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Erysiphe alphitoides is a species of powdery mildew responsible for the major foliar disease of oak trees, including Quercus robur. Infection with E. alphitoides leads to a reduction in the growth of the trees and in their ability to survive. This paper reports on the biochemical changes characteristic of defence responses in oak leaves with different infection area sizes, collected in July, August, and September during three growing seasons. The study highlights the effect of E. alphitoides infection on changes in the ascorbate-glutathione cycle, phenolic compound profile, and metal content (mineral distribution). Visible symptoms of pathogen infection appeared gradually in July, but the most intense biochemical plant responses in oak leaves were detected mainly in August and September. These responses included increased ascorbate-glutathione enzyme activities, phenolic compounds, and metal contents. In addition, microscopic analyses revealed a strong fluorescence signal of lignin in the epidermis of pathogen-infected leaves. The involvement of the studied compounds in the basic defence mechanisms of oak against E. alphitoides infection is discussed in the paper. [ABSTRACT FROM AUTHOR]

The ascorbate-glutathione (AsA-GSH) cycle plays a critical role in scavenging hydrogen peroxide in plants and contributes significantly to plant stress tolerance. This study examines the cycle's response in Zostera marina seedlings to warming, specifically under conditions of abnormal sea temperature increase. Three temperature gradients were established: 18°C (control group), 23°C (high-temperature group), and 28°C (abnormally high-temperature group). Results after 7 days of exposure to mild high temperature (23°C) showed decreased MDA content in the HT group, increased AsA/DHA ratio, and enhanced activity of enzymes related to the AsA-GSH cycle. However, exposure to extreme high temperatures resulted in increased oxidative damage and redox imbalance in the AHT group. Initially, enzymes associated with the AsA-GSH cycle, such as APX, MDHAR, GPX, and γ-ECS, increased but significantly decreased later under stress. In contrast, DHAR and GaILDH levels significantly rose on the seventh day. Transcriptome analysis revealed upregulation of APX, MDHAR, DHAR, GR, and γ-ECS genes in the HT group, with a decline in other enzyme gene expressions by the seventh day, except for APX. Under extreme high temperatures, APX expression was downregulated early in the stress period, while DHAR was upregulated, indicating Z. marina seedlings can mitigate oxidative damage under short-term high temperatures by activating the AsA-GSH cycle. Conversely, extreme high temperatures may inhibit this cycle, disrupt redox balance, and adversely affect Z. marina seedling establishment, potentially leading to their demise. [ABSTRACT FROM AUTHOR]

Fresh-cut fruits, renowned for their convenience and nutritional value, are susceptible to rapid deterioration, compromising their quality and shelf life. In this study, a sustainable and environmentally friendly edible coating was developed based on sodium alginate (SA; 1% w/v), cedar mucilage (CM; 4% w/v), and calcium chloride (2% w/v), applied using a layer-by-layer technique to preserve the quality and prolong the shelf life of fresh-cut melon. Fruits were cut into cubes coated or uncoated by dipping and subsequently packaged in a polyethylene terephthalate container and stored for 15 days at 4 °C. Physicochemical traits and qualitative features such as polyphenol, flavonoid, carotenoid, ascorbic acid content, as well as antioxidant activity, were assessed. Furthermore, the enzymatic antioxidant system and the ascorbate–glutathione cycle were investigated. The coating reduced weight loss and enhanced polyphenol, flavonoid, and ascorbic acid content and antioxidant activity during cold storage. Edible coating (SA + CM) represents a valid tool to extend the postharvest life, improve the storability, and enhance the physicochemical and qualitative traits of fresh-cut melon. Further research is required to optimize coating formulations and application techniques to maximize their effectiveness and commercial viability in the food industry. [ABSTRACT FROM AUTHOR]

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.

Ascorbate peroxidase (APX), Monodehydroascorbate Reductase (MDAR), Dehydroascorbate Reductase (DHAR) and Glutathione Reductase (GR) enzymes participate in the ascorbate-glutathione cycle, which exerts a central role in the antioxidant metabolism in plants. Despite the importance of this antioxidant system in different signal transduction networks related to development and response to environmental stresses, the pathway has not yet been comprehensively characterized in many crop plants. Among different eudicotyledons, the Euphorbiaceae family is particularly diverse with some species highly tolerant to drought. Here the APX, MDAR, DHAR, and GR genes in Ricinus communis, Jatropha curcas, Manihot esculenta, and Hevea brasiliensis were identified and characterized. The comprehensive phylogenetic and genomic analyses allowed the classification of the genes into different classes, equivalent to cytosolic, peroxisomal, chloroplastic, and mitochondrial enzymes, and revealed the duplication events that contribute to the expansion of these families within plant genomes. Due to the high drought stress tolerance of Ricinus communis, the expression patterns of ascorbate-glutathione cycle genes in response to drought were also analyzed in leaves and roots, indicating a differential expression during the stress. Altogether, these data contributed to the characterization of the expression pattern and evolutionary analysis of these genes, filling the gap in the proposed functions of core components of the antioxidant mechanism during stress response in an economically relevant group of plants.

Citrus is mainly cultivated in acid soil with low boron (B) and high copper (Cu). In this study, Citrus sinensis seedlings were submitted to 0.5 (control) or 350 μM Cu (Cu excess or Cu exposure) and 2.5, 10, or 25 μM B for 24 weeks. Thereafter, H2O2 production rate (HPR), superoxide production rate (SAPR), malondialdehyde, methylglyoxal, and reactive oxygen species (ROS) and methylglyoxal detoxification systems were measured in leaves and roots in order to test the hypothesis that B addition mitigated Cu excess-induced oxidative damage in leaves and roots by reducing the Cu excess-induced formation and accumulation of ROS and MG and by counteracting the impairments of Cu excess on ROS and methylglyoxal detoxification systems. Cu and B treatments displayed an interactive influence on ROS and methylglyoxal formation and their detoxification systems. Cu excess increased the HPR, SAPR, methylglyoxal level, and malondialdehyde level by 10.9% (54.3%), 38.9% (31.4%), 50.3% (24.9%), and 312.4% (585.4%), respectively, in leaves (roots) of 2.5 μM B-treated seedlings, while it only increased the malondialdehyde level by 48.5% (97.8%) in leaves (roots) of 25 μM B-treated seedlings. Additionally, B addition counteracted the impairments of Cu excess on antioxidant enzymes, ascorbate-glutathione cycle, sulfur metabolism-related enzymes, sulfur-containing compounds, and methylglyoxal detoxification system, thereby protecting the leaves and roots of Cu-exposed seedlings against oxidative damage via the coordinated actions of ROS and methylglyoxal removal systems. Our findings corroborated the hypothesis that B addition alleviated Cu excess-induced oxidative damage in leaves and roots by decreasing the Cu excess-induced formation and accumulation of ROS and MG and by lessening the impairments of Cu excess on their detoxification systems. Further analysis indicated that the pathways involved in the B-induced amelioration of oxidative stress caused by Cu excess differed between leaves and roots. [ABSTRACT FROM AUTHOR]

Salicylic acid (SA) is a phytohormone and phenolic antioxidant that plays a role in various physiological and protective responses to biotic and abiotic stresses, including salinity. In this study, we analyzed the influence of 50 μM SA on wheat plants (Triticum aestivum L.) under 100 mM NaCl in a controlled growing experiment. Seed priming resulted in an increased activation of phenylalanine ammonia-lyase (PAL), tyrosine ammonia-lyase (TAL), and guaiacol peroxidase (GPX), as well as the accumulation of endogenous SA and lignin. It is likely that the accumulation of SA is responsible for the growth-stimulating effect of the phytohormone. SA priming led to the accumulation of reduced (GSH) and oxidized glutathione (GSSG) in a balanced manner, without altering the GSH/GSSG ratio, as well as the accumulation of ascorbic acid (ASA), hydrogen peroxide (H2O2), and the activation of glutathione reductase (GR) and ascorbate peroxidase (APX). In addition, these plants also exhibit a slight accumulation of carotenoids (Car) and proline. Under SA treatment, there is a decrease in stress-induced SA accumulation, along with additional lignin accumulation compared to the stress levels. This is accompanied by a decrease in stress-induced activation of PAL, TAL, and GPX. Strengthening the barrier properties of cell walls reduced the damaging effects of salinity on plants. This is evidenced by indicators such as the GSH/GSSG ratio, ASA and H2O2 content, Car levels, and the activation of APX and GR enzymes. Additionally, the state of membrane structures (MDA content and electrolyte leakage) and growth indicators also support this finding. The obtained data conclusively point to the realization that physiological and protective effects of SA are attributed to its ability to regulate its endogenous content, modify cell wall state, and reduce the damaging effects of stress on the state of the ascorbate-glutathione complex in wheat plants. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) plays an important role in plant growth, development, and stress responses. The exogenous NO donor sodium nitroprusside (SNP) increased the plant height, root length, and biomass of tomato seedlings under nitrate stress, especially 100 μM SNP. The reactive oxygen species (ROS) and malondialdehyde (MDA) contents were decreased, while the antioxidant enzyme activities, ascorbate and glutathione contents, and expression of SlTrxh, SlNTRB, SlTpx were increased in tomato after SNP and nitrate stress treatment, compared with nitrate stress. The tomato plants showed shorter root length, more MDA and ROS contents after the NADPH-dependent thioredoxin reductase (NTR) inhibitor Auranofin (ANF) was added, suggesting that ANF inhibited the alleviating effect of NO under nitrate stress. The NO and S-nitrosothiol (SNO) contents and the SlNR transcript levels were decreased and the expression of SlGLB, SlGSNOR was increased after NO and nitrate stress treatment. The S-nitrosylated level in tomato roots was increased after nitrate stress. The SlMDHAR, SlTrxh, and SlNTRB protein were S-nitrosylated after NO and nitrate stress treatment. These results suggested that key enzymes in ascorbate-glutathione cycle and Trx system played an important role in alleviating the effect of NO in tomato seedlings under nitrate stress involving the S-nitrosylation modification. [ABSTRACT FROM AUTHOR]

