Dehydroascorbate Reductase Activity Research Articles

Tert-Butylhydroquinone alleviates a postharvest pericarp browning of longan fruit by regulating antioxidant metabolism.

Harvested longan fruit is prone to pericarp browning, which restricts preservation quality and shortens fruit shelf life. The antioxidant system can defend against oxidative stress-mediated quality deterioration such as fruit browning. This study aimed to evaluate the effect of tert-butylhydroquinone (TBHQ) on anti-browning ability of longan fruit in association with redox metabolism. The results indicated that the application of 0.02% TBHQ significantly suppressed the progression of pericarp browning. In comparison with control, TBHQ treatment decreased the contents of hydrogen peroxide (H2O2), superoxide radical (O2 -⋅), and malondialdehyde, and retained high levels of ascorbic acid (AsA), glutathione (GSH), total phenolics as well as 1,1-diphenyl-2-picrylhydrazyl scavenging rate. Enhanced enzymatic activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase, and dehydroascorbate reductase (DHAR), but decreased activities of polyphenol oxidase and peroxidase were also observed in TBHQ-treated fruit. Gene expression analysis indicated that redox metabolism-related genes, including DlSOD, DlCAT, DlGR, and DlAPX, were upregulated after TBHQ treatment. Correlation analysis suggested that antioxidants, including AsA, GSH, CAT, APX, SOD, and DHAR, were negatively correlated to reactive oxygen species production and percarp browning. These results suggest that TBHQ is effective in alleviating pericarp browning by increasing antioxidant capacity of longan fruit.

Ethylene and hydrogen sulfide regulate hexavalent chromium toxicity in two pulse crops: Implication on growth, photosynthetic activity, oxidative stress and ascorbate glutathione cycle

Sustainable agriculture has become prime importance to feed growing population. To achieve this goal application of exogenous hormones and signaling molecules are gaining important. In this context, we have investigated potential of ethylene (25 μM ethephon; donor) and H2S (10 μM NaHS; donor) in mitigating hexavalent chromium [Cr (VI), 50 μM] toxicity in two pulse seedlings: black bean and mung bean. Cr(VI) declined growth and gas exchange parameters (photosynthetic rate, stomatal conductance, sub cellular CO2 concentration, and transpiration level) which was accompanied by intracellular accumulation of Cr in both pulse crops and the damaging effect was greater in mung bean seedlings. The suppression in the growth and related parameters was occurred due to higher buildup of oxidative stress markers; O2•‾, H2O2, lipid peroxidation (as malondialdehyde, MDA equivalents) and membrane injury in leaf and root of both pulse crops. Cr induced disturbance in AsA-GSH cycle (reduction in the activity of glutathione reductase, ascorbate peroxidase, monodehydroascorbate reductase and dehydroascorbate reductase, and the amount of ASA and GSH) could be one of the reasons for greater accumulation of H2O2. Further, exogenous application of ethylene and H2S significantly ameliorated Cr toxicity on growth and photosynthetic activity by significantly lowering the intracellular Cr accumulation and oxidative biomarkers, and also by strengthening the activity of AsA-GSH cycle. The exogenous application of biosynthesis inhibitors of ethylene (AVG) and H2S (PAG) caused greater damaging effect on these parameters due to more accumulation of Cr(VI), thereby suggesting that the endogenous levels of these regulators are critical for Cr(VI) tolerance. Interestingly, ET did not rescue adverse effects of Cr(VI) in absence of endogenous H2S, while H2S could do so even without endogenous ethylene, suggesting that H2S played downstream signaling to ethylene in regulating Cr(VI) toxicity. Hence, being cheap and easily available theses growth regulators may be considered for sustainable agriculture.

