\u0026thinsp;0.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e20.02\u0026thinsp;\u0026plusmn;\u0026thinsp;1.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eControl\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7.76\u0026thinsp;\u0026plusmn;\u0026thinsp;0.42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e9.07\u0026thinsp;\u0026plusmn;\u0026thinsp;0.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e22.37\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e16.61\u0026thinsp;\u0026plusmn;\u0026thinsp;1.08\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e17.68\u0026thinsp;\u0026plusmn;\u0026thinsp;0.90*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eControl\u0026thinsp;+\u0026thinsp;citric acid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6.64\u0026thinsp;\u0026plusmn;\u0026thinsp;0.50*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e7.89\u0026thinsp;\u0026plusmn;\u0026thinsp;0.40**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e21.35\u0026thinsp;\u0026plusmn;\u0026thinsp;0.99***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e14.57\u0026thinsp;\u0026plusmn;\u0026thinsp;0.63***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e17.37\u0026thinsp;\u0026plusmn;\u0026thinsp;0.97*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eControl\u0026thinsp;+\u0026thinsp;tryptophan\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5.38\u0026thinsp;\u0026plusmn;\u0026thinsp;0.83***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e6.51\u0026thinsp;\u0026plusmn;\u0026thinsp;0.57***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e15.68\u0026thinsp;\u0026plusmn;\u0026thinsp;1.15***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e11.52\u0026thinsp;\u0026plusmn;\u0026thinsp;0.56***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e11.61\u0026thinsp;\u0026plusmn;\u0026thinsp;0.99***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eControl\u0026thinsp;+\u0026thinsp;combined treatment (citric acid\u0026thinsp;+\u0026thinsp;tryptophan)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8.74\u0026thinsp;\u0026plusmn;\u0026thinsp;0.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e10.97\u0026thinsp;\u0026plusmn;\u0026thinsp;0.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e27.58\u0026thinsp;\u0026plusmn;\u0026thinsp;0.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e19.75\u0026thinsp;\u0026plusmn;\u0026thinsp;0.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e23.18\u0026thinsp;\u0026plusmn;\u0026thinsp;1.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCo 1 ppm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8.33\u0026thinsp;\u0026plusmn;\u0026thinsp;0.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e10.07\u0026thinsp;\u0026plusmn;\u0026thinsp;0.44**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e25.56\u0026thinsp;\u0026plusmn;\u0026thinsp;0.75**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e18.39\u0026thinsp;\u0026plusmn;\u0026thinsp;0.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e20.69\u0026thinsp;\u0026plusmn;\u0026thinsp;0.69*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCo 1 ppm\u0026thinsp;+\u0026thinsp;citric acid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7.74\u0026thinsp;\u0026plusmn;\u0026thinsp;0.56*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e9.21\u0026thinsp;\u0026plusmn;\u0026thinsp;0.65***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e23.30\u0026thinsp;\u0026plusmn;\u0026thinsp;1.41***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e16.82\u0026thinsp;\u0026plusmn;\u0026thinsp;0.69**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e18.48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.27**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCo 1 ppm\u0026thinsp;+\u0026thinsp;tryptophan\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5.63\u0026thinsp;\u0026plusmn;\u0026thinsp;0.51***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e6.71\u0026thinsp;\u0026plusmn;\u0026thinsp;0.75***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e17.74\u0026thinsp;\u0026plusmn;\u0026thinsp;1.26***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e12.44\u0026thinsp;\u0026plusmn;\u0026thinsp;0.40***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e13.22\u0026thinsp;\u0026plusmn;\u0026thinsp;1.43***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCo 1 ppm\u0026thinsp;+\u0026thinsp;combined treatment (citric acid\u0026thinsp;+\u0026thinsp;tryptophan)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e11.31\u0026thinsp;\u0026plusmn;\u0026thinsp;0.13***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e13.53\u0026thinsp;\u0026plusmn;\u0026thinsp;0.43***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e35.02\u0026thinsp;\u0026plusmn;\u0026thinsp;1.32***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e26.19\u0026thinsp;\u0026plusmn;\u0026thinsp;0.35***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e28.86\u0026thinsp;\u0026plusmn;\u0026thinsp;0.66***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCo 10 ppm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e10.58\u0026thinsp;\u0026plusmn;\u0026thinsp;0.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e12.96\u0026thinsp;\u0026plusmn;\u0026thinsp;0.