The effect of γ-aminobutyric acid (GABA) treatment on chilling injury in cold-stored kiwifruit and its relationship with reactive oxygen species (ROS) metabolism were investigated. Postharvest kiwifruit were treated with 2.0 mmol/L GABA solution for 20 min and stored at (4 ± 1) ℃ and (85 ± 5)% relative humidity. Chilling injury development was evaluated and the changes in the dynamic balance between the production and removal of ROS were analyzed. The results showed that compared with the control group, GABA treatment could delay the increases in the chilling injury index, cell membrane permeability and malondialdehyde (MDA) content of cold-stored kiwifruit, inhibit the rate of superoxide anion radical production and the increase in hydrogen peroxide content, and increase and maintain superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR) activities. Moreover, GABA treatment slowed down the decrease in the contents of ascorbic acid and glutathione, which contributed to higher antioxidant capacity levels in the fruit. The above findings indicated that exogenous GABA treatment could maintain dynamic redox balance, attenuate membrane lipid peroxidation and preserve cell membrane integrity in cold-stored kiwifruit by inhibiting the accumulation of ROS, and increasing the activities of the enzymatic and non-enzymatic ROS systems, thereby enhancing cold stress resistance and ultimately delaying chilling injury.

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The cooperative role of vital components of the antioxidative defense pathway in addition to redox couples was studied in a growth-phase dependent manner at 20, 30, and 40 days after subculturing (DAS) in five different euryhaline microalgal strains (EMS) Scenedesmus MKB (B-S), Spirulina subsalsa (B-6), Anabaena sp. (B-7), Chlorella sp. (B-8), and Chlorosarcinopsis eremi (B-18) collected from waterlogged areas of Punjab, India and in two freshwater microalgal strains (FMS). EMS surpasses to maintain a high redox couple's ratio ascorbic acid/dehydroascorbate (AsA/DHA), and reduced glutathione/oxidized glutathione (GSH/GSSG) through a close-knit pattern of antioxidative enzymes including high specific activities of ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), glutathione reductase (GR), dehydroascorbate reductase (DHAR) and less specific activity of glutathione peroxidase (GPX). While FMS struggled for the same irrespective of near similar total glutathione and higher specific activity of GPX might be answerable for the lesser redox ratio than EMS. However, high specific activity of catalase (CAT) might be sought to compensate for the less increase of APX in FMS. The fact significantly less H2O2, and malondialdehyde (MDA) with DAS in EMS than in FMS and higher redox ratios exquisitely elevate their tolerance ability making EMS a captivating prospect for cultivation in waterlogged areas. Additionally, their abundance of potent antioxidants further highlights the potential of EMS as an excellent source of these beneficial compounds. [ABSTRACT FROM AUTHOR]

The impact of climate change-induced drought stress on global food security and environmental sustainability is a serious concern. While previous research has highlighted the potential benefits of drought hardening in improving plants' ability to withstand drought, the exact underlying physiological mechanisms in millet plants (Setaria italica L.) have not been explored. This study aimed to investigate the impact of drought hardening on antioxidant defense and polyphenol accumulation in different millet genotypes ('PI 689680' and 'PI 662292') subjected to different treatments: control (unstressed), drought acclimation (two stress episodes with recovery), and non-acclimation (single stress episode with no recovery). The results showed that drought stress led to higher levels of polyphenols and oxidative damage, as indicated by increased phenolic, flavonoid, and anthocyanin levels. Non-acclimated (NA) plants experienced more severe oxidative damage and inhibition of enzymes associated with the ascorbate glutathione cycle compared to drought-acclimated plants. NA plants also exhibited a significant reduction in photosynthesis and tissue water content. The expression of genes related to antioxidants and polyphenol synthesis was more pronounced in non-acclimated plants. The study demonstrated that drought hardening not only prepared plants for subsequent drought stress but also mitigated damage caused by oxidative stress in plant physiology. Drought-acclimated (DA) plants displayed improved drought tolerance, as evidenced by better growth, photosynthesis, antioxidant defense, polyphenol accumulation, and gene expression related to antioxidants and polyphenol synthesis. In conclusion, the research advocates for the use of drought hardening as an effective strategy to alleviate the negative impacts of drought-induced metabolic disturbances in millet. [ABSTRACT FROM AUTHOR]

Erysiphe alphitoides is a species of powdery mildew responsible for the major foliar disease of oak trees, including Quercus robur. Infection with E. alphitoides leads to a reduction in the growth of the trees and in their ability to survive. This paper reports on the biochemical changes characteristic of defence responses in oak leaves with different infection area sizes, collected in July, August, and September during three growing seasons. The study highlights the effect of E. alphitoides infection on changes in the ascorbate-glutathione cycle, phenolic compound profile, and metal content (mineral distribution). Visible symptoms of pathogen infection appeared gradually in July, but the most intense biochemical plant responses in oak leaves were detected mainly in August and September. These responses included increased ascorbate-glutathione enzyme activities, phenolic compounds, and metal contents. In addition, microscopic analyses revealed a strong fluorescence signal of lignin in the epidermis of pathogen-infected leaves. The involvement of the studied compounds in the basic defence mechanisms of oak against E. alphitoides infection is discussed in the paper.

Fresh-cut fruits, renowned for their convenience and nutritional value, are susceptible to rapid deterioration, compromising their quality and shelf life. In this study, a sustainable and environmentally friendly edible coating was developed based on sodium alginate (SA; 1% w/v), cedar mucilage (CM; 4% w/v), and calcium chloride (2% w/v), applied using a layer-by-layer technique to preserve the quality and prolong the shelf life of fresh-cut melon. Fruits were cut into cubes coated or uncoated by dipping and subsequently packaged in a polyethylene terephthalate container and stored for 15 days at 4 °C. Physicochemical traits and qualitative features such as polyphenol, flavonoid, carotenoid, ascorbic acid content, as well as antioxidant activity, were assessed. Furthermore, the enzymatic antioxidant system and the ascorbate–glutathione cycle were investigated. The coating reduced weight loss and enhanced polyphenol, flavonoid, and ascorbic acid content and antioxidant activity during cold storage. Edible coating (SA + CM) represents a valid tool to extend the postharvest life, improve the storability, and enhance the physicochemical and qualitative traits of fresh-cut melon. Further research is required to optimize coating formulations and application techniques to maximize their effectiveness and commercial viability in the food industry.

Citrus is mainly cultivated in acid soil with low boron (B) and high copper (Cu). In this study, Citrus sinensis seedlings were submitted to 0.5 (control) or 350 μM Cu (Cu excess or Cu exposure) and 2.5, 10, or 25 μM B for 24 weeks. Thereafter, H2O2 production rate (HPR), superoxide production rate (SAPR), malondialdehyde, methylglyoxal, and reactive oxygen species (ROS) and methylglyoxal detoxification systems were measured in leaves and roots in order to test the hypothesis that B addition mitigated Cu excess-induced oxidative damage in leaves and roots by reducing the Cu excess-induced formation and accumulation of ROS and MG and by counteracting the impairments of Cu excess on ROS and methylglyoxal detoxification systems. Cu and B treatments displayed an interactive influence on ROS and methylglyoxal formation and their detoxification systems. Cu excess increased the HPR, SAPR, methylglyoxal level, and malondialdehyde level by 10.9% (54.3%), 38.9% (31.4%), 50.3% (24.9%), and 312.4% (585.4%), respectively, in leaves (roots) of 2.5 μM B-treated seedlings, while it only increased the malondialdehyde level by 48.5% (97.8%) in leaves (roots) of 25 μM B-treated seedlings. Additionally, B addition counteracted the impairments of Cu excess on antioxidant enzymes, ascorbate-glutathione cycle, sulfur metabolism-related enzymes, sulfur-containing compounds, and methylglyoxal detoxification system, thereby protecting the leaves and roots of Cu-exposed seedlings against oxidative damage via the coordinated actions of ROS and methylglyoxal removal systems. Our findings corroborated the hypothesis that B addition alleviated Cu excess-induced oxidative damage in leaves and roots by decreasing the Cu excess-induced formation and accumulation of ROS and MG and by lessening the impairments of Cu excess on their detoxification systems. Further analysis indicated that the pathways involved in the B-induced amelioration of oxidative stress caused by Cu excess differed between leaves and roots.