The role of ascorbate redox turnover in iron toxicity tolerance

Iron (Fe) toxicity is a major abiotic stress in lowland rice production. Breeding tolerant varieties has proven challenging due to the complex genetic architecture of Fe toxicity tolerance and the strong genotype-by-environment interactions. Additionally, conventional methods for phenotyping visible stress symptoms are often inaccurate, inconsistent, and lack reproducibility.In our previous work, we identified that ascorbate redox regulation, mediated by the activities of dehydroascorbate reductase (DHAR) and ascorbate oxidase (AO), contributed to high tolerance in an indica rice genotype across various environments. To explore whether this mechanism is common among other rice genotypes, we selected ten genotypes with contrasting stress symptoms under Fe-toxic conditions to examine the roles of DHAR and AO in regulating Fe toxicity tolerance. Additionally, we aimed to develop objective and accurate image-based phenotyping methods to replace the traditional leaf bronzing scoring method.Among the ten genotypes we tested, we found significant positive correlations between DHAR activity and stress symptoms in plants grown under both Fe toxicity and control conditions, suggesting a general link between ascorbate redox regulation and Fe toxicity tolerance. Using RGB signals from leaf images of plants exposed to 1000 mg/L Fe2+, we evaluated 36 different color indices to quantify stress symptoms. We identified the normalized green‒red difference index as most significant in quantifying stress symptoms under Fe toxicity conditions.Our findings suggest that DHAR activity could be potentially employed as a biomarker in the screening of rice germplasms and breeding tolerant cultivars to Fe toxicity.

Maintaining quality of postharvest green pepper fruit using melatonin by regulating membrane lipid metabolism and enhancing antioxidant capacity

Green pepper quality often deteriorates during storage because of membrane lipid damage and oxidative stress. This study investigated the effects of exogenous melatonin (MT) on green pepper storage quality, membrane lipids, and antioxidant metabolism. The results showed that MT increased the activities of superoxide dismutase, catalase, ascorbate peroxidase, peroxidase, monodehydroascorbate reductase, and dehydroascorbate reductase in green peppers compared to the control group. It upregulated expression of multiple enzymes; reduced accumulation of reactive oxygen species such as dehydroascorbic acid, H2O2, and O2.-; and maintained high ascorbic acid, glutathione, coenzyme II, and nicotinamide adenine dinucleotide while reducing oxidized glutathione levels. In addition, MT decreased lipoxygenase and phospholipase D activities, downregulated ReLOX and RePLD expression, and delayed the degradation of phosphatidylcholine, phosphatidylethanolamine, and oleic, linoleic, and linolenic acids in green peppers. These results suggest that MT helps to improve the chilling injury and quality of green peppers and extends shelf life.

Continuous Blue Light Treatment Enhances the Nutritional Value of Hydroponically Grown Eruca vesicaria L. by Improving Ascorbic Acid Biosynthesis.

This study investigates the effect of continuous blue light (CBL) treatment on quality-related metabolites, focusing on ascorbic acid (AsA) accumulation in hydroponically grown Eruca vesicaria (L.). Plants were subjected to CBL treatment, consisting of 24-h exposure to constant-intensity blue light (48 μmol m-2 s-1) and 12-h exposure to the remaining spectrum (192 μmol m-2 s-1). The activities of key enzymes in AsA biosynthesis and recycling were analyzed, including L-galactono-1,4-lactone dehydrogenase (GalLDh), monodehydroascorbate reductase (MDhAR), dehydroascorbate reductase (DhAR), and ascorbate peroxidase (APX). The results showed a significant increase in AsA accumulation of 65.9% during the "day" and 69.1% during the "night" phases under CBL compared to controls. GalLDh activity increased by 20% during the "day phase" in CBL-treated plants. APX activity also rose significantly under CBL conditions, by 101% during the "day" and 75.6% during the "night". However, this did not affect dehydroascorbic acid levels or the activities of MDhAR and DhAR. These findings highlight the potential of tailored light treatments to enhance the nutraceutical content of horticultural species, offering valuable insights for sustainably improving food quality in controlled-environment agriculture (CEA) systems and understanding the roles of blue light in ascorbic acid biosynthesis.

Short‐Term Soil Waterlogging Improves Cotton Tolerance to High Temperature by Triggering Antioxidant Defence System in Cotton Seedlings

ABSTRACTSoil waterlogging and high temperature (HT) are serious abiotic stresses that negatively affect cotton growth and yield. Yet effects of prewaterlogging to HT subsequently in cotton seedlings have not been obtained. To address this, two temperature conditions (30/20°C and 35/25°C) and two soil waterlogging levels (0 and 3 days) were established during the cotton seedling stage. Results showed that indexes of plant performance were decreased markedly under HT. Unexpectedly, plant performance for the treatment of HT combined with 3 days of soil waterlogging (HW) was better than HT treatment (specifically, increase of 7.9%, 9.0%, 10.2%, 5.4% and 4.6% in leaf area, plant height, belowground biomass, aboveground biomass and root‐to‐shoot ratio was detected). Decreases in MDA (malondialdehyde), H2O2 (hydrogen peroxide) contents and (superoxide radicals) generation rate under HW treatment were observed by 14.1%, 7.7% and 14.1%, respectively, compared with HT. Moreover, ASA (ascorbic acid) content and DHAR (dehydroascorbate reductase) activity were improved by 19.7% and 13.8% for HW treatment relative to HT, however, the opposite situation for activities of APX (ascorbate peroxidase) and GR (glutathione reductase). Besides, activities of SOD (superoxide dismutase), CAT (catalase) and POD (peroxidase) in HW treatment were increased by 16.7%, 8.3% and 18.4%, separately. Thus, we concluded that short‐term soil waterlogging improved cotton cross‐tolerance to the continued high‐HT stress by enhanced SOD, CAT, POD and DHAR activities, increased ASA content in cotton seedlings. These results were expected to provide a theoretical basis for understanding cotton's cross‐tolerance to abiotic stress.