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e32.35\u0026thinsp;\u0026plusmn;\u0026thinsp;1.24**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e23.27\u0026thinsp;\u0026plusmn;\u0026thinsp;0.42***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e26.38\u0026thinsp;\u0026plusmn;\u0026thinsp;0.46**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCo 10 ppm\u0026thinsp;+\u0026thinsp;citric acid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9.61\u0026thinsp;\u0026plusmn;\u0026thinsp;0.53**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e11.90\u0026thinsp;\u0026plusmn;\u0026thinsp;0.44**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e30.57\u0026thinsp;\u0026plusmn;\u0026thinsp;0.78***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e21.88\u0026thinsp;\u0026plusmn;\u0026thinsp;0.85***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e24.33\u0026thinsp;\u0026plusmn;\u0026thinsp;0.59***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCo 10 ppm\u0026thinsp;+\u0026thinsp;tryptophan\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7.29\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e8.86\u0026thinsp;\u0026plusmn;\u0026thinsp;0.40***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e20.54\u0026thinsp;\u0026plusmn;\u0026thinsp;1.05***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e15.81\u0026thinsp;\u0026plusmn;\u0026thinsp;0.45***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e17.08\u0026thinsp;\u0026plusmn;\u0026thinsp;0.74***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCo 10 ppm\u0026thinsp;+\u0026thinsp;combined treatment (citric acid\u0026thinsp;+\u0026thinsp;tryptophan)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e16.23\u0026thinsp;\u0026plusmn;\u0026thinsp;0.42***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e20.44\u0026thinsp;\u0026plusmn;\u0026thinsp;0.22***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e49.51\u0026thinsp;\u0026plusmn;\u0026thinsp;1.45***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e36.45\u0026thinsp;\u0026plusmn;\u0026thinsp;0.39***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e39.89\u0026thinsp;\u0026plusmn;\u0026thinsp;0.67***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCo 30 ppm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e14.16\u0026thinsp;\u0026plusmn;\u0026thinsp;0.24***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e18.47\u0026thinsp;\u0026plusmn;\u0026thinsp;0.27***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e46.87\u0026thinsp;\u0026plusmn;\u0026thinsp;2.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e33.03\u0026thinsp;\u0026plusmn;\u0026thinsp;0.41***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e35.71\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCo 30 ppm\u0026thinsp;+\u0026thinsp;citric acid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e13.08\u0026thinsp;\u0026plusmn;\u0026thinsp;0.58***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e16.57\u0026thinsp;\u0026plusmn;\u0026thinsp;0.67***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e41.53\u0026thinsp;\u0026plusmn;\u0026thinsp;1.44***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e29.96\u0026thinsp;\u0026plusmn;\u0026thinsp;0.37***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e33.69\u0026thinsp;\u0026plusmn;\u0026thinsp;1.04***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCo 30 ppm\u0026thinsp;+\u0026thinsp;tryptophan\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9.24\u0026thinsp;\u0026plusmn;\u0026thinsp;0.20***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e12.39\u0026thinsp;\u0026plusmn;\u0026thinsp;0.22***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e31.96\u0026thinsp;\u0026plusmn;\u0026thinsp;2.28***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e21.74\u0026thinsp;\u0026plusmn;\u0026thinsp;0.23***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e24.41\u0026thinsp;\u0026plusmn;\u0026thinsp;0.58***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCo 30 ppm\u0026thinsp;+\u0026thinsp;combined treatment (citric acid\u0026thinsp;+\u0026thinsp;tryptophan)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eValues are means\u0026thinsp;\u0026plusmn;\u0026thinsp;SD (n\u0026thinsp;=\u0026thinsp;3). *** p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, ** p\u0026thinsp;\u0026lt;\u0026thinsp;0.01, * p\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEffects of cobalt stress and citric acid and tryptophan treatments on metabolic traits and cobalt accumulation of \u003cem\u003eSalvia officinalis\u003c/em\u003e.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHeavy metal absorption(mg g⁻\u0026sup1;)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(\u0026micro;mol g⁻\u0026sup1;) Proline\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(mg g⁻\u0026sup1;) Oxalate\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e(mg g⁻\u0026sup1;) Malate\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTotal amino acids(mg g⁻\u0026sup1;)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e(mg g⁻\u0026sup1;) Protein\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003e(mg g⁻\u0026sup1;) Sugar\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eTreatments\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.52\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.43\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.59\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.68\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e1.87\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e2.48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e3.60\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eControl\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.49\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.56\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.64\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.76\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e1.88\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e2.68\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e3.79\u0026thinsp;\u0026plusmn;\u0026thinsp;0.20*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eControl\u0026thinsp;+\u0026thinsp;citric