Aluminum (Al) toxicity causes a substantial crop productivity loss in acid soil. Here, we evaluated the antioxidant responses and metabolic adjustments in soybean roots after Al exposure and demonstrated that different genotypes from the same species can present distinctive strategies to avoid Al toxicity. Soybean genotypes were exposed to nutrient Clark solution (pH 4.0) under two cultivation conditions: 0 µM (control) and 100 µM AlCl3 for 24, 48, and 72 h. Our results demonstrated that the soybean genotypes 'P98Y70' and 'Conquista' present different tolerance to Al. The root growth of P98Y70 genotype was impaired under Al treatment. Besides, this genotype showed a delay and lower activities in their antioxidant enzymes, which culminates in a high accumulation of reactive oxygen species (ROS). On the other hand, the Conquista genotype showed an early antioxidant enzymatic response through the increase in the superoxide dismutase (SOD), catalase (CAT), and total peroxidase (POX) activities at 24 h of Al exposure, whereas P98Y70 showed high SOD and POX activities only at 72 h. Besides, the Conquista genotype presented high levels of ascorbate, fructose-6-phosphate (F6P), and high activity in the glutathione peroxidase (GPX), which culminated in a low accumulation of ROS and less oxidative stress. Therefore, these traits can be used as biomarkers of Al tolerance in soybean plants when associated with an early response against Al. [ABSTRACT FROM AUTHOR]

Facing climate change, the development of innovative agricultural technologies securing food production becomes increasingly important. Plasma-treated water (PTW) might be a promising tool to enhance drought stress tolerance in plants. Knowledge about the efects of PTW on the physiology of plants, especially on their antioxidative system on a long-term scale, is still scarce. In this work, PTW was applied to barley leaves (Hordeum vulgare cv. Kosmos) and various constituents of the plants’ antioxidative system were analyzed 30 days after treatment. An additional drought stress was performed after foliar PTW application followed by a recovery period to elucidate whether PTW treatment improved stress tolerance. Upon PTW treatment, the Total Antioxidant Capacity (TAC) in leaves and roots was lower in comparison to deionized water treated plants. In contrast, PTW treatment caused a higher content of chlorophyll, quantum yield and total ascorbate content in leaves compared to deionized water treated plants. After additional drought application and subsequent recovery period, an enhancement of values for TAC, contents of malondialdehyde, glutathione as well as activity of ascorbate peroxidase indicated a possible upregulation of antioxidative properties in roots. Hydrogen peroxide and nitric oxide might mediate abiotic stress tolerance and are considered as key components of PTW. [ABSTRACT FROM AUTHOR]

Black spot rot caused by Alternaria alternata is one of the major postharvest disease of apple fruit during logistic. This study evaluated in vitro inhibitory effect of 2-hydroxy-3-phenylpropanoic acid (PLA) at various concentrations on A. alternata and the possible mechanisms involved in its action. Results showed that different concentrations of PLA inhibited conidia germination and mycelial growth of A. alternata in vitro, and 1.0 g L−1 was the lowest effective concentration to suppress A. alternata growth. Moreover, PLA significantly reduced relative conductivity and increased malondialdehyde and soluble protein contents. PLA also increased H 2 O 2 and dehydroascorbic acid contents, but reduced ascorbic acid content. Additionally, PLA treatment inhibited catalase, ascorbate peroxidase, monodehydroascorbate acid reductase, dehydroascorbic acid reductase and glutathione reductase activities, whereas promoted superoxide dismutase activity. All these findings suggest that the possible mechanisms involved in the inhibitory effect of PLA on A. alternata included damaging the cell membrane integrity to cause electrolyte leakage and destroying reactive oxygen species balance. • 2-hydroxy-3-phenylpropanoic acid inhibited conidia germination and mycelial growth of Alternaria alternata. • 2-hydroxy-3-phenylpropanoic acid destroyed the reactive oxygen species balance in A. alternata to inhibit its growth. • 2-hydroxy-3-phenylpropanoic acid damaged the cell membrane integrity of A. alternata. [ABSTRACT FROM AUTHOR]

Malus baccata Borkh., an apple rootstock, is found to be damaged by oxidation at sub-low root-zone temperature. In previous studies, we have found that exogenous sucrose could alleviate oxidative damage and increase the indole acetic acid (IAA) in roots under sub-low temperature (L). However, the role of IAA in sucrose-induced tolerance to L remains unclear. A pot experiment was conducted to evaluate the effects of exogenous sucrose and IAA synthesis/transport inhibitors (2,3,5-triiodobenzoic acid, TIBA; 4-biphenylboronic acid, BBo) on growth, IAA levels, sugars, and the antioxidant system of M. baccata under L. The results showed that the L treatment decreased IAA contents by 23.69% (48 h) and induced significant increases in root contents of malondialdehyde (MDA) and reactive oxygen (ROS), along with increasing catalase (CAT), ascorbate peroxidase (APX), and glucose-6-phosphate dehydrogenase (G6PDH) activities, while superoxide dismutase (SOD) and monodehydroascorbate reductase (MDHAR) activities first increased (24 h) and then decreased (48 h), and glutathione reductase (GR) and peroxidase (POD) activities significantly decreased. The L treatment also decreased ascorbate/oxidized ascorbate (AsA/DHA), glutathione/oxidized glutathione (GSH/GSSG), and coenzyme II/oxidized coenzyme II (NADPH/NADP+) ratios. Furthermore, the L treatment increased the contents of sucrose, fructose, glucose and sorbitol in the roots and suppressed plant growth. Sucrose pretreatment significantly increased IAA contents (12.42%, 24 h and 14.44%, 48 h) and decreased MDA and ROS contents, which improved the activities of antioxidant enzymes other than APX and increased the contents of AsA, GSH, and NADPH, and increased sucrose, fructose, and sorbitol contents and promoted plant growth. However, the sucrose + TIBA or BBo treatments decreased IAA contents and attenuated or almost abolished the positive effects of exogenous sucrose under sub-low temperature. Our findings indicate that IAA is involved in the sucrose-induced regulation of the antioxidant system in M. baccata roots under sub-low temperature and we provided theoretical references for further study on the adaptability of apple roots to low temperature. [ABSTRACT FROM AUTHOR]

Simple Summary: The climatic changes pose important threats to agriculture. Plants are sessile organisms and need to cope with different environmental conditions throughout their lifespan. Most responses involve different signaling molecules, including reactive oxygen species (ROS). Due to their high reactivity, ROS are also an oxidative threat to the cell. Consequently, plant cells display elaborated defenses against oxidative stress. The ascorbate-glutathione cycle is the main antioxidant pathway in photosynthetic organisms and is composed by the enzymes ascorbate peroxidase (APX), monodehydroascorbate reductase (MDAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR). Here, the APX, MDAR, DHAR and GR genes from castor bean, cassava, jatropha and rubber tree were identified and classified. This classification allowed the prediction of their subcellular localization within plant cells, such as cytosol, peroxisomes, chloroplasts, and mitochondria. Our analysis also contributes to understanding the evolutionary history of these genes. The expression pattern of ascorbate-glutathione cycle genes in castor bean submitted to drought reveals changes in leaves and roots. Altogether, these data contribute to uncovering the regulation of ROS metabolism during stress response in castor bean, which is highly tolerant to drought. Ascorbate peroxidase (APX), Monodehydroascorbate Reductase (MDAR), Dehydroascorbate Reductase (DHAR) and Glutathione Reductase (GR) enzymes participate in the ascorbate-glutathione cycle, which exerts a central role in the antioxidant metabolism in plants. Despite the importance of this antioxidant system in different signal transduction networks related to development and response to environmental stresses, the pathway has not yet been comprehensively characterized in many crop plants. Among different eudicotyledons, the Euphorbiaceae family is particularly diverse with some species highly tolerant to drought. Here the APX, MDAR, DHAR, and GR genes in Ricinus communis, Jatropha curcas, Manihot esculenta, and Hevea brasiliensis were identified and characterized. The comprehensive phylogenetic and genomic analyses allowed the classification of the genes into different classes, equivalent to cytosolic, peroxisomal, chloroplastic, and mitochondrial enzymes, and revealed the duplication events that contribute to the expansion of these families within plant genomes. Due to the high drought stress tolerance of Ricinus communis, the expression patterns of ascorbate-glutathione cycle genes in response to drought were also analyzed in leaves and roots, indicating a differential expression during the stress. Altogether, these data contributed to the characterization of the expression pattern and evolutionary analysis of these genes, filling the gap in the proposed functions of core components of the antioxidant mechanism during stress response in an economically relevant group of plants. [ABSTRACT FROM AUTHOR]