Metabolic and Functional Interactions of H2S and Sucrose in Maize Thermotolerance through Redox Homeodynamics.

Hydrogen sulfide (H2S) is a novel gasotransmitter. Sucrose (SUC) is a source of cellular energy and a signaling molecule. Maize is the third most common food crop worldwide. However, the interaction of H2S and SUC in maize thermotolerance is not widely known. In this study, using maize seedlings as materials, the metabolic and functional interactions of H2S and SUC in maize thermotolerance were investigated. The data show that under heat stress, the survival rate and tissue viability were increased by exogenous SUC, while the malondialdehyde content and electrolyte leakage were reduced by SUC, indicating SUC could increase maize thermotolerance. Also, SUC-promoted thermotolerance was enhanced by H2S, while separately weakened by an inhibitor (propargylglycine) and a scavenger (hypotaurine) of H2S and a SUC-transport inhibitor (N-ethylmaleimide), suggesting the interaction of H2S and SUC in the development of maize thermotolerance. To establish the underlying mechanism of H2S-SUC interaction-promoted thermotolerance, redox parameters in mesocotyls of maize seedlings were measured before and after heat stress. The data indicate that the activity and gene expression of H2S-metabolizing enzymes were up-regulated by SUC, whereas H2S had no significant effect on the activity and gene expression of SUC-metabolizing enzymes. In addition, the activity and gene expression of catalase, glutathione reductase, ascorbate peroxidase, peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase, and superoxide dismutase were reinforced by H2S, SUC, and their combination under non-heat and heat conditions to varying degrees. Similarly, the content of ascorbic acid, flavone, carotenoid, and polyphenol was increased by H2S, SUC, and their combination, whereas the production of superoxide radicals and the hydrogen peroxide level were impaired by these treatments to different extents. These results imply that the metabolic and functional interactions of H2S and sucrose signaling exist in the formation of maize thermotolerance through redox homeodynamics. This finding lays the theoretical basis for developing climate-resistant maize crops and improving food security.

Physiological and multi-omics analysis reveals the influence of copper on Halophila beccarii Asch

High concentrations of copper can pollute coastal waters, primarily from agricultural runoff and mining activities, which can harm marine organisms, including seagrasses. The molecular mechanism of copper toxicity to seagrass currently remains unclear. To determine the response to copper, physiological and multi-omic analyses were conducted to explore the molecular mechanism by which copper affects the global threatened seagrass Halophila beccarii Asch. Excessive copper stress causes oxidative damage and stimulates the activity of the antioxidant enzyme system to remove excess reactive oxygen species (ROS), thereby reducing the damage caused by copper stress. Cu increases the activities of superoxide dismutase (EC 1.15.1.1), catalase (EC 1.11.1.6), peroxidase (EC 1.11.1.7), ascorbate peroxidase (EC 1.11.1.11), glutathione peroxidase (EC 1.11.1.9), ascorbate oxidase (EC 1.10.3.3), glutathione reductase (EC 1.6.4.2), and dehydroascorbate reductase (EC 1.8.5.1) and the content of malondialdehyde and reduces the activity of monodehydroascorbate reductase (EC 1.6.5.4). Under copper stress, H. beccarii upregulates the metabolic pathways of steroid biosynthesis and cutin, suberin, and wax biosynthesis, downregulates the metabolic pathways of arginine and proline metabolism and fructose and mannose metabolism; the levels of expression of the ribosome-related genes; upregulates the levels of expression of circadian rhythm-related proteins and downregulates the levels of glutathione metabolism and the proteins related to carbon fixation. This study provides new insights into the response of seagrass to copper stress and reports potential candidate metabolites, genes, and proteins that can be considered as biomarkers to improve the protection and management of seagrass meadows.