acid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.52\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.80\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.73\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.84\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e2.13\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e2.94\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e4.21\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eControl\u0026thinsp;+\u0026thinsp;tryptophan\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e2.41\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e1.00\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1.13\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e2.91\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e4.08\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e5.79\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eControl\u0026thinsp;+\u0026thinsp;combined treatment (citric acid\u0026thinsp;+\u0026thinsp;tryptophan)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.53\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.65\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e1.61\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e2.28\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e3.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCo 1 ppm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.54\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.59\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.70\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e1.68\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e2.40\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e3.54\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCo 1 ppm\u0026thinsp;+\u0026thinsp;citric acid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.47\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.64\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.63\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.77\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e1.94\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e2.65\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e3.89\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCo 1 ppm\u0026thinsp;+\u0026thinsp;tryptophan\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.49\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e2.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.13***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.89\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.99\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e2.63\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e3.80\u0026thinsp;\u0026plusmn;\u0026thinsp;0.16***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e5.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCo 1 ppm\u0026thinsp;+\u0026thinsp;combined treatment (citric acid\u0026thinsp;+\u0026thinsp;tryptophan)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.40\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.96\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.51\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e1.28\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e1.64\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e2.54\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCo 10 ppm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.36\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.13\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.53\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e1.31\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e1.90\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e2.70\u0026thinsp;\u0026plusmn;\u0026thinsp;0.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCo 10 ppm\u0026thinsp;+\u0026thinsp;citric acid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.38\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.28\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.52\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.61\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e1.55\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e2.03\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e2.79\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCo 10 ppm\u0026thinsp;+\u0026thinsp;tryptophan\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.35\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.73\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.68\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.80\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e2.06\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e2.76\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e3.97\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCo 10 ppm\u0026thinsp;+\u0026thinsp;combined treatment (citric acid\u0026thinsp;+\u0026thinsp;tryptophan)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.23\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.69\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.32\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.36\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e0.98\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e1.33\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e1.79\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCo 30 ppm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.23\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.88\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.30\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.38\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e0.97\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e1.36\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e1.87\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCo 30 ppm\u0026thinsp;+\u0026thinsp;citric