Low temperature combined with low light (LL) affects crop production, especially the yield and quality of peppers, in northwest China during the winter and spring seasons. Zeaxanthin (Z) is a known lipid protectant and active oxygen scavenger. However, whether exogenous Z can mitigate LL-induced inhibition of photosynthesis and oxidative stress in peppers remains unclear. In this study, we investigated the effects of exogenous Z on photosynthesis and the antioxidant machinery of pepper seedlings subject to LL stress. The results showed that the growth and photosynthesis of pepper seedlings were significantly inhibited by LL stress. In addition, the antioxidant machinery was disturbed by the uneven production and elimination of reactive oxygen species (ROS), which resulted in damage to the pepper. For example, membrane lipid peroxidation increased ROS content, and so on. However, exogenous application of Z before LL stress significantly increased the plant height, stem diameter, net photosynthetic rate (Pn), and stomata, which were obviously closed at LL. The activities of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), mono de-hydroascorbate reductase (MDHAR), de-hydroascorbate reductase (DHAR), ascorbate peroxidase (APX), and ascorbate oxidase (AAO) improved significantly due to the increased expression of CaSOD, CaCAT, CaAPX, CaMDHAR, and CaDHAR. The ascorbic (AsA) and glutathione (GSH) contents and ascorbic/dehydroascorbate (AsA/DHA) and glutathione/oxidized glutathione (GSH/GSSG) ratios also increased significantly, resulting in the effective removal of hydrogen peroxide (H2O2) and superoxide anions (O2•−) caused by LL stress. Thus, pre-treatment with Z significantly reduced ROS accumulation in pepper seedlings under LL stress by enhancing the activity of antioxidant enzymes and accumulation of components of the ascorbate–glutathione (AsA–GSH) cycle and upregulated key genes in the AsA–GSH cycle.

Aluminum (Al) is a major environmental stress that limits crop growth and production. 24-Epibrassinolide (EBR) can control stress responses, but how it regulates Al homeostasis in Al-stressed maize seedlings is poorly understood. Therefore, seedlings of two lines of maize (Zea mays L.) under Al stress (60 μM AlCl3) were treated with 1.0 × 10−6 M EBR. In roots exposed to Al, EBR helped protect membranes and reduced reactive oxygen species by activating antioxidant enzymes, the ascorbate-glutathione cycle, phytohormone signal, and proline accumulation. In leaves under Al stress, EBR increased photosynthetic performance by protecting chloroplast ultrastructure, increasing ribulose 1,5-biphosphate carboxylase activity, and improving gas exchange. With EBR, inhibiting photoinhibition and promoting photosystem II efficiency maximized chlorophyll fluorescence. Changes in expression levels of ten candidate genes associated with antioxidant enzymes, phytohormone signals, mitogen-activated protein kinase (MAPK) pathway, photosynthesis, and chlorophyll fluorescence were consistent with changes in physiological assays in maize seedlings in the different treatments. Therefore, EBR can help alleviate Al toxicity in maize by improving activity in multiple metabolic pathways. [ABSTRACT FROM AUTHOR]

Numerous advances have been made to mitigate the repercussion of toxic metals on photosynthetic prokaryotes, i.e. cyanobacteria. One strategy is exogenous supplementation of plant growth regulators (PGRs). This perhaps intensifies the resistance ability of cyanobacteria to encounter the environmental stresses by augmenting their physiological functioning and decontaminant efficiency. Thus, the aim of the present study was to determine if the PGRs auxin (indole-3 acetic acid, IAA; 300 nM) and cytokinin (kinetin, KN; 10 nM) are able to mitigate the toxic environmentally relevant doses of chromium (CrVI; 100 and 150 µM) in cyanobacteria (Nostoc muscorum ATCC 27,683 and Anabaena sp. PCC 7120). The response was assessed by estimating oxidative stress [in vitro and in vivo (superoxide radical; O2·−, hydrogen peroxide H2O2 and malondialdehyde equivalents contents; MDA)], feasible alteration in whole cell oxygen evolution, ascorbate–glutathione cycle and their metabolites. Intracellular Cr accumulation raised the production of ROS by down-regulating the photosynthetic rate due to decreased pigment contents (Chl a; chlorophyll a, Car; carotenoids and PC; phycocyanin) and reduced growth despite the accelerated activity of the ascorbate–glutathione (AsA-GSH) cycle enzymes (viz. APX; ascorbate peroxidase, GR; glutathione reductase and DHAR; dehydroascorbate reductase). Concurrently, exogenous PGRs (auxin and cytokinin) moderated the negative effects of Cr on the growth, by lowering the cellular Cr accumulation and ROS level and by modulating the pigment system, photosynthesis and a further rise in the efficiency of AsA-GSH cycle, thereby acting as positive regulators of the metal detoxification machinery. Thus, exogenous application of PGRs (auxin and cytokinin) could improve the growth in cyanobacteria in Cr-polluted environments, hence maintaining productivity in paddy cultivation as well as having potential to be used as bio-remediator in metal-contaminated aquatic systems. [ABSTRACT FROM AUTHOR]

24-epibrassinolide (EBR) application has been proven to be effective in the control of gray mold (Botrytis cinerea) and preservation in table grape, however, the possible underlying mechanism of EBR on maintaining the postharvest quality and controlling gray mold of table grape are incompletely understood. In this study, the application of EBR at veraison (T1) and postharvest (T2) could effectively alleviate the quality deterioration of table grapes during storage, as observed by higher fruit firmness, rachis chlorophyll content, titratable acidity, and total soluble solid, and lower shattering rate, decay incidence, weight loss rate, browning index and relative electrolyte leakage of rachis, and respiration rate. Moreover, EBR application inhibited the excess accumulation of superoxide anion, hydrogen peroxide (H 2 O 2), malondialdehyde, and the expression of hydrogen peroxide sensor (HPCA) genes (VvHPCA1 , VvHPCA2 , and VvHPXA3). In addition, T1 and T2 treatments resulted in higher activities of superoxide dismutase, peroxidase, catalase, and superoxide anion, as well as the expression level of their corresponding gene expression. A considerable increase in key enzyme activities, antioxidant content, and gene expression in the ascorbate-glutathione (ASA-GSH) cycle was also observed in grape fruit treated with EBR. Importantly, the multivariate statistical analysis revealed that T2 treatment had a more remarkable effect on preserving the quality of postharvest grapes. In addition, under artificial infections, EBR treatment significantly reduced gray mold severity in table grapes and reduced malondialdehyde and superoxide anion generation while exhibiting no antifungal activity in vitro. Simultaneously, defensive enzyme activities, including peroxidase, polyphenol oxidase, chitinase, and β-1,3-glucanase, were remarkably increased in fruit treated with EBR. Therefore, our findings suggest that exogenous application of EBR maintains the quality of postharvest grapes and improves the resistance of table grapes to gray mold during postharvest storage by regulating oxidative stress and the activity of antioxidant enzymes and defensive enzymes. ● EBR treatment at veraison or at preharvest all delayed the postharvest quality deterioration in table grape. ● EBR improved the resistance against to B. cinerea in vivo of table grape but not in vitro. ● EBR reduced the accumulation of O 2 •−, H 2 O 2 , and MDA content, and inhibited the expression of hydrogen peroxide sensors. ● EBR activated enzymatic antioxidant defense system in table grape. ● VvHPCA2 and VvHPCA3 could be used as candidate genes to evaluate the degree of oxidative damage. [ABSTRACT FROM AUTHOR]

Melatonin (MT) is an important biologically active hormone that plays a vital role in plant growth and development. In particular, it has been investigated for its roles in abiotic stress management. In this study, pepper seedlings were subjected to low-temperature combined with low-light stress (LL) (15/5°C, 100 μmolm-2s-1) prior to a foliar spray of 200mM MT for 168h to investigate the protective role of MT in pepper seedlings. Our results demonstrated that LL stress negatively affected root growth, and accelerated the accumulation of reactive oxygen species (ROS), including H2O2 and O-2, changed the osmolytes contents, and antioxidative system. However, these were reversed by exogenous MT application. MT effectively promoted the root growth as indicated by significant increase in root length, surface area, root volume, tips, forks, and crossings. In addition, MT reduced the burst of ROS and MDA contents induced by LL, enhanced the activities of SOD, CAT, POD, APX, DHAR, and MDHAR resulted by upregulated expressions of CaSOD, CaPOD, CaCAT, CaAPX, CaDHAR, and CaMDHAR, and elevated the contents of AsA and GSH, declined DHA and GSSH contents, which prevented membrane lipid peroxidation and protected plants from oxidative damages under LL stress. Furthermore, seedlings treated with MT released high contents of soluble sugar and soluble protein in leave, which might enhance LL tolerance by maintaining substance biosynthesis and maintaining cellular homeostasis resulted by high levels of osmolytes and carbohydrate in the cytosol. Our current findings confirmed the mitigating potential of MT application for LL stress by promoting pepper root growth, improving antioxidative defense system, ascorbate-glutathione cycle, and osmotic adjustment. [ABSTRACT FROM AUTHOR]