The Role of Glutathione Transferase Omega-Class Variant Alleles in Individual Susceptibility to Ovarian Cancer.

The tumor microenvironment is affected by reactive oxygen species and has been suggested to have an important role in ovarian cancer (OC) tumorigenesis. The role of glutathione transferases (GSTs) in the maintenance of redox balance is considered as an important contributing factor in cancer, including OC. Furthermore, GSTs are mostly encoded by highly polymorphic genes, which further highlights their potential role in OC, known to originate from accumulated genetic changes. Since the potential relevance of genetic variations in omega-class GSTs (GSTO1 and GSTO2), with somewhat different activities such as thioltransferase and dehydroascorbate reductase activity, has not been clarified as yet in terms of susceptibility to OC, we aimed to investigate whether the presence of different GSTO1 and GSTO2 genetic variants, individually or combined, might represent determinants of risk for OC development. Genotyping was performed in 110 OC patients and 129 matched controls using a PCR-based assay for genotyping single nucleotide polymorphisms. The results of our study show that homozygous carriers of the GSTO2 variant G allele are at an increased risk of OC development in comparison to the carriers of the referent genotype (OR1 = 2.16, 95% CI: 0.88-5.26, p = 0.08; OR2 = 2.49, 95% CI: 0.93-6.61, p = 0.06). Furthermore, individuals with GST omega haplotype H2, meaning the concomitant presence of the GSTO1*A and GSTO2*G alleles, are more susceptible to OC development, while carriers of the H4 (*A*A) haplotype exhibited lower risk of OC when crude and adjusted haplotype analysis was performed (OR1 = 0.29; 95% CI: 0.12-0.70; p = 0.007 and OR2 = 0.27; 95% CI: 0.11-0.67; p = 0.0054). Overall, our results suggest that GSTO locus variants may confer OC risk.

Arbuscular mycorrhizal fungi enhanced resistance to low-temperature weak-light stress in snapdragon (Antirrhinum majus L.) through physiological and transcriptomic responses.

Low temperature (LT) and weak light (WL) seriously affects the yield and quality of snapdragon in winter greenhouse. Arbuscular mycorrhizal fungi (AMF) exert positive role in regulating growth and enhancing abiotic stress tolerance in plants. Nevertheless, the molecular mechanisms by AMF improve the LT combined with WL (LTWL) tolerance in snapdragon remain mostly unknown. We compared the differences in root configuration, osmoregulatory substances, enzymatic and non-enzymatic antioxidant enzyme defense systems and transcriptome between AMF-inoculated and control groups under LT, WL, low light, and LTWL conditions. Our analysis showed that inoculation with AMF effectively alleviated the inhibition caused by LTWL stress on snapdragon root development, and significantly enhanced the contents of soluble sugars, soluble proteins, proline, thereby maintaining the osmotic adjustment of snapdragon. In addition, AMF alleviated reactive oxygen species damage by elevating the contents of AsA, and GSH, and the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR), and glutathione reductase (GR). RNA-seq analysis revealed that AMF regulated the expression of genes related to photosynthesis (photosystem I related proteins, photosystem II related proteins, chlorophyll a/b binding protein), active oxygen metabolism (POD, Fe-SOD, and iron/ascorbate family oxidoreductase), plant hormone synthesis (ARF5 and ARF16) and stress-related transcription factors gene (bHLH112, WRKY72, MYB86, WRKY53, WRKY6, and WRKY26) under LTWL stress. We concluded that mycorrhizal snapdragon promotes root development and LTWL tolerance by accumulation of osmoregulatory substances, activation of enzymatic and non-enzymatic antioxidant defense systems, and induction expression of transcription factor genes and auxin synthesis related genes. This study provides a theoretical basis for AMF in promoting the production of greenhouse plants in winter.