acid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.21\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.94\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.34\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.44\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e1.17\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e1.48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e2.23\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCo 30 ppm\u0026thinsp;+\u0026thinsp;tryptophan\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.25\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.24\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.49\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.58\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e1.39\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e2.03\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e2.90\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCo 30 ppm\u0026thinsp;+\u0026thinsp;combined treatment (citric acid\u0026thinsp;+\u0026thinsp;tryptophan)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eValues are means\u0026thinsp;\u0026plusmn;\u0026thinsp;SD (n\u0026thinsp;=\u0026thinsp;3). *** p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, ** p\u0026thinsp;\u0026lt;\u0026thinsp;0.01, * p\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003c/div\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"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":"environmental-science-and-pollution-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"espr","sideBox":"Learn more about [Environmental Science and Pollution Research](https://www.springer.com/journal/11356)","snPcode":"11356","submissionUrl":"https://submission.nature.com/new-submission/11356/3","title":"Environmental Science and Pollution Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Salvia officinalis, cobalt stress, biostimulants, oxidative stress, antioxidant defense","lastPublishedDoi":"10.21203/rs.3.rs-9167832/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9167832/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe accumulation of cobalt (Co) in agricultural systems poses a serious threat to plant productivity, particularly in high-value medicinal species. This study evaluated the potential of exogenous citric acid (CA) and tryptophan (Trp), applied individually or in combination, to mitigate Co-induced phytotoxicity in hydroponically grown \u003cem\u003eSalvia officinalis\u003c/em\u003e L. Plants were exposed to four Co concentrations (0, 1, 10, and 30 ppm) and four biostimulant treatments (control, 2 mM CA, 2 mM Trp, and CA\u0026thinsp;+\u0026thinsp;Trp) for four weeks. Increasing Co levels, especially 10 and 30 ppm, markedly impaired plant growth, biomass accumulation, and photosynthetic pigment contents (chlorophyll a, chlorophyll b, carotenoids, β-carotene, and anthocyanins). These effects were accompanied by enhanced lipid peroxidation, increased activities of antioxidant enzymes (CAT, POD, SOD, APX, and GPX), and significant disruption of primary metabolism, including reductions in soluble sugars, proteins, amino acids, malate, and oxalate. Application of CA or Trp alone partially alleviated Co toxicity; however, their combined application exerted a pronounced synergistic effect, resulting in substantial recovery of growth performance, photosynthetic capacity, and metabolic balance. Moreover, the combined treatment significantly reduced oxidative damage and moderated antioxidant enzyme activities, reflecting a lower oxidative burden, and limited Co accumulation in plant tissues. These findings suggest that CA may reduce Co bioavailability through chelation, while Trp likely enhances internal metabolic and antioxidative capacity. Their synergistic use represents an effective and sustainable biostimulant strategy to improve cobalt tolerance and ensure the safe production of medicinal plants under heavy metal stress in hydroponic systems.\u003c/p\u003e","manuscriptTitle":"Interactive effects of citric acid and tryptophan on cobalt bioavailability and oxidative stress responses in Salvia officinalis under controlled contamination conditions","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-23 01:02:30","doi":"10.21203/rs.3.rs-9167832/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major Revision","date":"2026-05-07T08:12:32+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2026-04-15T01:23:49+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-15T01:09:05+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Environmental Science and Pollution Research","date":"2026-04-14T13:43:03+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-13T04:52:29+00:00","index":"","fulltext":""},{"type":"submitted","content":"Environmental Science and Pollution Research","date":"2026-04-08T03:44:19+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"environmental-science-and-pollution-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"espr","sideBox":"Learn more about [Environmental Science and Pollution Research](https://www.springer.com/journal/11356)","snPcode":"11356","submissionUrl":"https://submission.nature.com/new-submission/11356/3","title":"Environmental Science and Pollution Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"5593209e-6019-4263-bff0-c2d0f1507166","owner":[],"postedDate":"April 23rd, 2026","published":true,"recentEditorialEvents":[{"type":"decision","content":"Major Revision","date":"2026-05-07T08:12:32+00:00","index":"","fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"in-revision","subjectAreas":[],"tags":[],"updatedAt":"2026-05-07T13:21:16+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-23 01:02:30","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9167832","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9167832","identity":"rs-9167832","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}