Plant growth and development are closely related to water availability. Water deficit and water excess are detrimental to plants, causing a series of damage to plant morphology, physiological and biochemical processes. In the long evolutionary process, plants have evolved an array of complex mechanisms to combat against stressful conditions. In the present study, the durationdependent changes in ascorbate (AsA) and glutathione (GSH) contents and activities of enzymes involved in the AsA-GSH cycle in hairgrass (Deschampsia caespitosa) in response to water stress was investigated in a pot trial using a complete random block design. The treatments were as follows: (1) heavily waterlogging, (2) moderate waterlogging, (3) light waterlogging, (4) light drought, (5) moderate drought, (6) heavily drought, and (7) a control (CK) with plant be maintained at optimum water availability. The hairgrass plants were subjected to waterlogging or drought for 7, 14, 21 and 28 days and data were measured following treatment. Results revealed that hairgrass subjected to water stress can stimulate enzymatic activities of ascorbate peroxidase (APX), glutathione peroxidase (GPX), glutathione reductase (GR), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR) and L-galactono-1, 4-lactone dehydrogenase (GalLDH), switched on the ascorbate-glutathione (AsA-GSH) cycle and the L-galactose synthesis, up-regulated the contents of AsA and GSH, and maintained higher ratios of ascorbate to dehydroascorbate (AsA/DHA) and reduced glutathione to oxidized glutathione (GSH/GSSG) to alleviate potential oxidative damage. However, the light waterlogging did not induce hairgrass under stress to switch on the AsAGSH pathway. In general, the critic substances and enzyme activities in AsAGSH metabolic pathway increased as the increase of water stress intensity. As the increase of exposure duration, the critic antioxidant substances content and enzyme activities increased first and then maintained a relatively stable higher level. Our findings provide comprehensive information on biochemical responses of hairgrass to hydrological change, which would be a major step for accelerating ecological restoration of degradation alpine marshes in the Qinghai-Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Triticum aestivum L. cv. Gazul is a spring wheat widely cultivated in Castilla y León (Spain). Potted plants were grown in a scenario emulating the climate change environmental conditions expected by the end of this century, i.e., with elevated CO2 and high temperature under two water deficit regimes: long (LWD) and terminal (TWD). Changes in biomass and morphology, the content of proline (Pro), ascorbate (AsA) and glutathione (GSH), and enzymatic antioxidant activities were analyzed in flag leaves and ears. Additionally, leaf gas exchange was measured. LWD caused a decrease in biomass and AsA content but an increase in Pro content and catalase and GSH reductase activities in flag leaves, whereas TWD produced no significant changes. Photosynthesis was enhanced under both water deficit regimes. Increase in superoxide dismutase activity and Pro content was only observed in ears under TWD. The lack of a more acute effect of LWD and TWD on both organs was attributed to the ROS relieving effect of elevated CO2. Gazul acted as a drought tolerant variety with anisohydric behavior. A multifactorial analysis showed better adaptation of ears to water deficit than flag leaves, underlining the importance of this finding for breeding programs to improve grain yield under future climate change. [ABSTRACT FROM AUTHOR]

Peach (Prunus persica (L.) Batsch) is susceptible to chilling injury under improper low-temperature storage (2°C-5°C). Previous research has shown that abscisic acid (ABA) alleviates chilling injury in fruits and vegetables, but the potential mechanism is still unclear. To explore its effectiveness and potential mechanism in alleviating chilling injury during cold storage, exogenous ABA was applied to peach fruit by immersion in 100 μmol L-1 solutions for 10 min. In our experiment, ABA alleviated chilling injury by reducing hydrogen peroxide (H2O2) content and ethylene production. In addition, ABA inhibited the expression of the ethylene synthesis-related genes PpACO1 and PpEIN2. At the same time, ABA activated the antioxidant enzymatic pathway and the ascorbate-glutathione (AsA-GSH) cycle, the transcript abundance encoding genes related to antioxidant enzyme activities also changed correspondingly. The results suggested that ABA alleviated chilling injury by scavenging excessive H2O2 by promoting antioxidant enzymes and the AsA-GSH pathway. [ABSTRACT FROM AUTHOR]

Mechanical wound on fruit triggers the formation of reactive oxygen species (ROS) that weaken cell walls, resulting in post-harvest losses. This mechanism can be controlled by using fruit preservatives to stimulate fruit antioxidant enzyme activities for the detoxification of ROS. Chitosan is a safe and environmentally friendly preservative that modulates ROS in whole fruits and plant cells, but the effects of chitosan on the ROS metabolism of mechanically wounded apples during storage are unknown. Our study focused on exploring the effects of post-harvest chitosan treatment on ROS production, cell membrane integrity, and enzymatic and non-enzymatic antioxidant systems at fruit wounds during storage. Apple fruits (cv. Fuji) were artificially wounded, treated with 2.5% (w/v) chitosan, and stored at room temperature (21--25°C, RH = 81--85%) for 7 days. Non-wounded apples were used as healthy controls. The results showed that chitosan treatment stimulated the activities of NADPH oxidase and superoxide dismutase and increased the formation of superoxide anions and hydrogen peroxide in fruit wounds. However, malondialdehyde, lipoxygenase, and membrane permeability, which are direct biomarkers to evaluate lipid peroxidation and membrane integrity, were significantly decreased in the wounded fruits after chitosan treatment compared to the wounded control fruits. Antioxidant enzymes, such as peroxidase and catalase activities, were induced by chitosan at fruit wounds. In addition, ascorbate-glutathione cycle-related enzymes; ascorbate peroxide, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase and the content of substrates, mainly ascorbic acid, dehydroascorbate, reduced glutathione, and glutathione, were increased at fruit wounds by chitosan compared to the wounded control fruits. Our results show that wounding stimulated the production of ROS or oxidative [ABSTRACT FROM AUTHOR]

Contamination of soil with chromium (Cr) is a rising problem in terms of agricultural sustainability and food safety. Here, the effects of methyl jasmonate (MJ; 0, 5, and 10 µM) on alleviating Cr stress (0, 100, and 200 µM) were surveyed in pot marigold (Calendula officinalis L.). The results showed that Cr stress significantly reduced photosynthetic pigments and leaf accumulation of total soluble sugars, total starch, and mineral nutrients and, consequently, lowered the height and biomass of pot marigold plants. Chromium toxicity also increased the leaf levels of oxidative stress markers and induced oxidative stress, which was associated with damage to bio-membranes and increased levels of malondialdehyde. However, MJ supplementation reduced the leaf accumulation of Cr, increased the content of photosynthetic pigments, and improved the performance of the photosynthetic machinery in Cr-stressed plants. MJ supplementation boosted the antioxidant defense system by upregulating antioxidant enzymes, glyoxalase enzymes, and the ascorbate-glutathione (AsA-GSH) pool redox, which significantly diminished Cr-induced oxidative stress. Hence, MJ supplementation might be a practicable approach for reducing Cr absorption and its negative impacts on pot marigold plants growing under Cr-contaminated conditions. Clinical trials registration Not applicable. [ABSTRACT FROM AUTHOR]

Mechanical wound on fruit triggers the formation of reactive oxygen species (ROS) that weaken cell walls, resulting in post-harvest losses. This mechanism can be controlled by using fruit preservatives to stimulate fruit antioxidant enzyme activities for the detoxification of ROS. Chitosan is a safe and environmentally friendly preservative that modulates ROS in whole fruits and plant cells, but the effects of chitosan on the ROS metabolism of mechanically wounded apples during storage are unknown. Our study focused on exploring the effects of post-harvest chitosan treatment on ROS production, cell membrane integrity, and enzymatic and non-enzymatic antioxidant systems at fruit wounds during storage. Apple fruits (cv. Fuji) were artificially wounded, treated with 2.5% (w/v) chitosan, and stored at room temperature (21–25°C, RH = 81–85%) for 7 days. Non-wounded apples were used as healthy controls. The results showed that chitosan treatment stimulated the activities of NADPH oxidase and superoxide dismutase and increased the formation of superoxide anions and hydrogen peroxide in fruit wounds. However, malondialdehyde, lipoxygenase, and membrane permeability, which are direct biomarkers to evaluate lipid peroxidation and membrane integrity, were significantly decreased in the wounded fruits after chitosan treatment compared to the wounded control fruits. Antioxidant enzymes, such as peroxidase and catalase activities, were induced by chitosan at fruit wounds. In addition, ascorbate-glutathione cycle-related enzymes; ascorbate peroxide, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase and the content of substrates, mainly ascorbic acid, dehydroascorbate, reduced glutathione, and glutathione, were increased at fruit wounds by chitosan compared to the wounded control fruits. Our results show that wounding stimulated the production of ROS or oxidative stress. However, treatment with chitosan triggered antioxidant systems to scavenge ROS and prevent loss of fruit membrane integrity. Therefore, chitosan promises to be a favorable preservative in inducing tolerance to stress and maintaining fruit quality.