Effects of Nano-Silica and Multi-Walled Carbon Nanotubes on Grape Seedlings under Salt Stress

To improve the salt tolerance of grape seeds and seedlings under salt stress, this study was conducted including two control groups (CK, S) and five experimental groups (S + Si40, S + Si60, S + Si80, S + C90, S + Si40 + C90), and the physiological characteristics of grape seed germination and seedlings were studied using 40, 60, and 80 μg/mL of nano-silica treatments and by mixing 40 μg/mL of nano-silica with 90 μg/mL of multi-walled carbon nanotubes (MWCNTs), respectively. The combined treatment of 40 μg/mL nano-silica and 90 μg/mL MWCNTs resulted in the best rate of growth in grape seeds and root length and an increased germination rate when compared with the other concentrations. The combined treatment reduced the MDA content in the grape seedling leaves and increased the activities of superoxide (SOD), peroxidase (POD), catalase (CAT), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR), ascorbate peroxidase (APX), glutathione-s-transferase (GT), and glutathione reductase (GR). In addition, the scavenging activity of DPPH· was also maintained by the combined treatment. In conclusion, a combined treatment with 40 μg/mL nano-silica and 90 μg/mL MWCNTs significantly increased the reduction capacity through the direct and indirect antioxidant systems (AsA-GSH cycle) and maintained a high antioxidant capacity of grape seedlings under salt stress.

Involvement of GLR-mediated nitric oxide effects on ROS metabolism in Arabidopsis plants under salt stress

Plant glutamate receptor-like channels (GLRs) play important roles in plant development, immune response, defense signaling and Nitric oxide (NO) production. However, their involvement in abiotic stress responses, particularly in regulating Reactive Oxygen Species (ROS), is not well understood. This study aimed to investigate GLR-mediated NO production on ROS regulation in salt-stressed cells. To achieve this, Arabidopsis thaliana Columbia (Col-0) were treated with NaCl, glutamate antagonists [(DNQX (6,7-dinitroquinoxaline-2,3-dione and AP-5(D-2-amino-5-phosphono pentanoic acid)], and NO scavenger [cPTIO (2-(4-Carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt)]. Salt-stressed plants in combination with DNQX and AP-5 have exhibited higher increase in lipid peroxidation (TBARS), hydrogen peroxide (H2O2) and superoxide radical (O−2) contents as compared to solely NaCl-treated plants. Furthermore, NO and total glutathione contents, and S-nitrosoglutathione reductase (GSNOR) activity decreased with these treatments. AP-5 and DNQX increased the activities of NADPH oxidase (NOX), catalase (CAT), peroxidase (POX), cell wall peroxidase (CWPOX) in salt-stressed Arabidopsis leaves. However, their activities (except NOX) were significantly inhibited by cPTIO. Conversely, the combination of NaCl and GLR antagonists, NO scavenger decreased the activities of ascorbate peroxidase (APX), superoxide dismutase (SOD), glutathione reductase (GR), dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDHAR) resulting in elevated GSSG levels, a low GSH/GSSG ratio, impaired ROS scavenging, excessive ROS accumulation and cell membrane damage. The findings of this study provide evidence that GLR-mediated NO plays a crucial role in improvement of the tolerance of Arabidopsis plants to salt-induced oxidative stress. It helps to maintain cellular redox homeostasis by reducing ROS accumulation and increasing the activity of SOD, GSNOR, and the ASC-GSH cycle enzymes.

Ascorbate-glutathione cycle in wheat and rice seedlings under anoxia and subsequent reaeration.

The most important part of the plant antioxidant system is the ascorbate-glutathione cycle (AGC), the activity of which is observed upon exposure to a range of stressors, including lack of O2, and oxidative stress occurring immediately after the restoration of oxygen access, hereafter termed reaeration or post-anoxia. The operation of the AGC (enzymes and low-molecular components) in wheat (Triticum aestivum, cv. Leningradka, non-resistant to hypoxia) and rice (Oryza sativa, cv. Liman, resistant) seedlings after 24 h anoxia and 1 h or 24 h reaeration was studied. Significant accumulation of oxidized forms of ascorbate and glutathione was revealed in the non-resistant plant (wheat) after 24 h of anoxia and reaeration, indicating the development of oxidative stress. In the resistant plant (rice), reduced forms of these antioxidants prevailed both in normoxia and under stress, which may indicate their intensive reduction. In wheat, the activities of ascorbate peroxidase and dehydroascorbate reductase in shoots, and monodehydroascorbate reductase and glutathione reductase in roots decreased under anoxia and reaeration. The activity of antioxidant enzymes was maintained in rice under lack of oxygen (ascorbate peroxidase, glutathione reductase) and increased during post-anoxia (AGC reductases). Anoxia stimulated accumulation of mRNA of the organellar ascorbate peroxidase genes OsAPX3, OsAPX5 in shoots, and OsAPX3-5 and OsAPX7 in roots. At post-anoxia, the contribution of the OsAPX1 and OsAPX2 genes encoding the cytosolic forms of the enzyme increased in the whole plant, and so did that of the OsAPX8 gene for the plastid form of the enzyme. The accumulation of mRNA of the genes OsMDAR2 and OsMDAR4 encoding peroxisomal and cytosolic monodehydroascorbate reductase as well as the OsGR2 and OsGR3 for cytosolic and organellar glutathione reductase was activated during reaeration in shoots and roots. In most cases, O2 deficiency activated the genes encoding the peroxisomal, plastid, and mitochondrial forms of the enzymes, and upon reaeration, an enhanced activity of the genes encoding the cytoplasmic forms was observed. Taken together, the inactivation of AGC enzymes was revealed in wheat seedlings during anoxia and subsequent reaeration, which disrupted the effective operation of the cycle and triggered the accumulation of oxidized forms of ascorbate and glutathione. In rice, anoxia led to the maintenance of the activity of AGC enzymes, and reaeration stimulated it, including at the level of gene expression, which ensured the effective operation of AGC.

Drought priming reduces Calligonum mongolicum sensitivity to recurrent droughts via coordinated regulation of osmolytes, antioxidants, and hormones.

Pre-exposure of plants to abiotic stressors may induce stress memory and improve tolerance to subsequent stresses. Here, 3-month-old Calligonum mongolicum seedlings were exposed to drought (60 days) with (primed) or without (unprimed) early drought exposure of 50 days, to determine whether this enhances seedling resistance and investigate possible underlying mechanisms. Compared to unprimed, primed seedlings had higher biomass, shoot relative water content (15% and 22%), chlorophyll a, chlorophyll b, and carotenoids. They also had more superoxide anions (O2 -• ) and H2 O2 scavenging mechanisms through higher activity of SOD, CAT, APX, and dehydroascorbate reductase in assimilating shoots and roots, resulting in less ROS and oxidative stress damage. Plants also had higher ABA and JA but lower SA, likely reflecting an adaptive response to subsequent stress. Primed seedlings accumulated more IAA and brassinosteroids, which may account for their better growth. Accumulation of glycine betaine, pro, and total amino acids in assimilating shoots and roots of primed seedlings led to reduced osmotic stress. Drivers of responses of non-primed and primed seedlings to drought varied. Responses of primed seedlings were primarily characterized by more photosynthetic pigments, increased oxidative scavenging of O2 -• and H2 O2 , more phytohormones and osmolytes. Early drought priming of drought stress memory in C. mongolicum seedlings may provide a useful management approach to improve seedling establishment in vegetation restoration programs.

Ascorbate‐glutathione cycle alleviates low‐temperature‐induced oxidative stress for augmented growth of Nannochloropsis oceanica Rose Bengal mutants

AbstractStudying the adaptive mechanisms of algae to abiotic stresses, such as low temperature and high light intensities, can help facilitate large‐scale outdoor production. Consequently, the role played by the antioxidant defense system in the tolerance of Nannochloropsis oceanica Rose Bengal (RB) mutants, with a truncated PSII complex, to low‐temperature (LT, 18°C) under high‐light (HL, 250 μmol⋅m−2⋅s−1) conditions was explored. The wild type (WT) exhibited O2•‐ and H2O2 accumulation, lipid peroxidation, and cell death upon LT treatment, which was exacerbated by LT‐HL. The RB mutants showed no oxidative stress during LT or LT‐HL. Ascorbate peroxidase (APX; EC 1.11.1.11), dehydroascorbate reductase (DHAR; EC 1.8.5.1), and glutathione reductase (GR; E.C. 1.6.4.2) activity and transcript abundance increased by LT and LT‐HL conditions in the RB mutants but not in the WT. In the RB mutants, the ascorbate (AsA) pool size stayed low, but the AsA/DHA ratio increased under LT and LT‐HT conditions, while the glutathione (GSH) pool size and GSH/GSSG ratio increased. The RB mutants treated with buthionine sulfoximine (BSO), an inhibitor of GSH biosynthesis, became susceptible to LT‐HL stress. The expression of GLUTAMYLCYSTEINE SYNTHETASE (NoGSH1) and GLUTATHIONE SYNTHASE (NoGSH2A and NoGSH2B), responsible for GSH biosynthesis, was upregulated in two RB mutants by LT and LT‐HL stress, while that of GULONOLACTONE OXIDASE (NoGulo), involved in AsA biosynthesis, remained constant. Beyond reduced light energy absorption, increased the Ascorbate‐Glutathione cycle enzyme expression and AsA and GSH regeneration in Nannochloropsis RB mutants enable adaptations to prevent oxidative damage caused by high‐intensity illumination at low temperatures.