Pistia stratiotes is a cadmium (Cd) hyperaccumulating plant with strong bioaccumulation and translocation capacity for Cd. A hydroponic experiment was used to evaluate the combined effect of Zinc (Zn) and Cd at different concentrations on leaf growth and metabolism of P. stratiotes. This study revealed the physiological defense and metabolic strategy of responses to Zn–Cd co-pollution. With the Zn 50 Cd 1 , Zn 50 Cd 10 , Zn 100 Cd 1, and Zn 100 Cd 10 treatments for 9 d, the relative crown diameter, relative leave number, and ramet number of the plant had no significant difference with the control. Under the compound treatments containing Zn 50 Cd 50 and Zn 100 Cd 50 , the activity of the glyoxalase system and amino acid metabolism in the leaves were inhibited. The leaf photosynthetic apparatus increased heat dissipation to reduce the damage to the photosystem II (PS II) reaction center caused by excess excitation energy under Zn–Cd stress. This safeguarded the balance between the absorption and utilization of light energy. Compared to the control, the Zn and Cd co-pollution for 9 d had no effect on the reduced glutathione (GSH) and oxidized glutathione (GSSG) contents. There was no effect on the dehydroascorbate reductase (DHAR) and glutathione reductase (GR) activities, but there was increased ascorbate peroxidase (APX) activity and oxidized ascorbic acid (DHA) content. These increased the antioxidant capacity of the ascorbate-glutathione (AsA-GSH) cycle. The treated plants also had increased levels of carnosol and substances related to lipid metabolism including 9, 10-Dihydroxystearate, Prostaglandin G2, Sphingosine, and 13-L-Hydroperoxylinoleic acid, maintaining the cell stability and resistance to the Zn–Cd stress. [Display omitted] • The redox reaction equilibrium of glutathione maintained the antioxidant stability. • Increased carnosol and lipid metabolism were conducive to zinc-cadmium tolerance. • Pistia stratiotes can be used for phytoremediation of zinc-cadmium polluted water. [ABSTRACT FROM AUTHOR]

The present study aimed to study the effect of dry leaf and stem leachates of Acacia saligna on wheat's growth and enzyme functioning (Triticum aestivum) and barley (Hordeum vulgare). Leaf leachates (LL) and stem leachates (SL) of A. saligna were applied through root and nutrient solution in different concentrations i.e., 5, 10, and 15%. Treatment of LL and SL declined the growth in terms of height and dry weight in both tested plants in concentration-dependent manner with the maximal decline due to 15% LL. In addition, content of relative water, total chlorophylls, and carotenoids decreased in both wheat as well as barley. The activity of ascorbate peroxidase, monodehydro ascorbate reductase, dehydroascorbate reductase, and glutathione reductase increased considerably due to the treatment of LL and SL. The indigenous tolerance mechanisms in wheat and barley seedlings were further strengthened in wheat and barley by increased accumulation of glycine betaine, glutathione, and ascorbate in response to LL and SL treatment. Additionally, the activity of lipoxygenase and protease were increased significantly due to LL and SL treatment with a maximal increase at higher concentrations. From the present study it can be concluded that extracts of leaf and stem of A. saligna inhibit the growth of wheat and barley significantly with a concomitant increase in the functioning of the ascorbate-glutathione (AsA-GSH) cycle. Further, both crop species showed comparable responses to A. saligna leachates. [ABSTRACT FROM AUTHOR]

Antioxidants and phytohormones are hallmarks of abiotic stress responses in plants. Although it is known that they can offer cell protection or accelerate programmed cell death (PCD) depending on the level of stress, the involvement of these metabolites in stress acclimation is still not fully elucidated. Here, we showed the role of antioxidants and phytohormones in Salvia officinalis tolerance to long-term ozone (O3) exposure (120 ppb for 36 days, 5 h day−1). Salicylic acid (SA) content was increased under O3 throughout the whole experiment (+150%, as average compared with control), being required to maintain the cellular redox state and potentiate defense responses. This accumulation was induced before the production of ethylene (ET), suggesting that ET was controlled by SA during O3 exposure to modulate the magnitude of chlorosis formation and the cell redox balance (by regulating ascorbate and glutathione levels). The synthesis and/or regeneration of these antioxidants did not protect membranes from lipid peroxidation, as demonstrated by the accumulation of malondialdehyde (+23% as average). However, these processes of lipid oxidation did not include the synthesis of the membrane breakdown products, as confirmed by the unchanged values of jasmonic acid, thus indicating that this compound was not involved in the regulation of PCD strategies. [ABSTRACT FROM AUTHOR]

Rambutan is a famous tropical fruit with a unique flavor and considerable economic value. However, the high vulnerability to postharvest browning leads to a short shelf life of rambutan fruit. Melatonin (MT) is an excellent bioactive molecule that possesses the potential to improve the storability of the harvested crops. In this study, the physiological mechanism of exogenous MT in affecting pericarp browning and senescence of postharvest rambutan fruit was investigated. Experimental results showed that the application of MT at 0.125 mmol L–1 appreciably retarded the advancement of pericarp browning and color parameters (L*, a*, and b*). MT treatment inhibited the increase in membrane relative electrolytes leakage (REL) while lowering the accumulation of reactive oxygen species (ROS) (■O2– and H2O2) and malonaldehyde (MDA). Reduced phenolics oxidation, as indicated by higher contents of total phenolics, flavonoids, and anthocyanins along with fewer activities of peroxidase (POD) and polyphenol oxidase (PPO), was detected in MT fruit compared with control fruit. MT treatment maintained the cellular redox state by inducing antioxidant enzyme activity and reinforcing the ascorbate-glutathione (AsA-GSH) cycle. Furthermore, the ultrastructural observation revealed that the spoilage of cellular and subcellular structures was milder in MT fruit than that in control fruit. The results suggest that MT could ameliorate the browning and senescence of rambutan fruit by inhibiting phenolic oxidation and enhancing the antioxidative process.

The present study aimed to study the effect of dry leaf and stem leachates of Acacia saligna on wheat’s growth and enzyme functioning (Triticum aestivum) and barley (Hordeum vulgare). Leaf leachates (LL) and stem leachates (SL) of A. saligna were applied through root and nutrient solution in different concentrations i.e., 5, 10, and 15%. Treatment of LL and SL declined the growth in terms of height and dry weight in both tested plants in concentration-dependent manner with the maximal decline due to 15% LL. In addition, content of relative water, total chlorophylls, and carotenoids decreased in both wheat as well as barley. The activity of ascorbate peroxidase, monodehydro ascorbate reductase, dehydroascorbate reductase, and glutathione reductase increased considerably due to the treatment of LL and SL. The indigenous tolerance mechanisms in wheat and barley seedlings were further strengthened in wheat and barley by increased accumulation of glycine betaine, glutathione, and ascorbate in response to LL and SL treatment. Additionally, the activity of lipoxygenase and protease were increased significantly due to LL and SL treatment with a maximal increase at higher concentrations. From the present study it can be concluded that extracts of leaf and stem of A. saligna inhibit the growth of wheat and barley significantly with a concomitant increase in the functioning of the ascorbate-glutathione (AsA-GSH) cycle. Further, both crop species showed comparable responses to A. saligna leachates.

Disease development in grapefruit fruit treated with carboxymethyl chitosan (CMCS) with different induction intervals (24, 48, 72 h) at room temperature for 35 d was evaluated by disease incidence, ascorbate-glutathione cycle, cell wall metabolism, and fruit quality. The results showed that 24 h-CMCS-induction interval treatment (CIT) maintained a lower disease incidence, higher reducing substance content and better fruit firmness, compared to the control group. A 24 h-CIT treatment upregulated the expression of genes involved in signal transduction (ERF4 , ERF9 , ERF060 , ERF026 , ERF01 7 , DREB2A , DREB1D , NCED1 , MYB73 , GRXC9 and LOX2.1) and the ascorbate-glutathione cycle (AGT1 , GGCT2;2) while downregulating the expression of genes involved in cell wall degradation (XTH9 , XTH16 , PME7 and PME44). Meanwhile, 24 h-CIT treatment significantly scavenges ROS (H 2 O 2, O 2 •-), resulting in antioxidant substance (ascorbic acid, reduced glutathione) accumulation and antioxidant oxidase activity (ascorbate peroxidase, glutathione reductase, dehydroascorbate reductase and monodehydroascorbate reductase) enhancement. In addition, 24 h-CIT treatment maintained fruit firmness by inhibiting the cellular degradation enzyme activities of pectin methylesterase, polygalacturonase, cellulase and xyloglucan endotransglycosylase/hydrolase and delaying the degradation of protopectin to water-soluble pectin and ethylenediaminetetraacetic acid soluble pectin. These results demonstrated that CMCS could be used for decreasing decay occurrence and maintaining the storage quality of grapefruit fruit. • Carboxymethyl chitosan (CMCS) reduces disease incidence of grapefruit fruit. • CMCS reduces production of ROS, enhances activity of antioxidant-related enzymes. • CMCS inhibits gene expression, enzyme activities and degradation of cell wall. • CMCS modulates gene expression involved in signal transduction and AsA-GSH cycle. [ABSTRACT FROM AUTHOR]