Graphene oxide-based aerogel stimulates growth, mercury accumulation, photosynthesis-related gene expression, antioxidant efficiency and redox status in wheat under mercury exposure

Mercury (Hg) pollution is a global concern in cropland systems. Hg contamination causes a disruption in the growth, energy metabolism, redox balance, and photosynthetic activity of plants. In the removal of Hg toxicity, a recent critical strategy is the use of aerogels with biodegradability and biocompatibility. However, it is unknown how graphene oxide-based aerogels stimulate the defense systems in wheat plants exposed to Hg toxicity. Therefore, in this study, the photosynthetic, genetic, and biochemical effects of reduced graphene oxide aerogel treatments (gA; 50-100-250 mg L−1) were examined in wheat (Triticum aestivum) under Hg stress (50 μM HgCl2). The relative growth rate (RGR) significantly decreased (84%) in response to Hg stress. However, the reduced RGR and water relations (RWC) of wheat were improved by gA treatments. The impaired gas exchange levels (stomatal conductance, carbon assimilation rate, intercellular CO2 concentrations, and transpiration rate) caused by stress were reversed under Hg plus gAs. Additionally, stress hampered chlorophyll fluorescence (Fv/Fo, Fv/Fm), and under Hg toxicity the expression of psaA genes was reduced (>0.4-fold), but psaB gene was significantly up-regulated (>3-fold) which are the genes involved in PSI. By increasing expression patterns of both genes relating to PSI, gAs reversed the adverse consequences on Fv/Fo and Fv/Fm in the presence of excessive Hg concentration. The activities of glutathione S-transferase (GST), glutathione reductase (GR), catalase (CAT), ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR) decreased under Hg toxicity. On the other hand, the activities of superoxide dismutase (SOD), APX, GST, and glutathione peroxidase (GPX) increased following gA treatments against stress, leading to the successful elimination of toxic levels of H2O2 and lipid peroxidation (TBARS content) by decreasing the levels by about 30%, and 40%, respectively. By modulating enzyme/non-enzyme activity/contents including the AsA-GSH cycle, gAs contributed to the protection of the cellular redox state. Most important of all, gA applications were able to reduce Hg intake by approximately 66%. Therefore, these results showed that gAs were effective in highly inhibiting Hg uptake and could significantly increase wheat tolerance to toxicity by eliminating Hg-induced oxidative damage and inhibiting metabolic processes involved in photosynthesis. The findings obtained from the study provide a new perspective on the alleviation roles of reduced graphene oxide aerogels as an effective adsorbent for decreasing damages of mercury toxicity in wheat plants.

The role of salicylic acid on glutathione metabolism under endoplasmic reticulum stress in tomato

The endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) are highly dependent on phytohormones such as salicylic acid (SA). In this study, the effect of SA supplementation and the lack of endogenous SA on glutathione metabolism were investigated under ER stress in wild-type (WT) and transgenic SA-deficient NahG tomato (Solanum lycopersicum L.) plants. The expression of the UPR marker gene SlBiP was dependent on SA levels and remained lower in NahG plants. Exogenous application of the chemical chaperone 4-phenylbutyrate (PBA) also reduced tunicamycin (Tm)-induced SlBiP transcript accumulation. At the same time, Tm-induced superoxide and hydrogen peroxide production were independent of SA, whereas the accumulation of reduced form of glutathione (GSH) and the oxidised glutathione (GSSG) was regulated by SA. Tm increased the activity of glutathione reductase (GR; EC 1.6.4.2) independently of SA, but the activities of dehydroascorbate reductase (DHAR; EC 1.8.5.1) and glutathione S-transferases (GSTs; EC 2.5.1.18) were increased by Tm in a SA-dependent manner. SlGR2, SlGGT and SlGSTT2 expression was activated in a SA-dependent way upon Tm. Although expression of SlGSH1, SlGSTF2, SlGSTU5 and SlGTT3 did not change upon Tm treatment in leaves, SlGR1 and SlDHAR2 transcription decreased. PBA significantly increased the expression of SlGR1, SlGR2, SlGSTT2, and SlGSTT3, which contributed to the amelioration of Tm-induced ER stress based on the changes in lipid peroxidation and cell viability. Malondialdehyde accumulation and electrolyte leakage were significantly higher in WT as compared to NahG tomato leaves under ER stress, further confirming the key role of SA in this process.