Malus baccata Borkh., an apple rootstock, is found to be damaged by oxidation at sub-low root-zone temperature. In previous studies, we have found that exogenous sucrose could alleviate oxidative damage and increase the indole acetic acid (IAA) in roots under sub-low temperature (L). However, the role of IAA in sucrose-induced tolerance to L remains unclear. A pot experiment was conducted to evaluate the effects of exogenous sucrose and IAA synthesis/transport inhibitors (2,3,5-triiodobenzoic acid, TIBA; 4-biphenylboronic acid, BBo) on growth, IAA levels, sugars, and the antioxidant system of M. baccata under L. The results showed that the L treatment decreased IAA contents by 23.69% (48 h) and induced significant increases in root contents of malondialdehyde (MDA) and reactive oxygen (ROS), along with increasing catalase (CAT), ascorbate peroxidase (APX), and glucose-6-phosphate dehydrogenase (G6PDH) activities, while superoxide dismutase (SOD) and monodehydroascorbate reductase (MDHAR) activities first increased (24 h) and then decreased (48 h), and glutathione reductase (GR) and peroxidase (POD) activities significantly decreased. The L treatment also decreased ascorbate/oxidized ascorbate (AsA/DHA), glutathione/oxidized glutathione (GSH/GSSG), and coenzyme II/oxidized coenzyme II (NADPH/NADP+) ratios. Furthermore, the L treatment increased the contents of sucrose, fructose, glucose and sorbitol in the roots and suppressed plant growth. Sucrose pretreatment significantly increased IAA contents (12.42%, 24 h and 14.44%, 48 h) and decreased MDA and ROS contents, which improved the activities of antioxidant enzymes other than APX and increased the contents of AsA, GSH, and NADPH, and increased sucrose, fructose, and sorbitol contents and promoted plant growth. However, the sucrose + TIBA or BBo treatments decreased IAA contents and attenuated or almost abolished the positive effects of exogenous sucrose under sub-low temperature. Our findings indicate that IAA is involved in the sucrose-induced regulation of the antioxidant system in M. baccata roots under sub-low temperature and we provided theoretical references for further study on the adaptability of apple roots to low temperature.

The toxic and non-essential metalloid arsenic (As) is ubiquitous in the environment with its absorption from the soil into the plants' roots posing detrimental effects on the crop plants and hence the food availability and food security are also threatened. The present study was intended to reduce the As-induced toxicity in rice seedlings (Oryza sativa L.) by phosphate (PO43−). For this, three concentrations of potassium phosphate (KH2PO4), 50, 100 and 150 μM were supplemented along with 50 μM As exposure to hydroponically grown 7-day-old rice seedlings. Supplementation of PO43− significantly recovered arsenic-induced diminutions in growth parameters and photosynthetic pigment contents which were due to the significant increase in superoxide radical (SOR, O2•¯) and hydrogen peroxide (H2O2). Supplementation of 50 μM PO43− could significantly increase the activity of APX (ascorbate peroxidase) and GR (glutathione reductase) while 100 μM PO43− could increase the activity of DHAR (dehydroascorbate reductase) and monodehydroascorbate reductase (MDHAR). As the amount of PO43− was increased, the ratio of AsA/DHA (reduced to oxidized ascorbate) and GSH/GSSG (reduced to oxidized glutathione) was increased significantly due to increase in the reduced form of the non-enzymes i.e. AsA and GSH. The activity of SOD (superoxide dismutase) and GPX (guaiacol peroxidase) decreased significantly after a substantive increase in their activities due to As stress while the CAT (catalase) activity further enhanced after the supplementation of 50 and 100 μM PO43−. Thus, the As-induced oxidative stress in the rice seedlings was managed by concerted modulations in the activities of SOD, GPX, CAT and AsA-GSH cycle enzymes and metabolites. [ABSTRACT FROM AUTHOR]

Light‐dependent (250 or 500 µmol/m2/s, red/far‐red: 15/1; 250 µmol/m2/s and red/far‐red: 10/1) adjustment of glutathione metabolism during cold acclimation (5°C, 7 d) was compared in four wheat genotypes (14‐day‐old) differing in freezing tolerance. Only the shoot fresh weight of the two tolerant genotypes increased during cold, regardless of light conditions. Their electrolyte leakage was decreased in high light intensity. Cold greatly increased both the amount of γ‐glutamylcysteine (glutathione precursor) and cysteinylglycine (degradation product) in all genotypes grown in high intensity and far‐red lights, and consequently, the ratio of their oxidised forms exhibited a great decrease. However, cold induced a fivefold increase in the amount of glutathione and hydroxymethylglutathione disulphides only in the two sensitive genotypes grown in far‐red light. In general, the activities of the four enzymes of ascorbate–glutathione cycle were decreased by cold, except for the two tolerant genotypes cultivated in high light intensity. The gene expression studies did not reveal any transcriptional control of the changes observed at metabolite and activity levels. Our results show that both high intensity and far‐red lights are involved in the control of the cold‐induced changes in the amount/activity of the studied antioxidants, and some of these alterations have positive correlation with the level of freezing tolerance. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) is an important signaling molecule involved in mediation of salt stress induced physiological responses in plants. In this study, we investigated the effect of NO on Nitraria tangutorum seedlings exposed to salt stress. Exogenous application of NO donor, sodium nitroprusside (SNP) increased fresh weight, shoot and root elongation and decreased electrolyte leakage and malondialdehyde (MDA) content in N. tangutorum seedlings under salt stress. Simultaneously, leaf senescence and root damage induced by salt stress were alleviated. SNP effectively increased NO content both in leaves and roots of plants under salt stress. Meanwhile, SNP activated the ascorbate-glutathione (AsA-GSH) cycle by increasing antioxidants contents, antioxidant enzymes activities, and related genes expression, thereby scavenging reactive oxygen species (ROS) and alleviating oxidative damage caused by salt stress. SNP alleviated salt stress induced ion toxicity by promoting Na+ efflux and ion transporter gene expression and reducing Na+ content and the Na+/K+ ratio. In addition, application of NO specific scavenger cPTIO and mammalian NO synthase inhibitor L -NAME sifnificantly aggravated stress damage in plant under salt stress. These results show the beneficial impacts of NO as a stress-signaling molecule that positively regulates defense response in N. tangutorum to salt stress. • Sodium nitroprusside (SNP) application reduces salt-induced growth inhibition and stress damage in N. tangutorum seedlings. • SNP increases nitric oxide (NO) content both in shoots and roots. • NO alleviates salinity-induced H 2 O 2 and O 2 − generation by activating ascorbate-glutathione cycle. • NO maintains cytoplasmic Na+/K+ homeostasis by regulating ion efflux and ion transporter expression. • NO-induced changes in ROS and Na+/K+ homeostasis are positively correlated with N. tangutorum salt tolerance. [ABSTRACT FROM AUTHOR]

Injudicious usage of insecticides poses a harmful impact on non-targeted biological nitrogen fixers i.e. cyanobacteria, thereby causing substantial loss to paddy productivity. Phytohormones are emerging novel tools to optimize the adverse effect of stress factors. The current study aimed to explore the impact of insecticide cypermethrin (Cyp1; 2 μg ml−1 and Cyp2; 4 μg ml−1) on growth, protein, and exopolysaccharides (EPS) contents, oxidative stress, and ascorbate- glutathione cycle in two paddy field cyanobacteria Nostoc muscorum ATCC 27893 and Anabaena sp. PCC 7120; it also attempted to understand the regulatory role of two phytohormones: kinetin (KN, 20 nM) and indole acetic acid (IAA, 240 nM) on insecticide-induced toxicity. Insecticide at Cyp1 and Cyp2 doses diminished the growth by 10% and 30% in Anabaena sp. and by 7% and 23% in N. muscorum, respectively, and a similar reduction was documented in protein (excepts at Cyp1) and exopolysaccharides contents in both the cyanobacteria. Cypermethrin at tested doses caused cellular accumulation of oxidative biomarkers (SOR, H2O2, and MDA equivalents contents) in a concentration-dependent manner. At similar doses, the activity of AsA-GSH cycle enzymes ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), and dehydroascorbate reductase (DHAR) was stimulated (except at Cyp2 dose) while the levels of metabolites ascorbate (AsA), glutathione (GSH), AsA+DHA (dehydroascorbate) and GSH+ GSSG (oxidized GSH) and the ratios of AsA/DHA and GSH/GSSG were declined. Exogenous application of KN and IAA alleviated the toxic impact of cypermethrin as evident by a reduction in cellular accumulation of oxidative biomarkers in both the cyanobacteria by further improving the activity of enzymes (APX, MDHAR, DHAR, and GR) and the levels of metabolites (AsA, GSH, AsA+DHA, GSH+GSSH, AsA/DHA, and GSH/GSSG) of AsA-GSH cycle. The current study suggests that enhanced efficiency of the AsA-GSH cycle regulates the level of H2O2 under limit due to exogenous application of both the phytohormones, directly favoring the growth of both the cyanobacteria and this effect of KN and IAA was more pronounced in N. muscorum suggesting its resistivity against stress.