Sucrose and brassinolide alleviated nitrite accumulation, oxidative stress and the reduction of phytochemicals in kale sprouts stored at low temperature

Browning, nitrite accumulation, oxidative stress, and loss of nutrients in postharvest sprout during low-temperature storage are important issues that affect storage quality of sprouts. This study evaluated the effects of sucrose, brassinolide (BR), and their combination on the growth and development of fresh kale sprouts, and reactive oxygen metabolism, ascorbate-glutathione (AsA-GSH) cycle, browning, nitrite content, and bioactive ingredients of kale sprouts stored at low temperature, in order to improve the physiological traits of postharvest sprouts, resist the oxidative stress in sprouts during low-temperature storage and inhibit the loss of plant nutrients. Compared with sucrose or BR alone, the combined treatment increased fresh weight, hypocotyl length, AsA/DHA ratio, glutathione reductase activity, riboflavin, cellulose, and free amino acid contents, and decreased weight loss rate, browning index (BI), malondialdehyde (MDA) and dehydroascorbic acid content, ascorbate peroxidase and dehydroascorbate reductase activities in sprouts stored at low temperature. The riboflavin, cellulose, and free amino acid contents in the combined-treated group were higher 57.5%, 119.9%, and 66.7% than those in the control group of fresh samples (CK0), respectively, and there were no significant differences in BI and MDA content between CK0 and the combined-treated groups. These results indicated that the combination of sucrose and BR could better alleviate the reduced quality of kale sprouts stored at low temperature by regulating the weight loss rate and AsA-GSH cycle, so as to maintain the nutrients and antioxidant capacity of kale sprouts to the maximum extent.

Melatonin application suppresses oxidative stress and maintains fruit quality of cold stored ‘Esperanza’ raspberries by regulating antioxidant system

Raspberries are highly perishable and have a short storage life. To extend its storage life, we evaluated the impact of preharvest melatonin (MEL) application (0, 50, 100, 200 µmol L−1), three days before harvest, on the activities of oxidative and antioxidative enzymes and quality attributes in ‘Esperanza’ raspberries up to 10 d cold storage. The 200 µmol L−1 MEL-treated raspberries exhibited a significant reduction in disease incidence while maintaining higher marketable fruit and activities of superoxide dismutase, glutathione reductase, dehydroascorbate reductase, monodehydroascorbate reductase, ascorbate peroxidase and catalase as compared to control. Additionally, it reduced activities of polyphenol oxidase, peroxidase and lipoxygenase enzymes and increased flavonoids and ascorbic acid levels. However, preharvest spray of 100 µmol L−1 MEL mitigated fruit weight loss and maintained higher anthocyanins, and glutathione than control. In conclusion, MEL application (100–200 µmol L−1), three days before harvest, supressed oxidative stress by maintaining higher activities of antioxidant enzymes in raspberries during 10 d of cold storage.

Exogenous glutathione maintains the postharvest quality of mango fruit by modulating the ascorbate-glutathione cycle.

Mango fruit is prone to decay after harvest and premature senescence, which significantly lowers its quality and commercial value. The mango fruit (Mangifera indica L.cv. Guixiang) was treated with 0 (control), 2, 5, and 8 mM of reduced glutathione (GSH) after harvest. The fruit was stored at 25 ± 1 °C for 12 days to observe the changes in the antioxidant capacity and postharvest quality. Compared with the control, the 5 mM GSH treatment significantly decreased the weight loss by 44.0% and 24.4%, total soluble solids content by 25.1% and 4.5%, and soluble sugar content by 19.0% and 27.0%. Conversely, the 5 mM GSH treatment increased the firmness by 25.9% and 30.7% on days 4 and 8, respectively, and the titratable acidity content by 115.1% on day 8. Additionally, the 5 mM GSH treatment decreased the malondialdehyde and hydrogen peroxide contents and improved the antioxidant capacity of mango fruit by increasing the superoxide dismutase and peroxidase activities and upregulating the expression of the encoding genes. Meanwhile, the higher levels of monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase enzyme activities and gene expressions accelerated the AsA-GSH cycle, thereby increasing the accumulation of AsA and GSH and maintaining the redox balance. Overall, the experimental results suggest that 5 mM GSH maintains high antioxidant capacity and postharvest quality of mangoes and can use as an effective preservation technique for postharvest mangoes.