Carotenoids are photosynthetic pigments and hydrophobic antioxidants that are necessary for the survival of photosynthetic organisms, including the microalga Euglena gracilis. In the present study, we identified an uncharacterized gene encoding the E. gracilis β-carotene synthetic enzyme lycopene cyclase (EgLCY) and discovered a relationship between EgLCY-mediated carotenoid synthesis and the reactive oxygen species (ROS) scavenging system ascorbate-glutathione cycle. The EgLCY cDNA sequence was obtained via homology searching E. gracilis transcriptome data. An enzyme assay using Escherichia coli demonstrated that EgLCY converts lycopene to β-carotene. E. gracilis treated with EgLCY double-stranded RNA (dsRNA) produced colorless cells with hypertrophic appearance, inhibited growth, and marked decrease in carotenoid and chlorophyll content, suggesting that EgLCY is essential for the synthesis of β-carotene and downstream carotenoids, which are abundant and physiologically functional. In EgLCY dsRNA-treated cells, the ascorbate-glutathione cycle, composed of ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDAR), and glutathione reductase (GR), was unusually modulated; APX and GR activities significantly decreased, whereas DHAR and MDAR activities increased. Ascorbate content was significantly increased and glutathione content significantly decreased in EgLCY dsRNA-treated cells and was correlated with their recycling enzyme activities. Fluorescent imaging demonstrated that EgLCY dsRNA-treated cells accumulated higher levels of H2O2 compared to wild-type cells. Taken together, this study revealed that EgLCY-mediated synthesis of β-carotene and downstream carotenoid species upregulates APX activity and increases glutathione pool size for H2O2 scavenging. Our study suggests a possible relationship between carotenoid synthesis and the ascorbate-glutathione cycle for ROS scavenging in E. gracilis. [ABSTRACT FROM AUTHOR]

The effects of hot water treatments on antioxidant responses in red sweet pepper (Capsicum annuum L.) fruit during cold storage were investigated. Red sweet pepper fruits were treated with hot water at 55 °C for 1 (HWT-1 min), 3 (HWT-3 min), and 5 min (HWT-5 min) and stored at 10 °C for 4 weeks. The results indicated that HWT-1 min fruit showed less development of chilling injury (CI), electrolyte leakage, and weight loss. Excessive hot water treatment (3 and 5 min) caused cellular damage. Moreover, HWT-1 min slowed the production of hydrogen peroxide and malondialdehyde and promoted the ascorbate and glutathione contents for the duration of cold storage as compared to HWT-3 min, HWT-5 min, and control. HWT-1 min enhanced the ascorbate-glutathione cycle associated with ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase, but it was less effective in simulating catalase activity. Thus, HWT-1 min could induce CI tolerance in red sweet pepper fruit by activating the ascorbate-glutathione cycle via the increased activity of related enzymes and the enhanced antioxidant level. [ABSTRACT FROM AUTHOR]

Contamination of agricultural soil by chromium (Cr) is a serious menace to environmental safety and global food security. Although potential of salicylic acid (SA) in mitigating heavy metal (HM) toxicity in plants is well recognized, detailed physiological mechanisms behind such beneficial effects under Cr-stress in tomato (Solanum lycopersicum L.) plant are far from being completely unravelled. The present study evaluated the efficacy of exogenously applied SA, in alleviating Cr-mediated alterations on photosynthesis and antioxidant defense in tomato exposed to three different concentrations of Cr(VI) [0, 50, and 100 mg Cr(VI) kg−1 soil]. Exposure of tomato plants to Cr resulted in increased Cr-accumulation and oxidative damage, as signposted by high Cr concentration in root as well as shoot, augmented malondialdehyde (MDA) and superoxides levels, and inhibition in enzymes of ascorbate–glutathione (AsA-GSH) cycle. Furthermore, a significant (P ≤ 0.05) reduction in photosynthetic pigments and gas exchange parameters was also evident in Cr-stressed tomato plants. Findings of the present study showed that exogenous application of 0.5 mM SA not only promoted plant growth subjected to Cr, but also restored Cr-mediated disturbances in plant physiology. A significant (P ≤ 0.05) decrease in Cr acquisition and translocation as evidenced by improved growth and photosynthesis in SA-treated plants was observed. Additionally, exogenous SA application by virtue of its positive effect on efficient antioxidant system ameliorated the Cr-mediated oxidative stress in tomato plants as signposted by lower MDA and superoxide levels and improved AsA-GSH cycle. Overall, current study advocates the potential of exogenous SA application in amelioration of Cr-mediated physiological disturbances in tomato plant. [ABSTRACT FROM AUTHOR]

Exposure time, metal bio-accumulation, and upregulation of ascorbate-glutathione (AsA-GSH) cycle are the key factor that provide tolerance against heavy metal stress. Thus, the current study is an endeavor to prove our hypothesis that regulation of arsenate (AsV: 50, 100, and 150 mM) and arsenite (AsIII: 50, 100, and 150 μM) toxicity is time dependent (48–96 h) due to modulation in bio-accumulation pattern, AsA-GSH cycle, and non-enzymatic antioxidants in two paddy field cyanobacteria Nostoc muscorum ATCC27893 and Anabaena sp. PCC7120. After 48 h, reduction in growth associated with increased sensitivity index, As bio-accumulation, and oxidative stress was observed which further intensified after 96 h but the degree of damage was lesser than 48 h. It denotes a significant recovery in growth after 96 h which is correlated with decreased As bio-accumulation and oxidative stress due to increased efficiency of AsA-GSH cycle and non-enzymatic antioxidants. Both the species of As caused significant rise in oxidative biomarkers as evident by in -vitro analysis of O2·−, H2O2, and MDA equivalent contents despite appreciable rise in the activity antioxidative enzymes APX, DHAR, and GR. The study concludes that among both forms of arsenic, AsIII induced more toxic effect on growth by over-accumulating the ROS as evident by weak induction of AsA-GSH cycle to overcome the stress as compared to AsV. Further, with increasing the time exposure, apparent recovery was noticed with the lower doses of AsV, i.e., 50 and 100 mM and AsIII, i.e., 50 and 100 μM; however, the toxicity further aggravated with higher dose of both AsV and AsIII. Study proposes the deleterious impact of AsV and AsIII on cyanobacteria N. muscorum and Anabaena sp. but the toxicity was overcome by time-dependent recovery. [ABSTRACT FROM AUTHOR]

Durum wheat is commonly used in various food industry industries and cultivated worldwide. A serious problem with the species cultivation is its capability to accumulate cadmium (Cd) in the grains. The aim of this study is to investigate whether antioxidant activity may be used as a marker of Cd tolerance in durum wheat. The experiment involved three durum wheat genotypes/lines differing in salt tolerance. The plant response to Cd was appraised based on the activity of ascorbate–glutathione (AsA–GSH) cycle enzymes, ascorbate-to-dehydroascorbate ratio, reduced-to-oxidized glutathione ratio (GSH:GSSG), as well as Cd content in the seeds. The highest activity of dehydroascorbate reductase, monodehydroascorbate reductase, and glutathione reductase was noted in control plants of salt-sensitive cultivar “Tamaroi.” In the presence of Cd, activity of these enzymes was considerably reduced. “Tamaroi” plants demonstrated also the highest Cd content in the grain. In conclusion, we identified the cultivar “Tamaroi” as most susceptible to cadmium, and the level of durum wheat sensitivity to the element can be evaluated based on a significant decrease in the activity of AsA–GSH cycle enzymes and GSH:GSSG ratio.

The chloroplast antioxidant system in pokkali (vytilla-2), kaipad (ezhome-1) and upland (koduvelliyan) rice varieties showed upregulation of enzymatic and non- enzymatic antioxidants under salt stress. The levels of hydrogen peroxide (H2O2), malondialdehyde (MDA) with respect to the lipid peroxidation of thylakoid membrane, non-enzymatic antioxidants like ascorbate (AsA), glutathione (GSH) content, enzymatic antioxidants- superoxide dismutase (SOD) and ascorbate-glutathione cycle enzymes viz, ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR) were quantified using the isolated chloroplast fraction on the 7,14 and 21 days of NaCl treatment. Chlorophyll in the NaCl treated plants decreased concomitantly with an increase in NaCl concentration. The H2O2 content and lipid peroxidation, proportionate to MDA content and the enzymatic antioxidants of the chloroplast fraction upregulated during NaCl treatment. The specific activity of the chloroplast antioxidant and ascorbate-glutathione cycle enzymes (SOD, APX, GR, MDHAR and DHAR) showed salt dependant upregulation consistently with NaCl application. Salinity induced oxidative stress alleviation by the antioxidant system in the chloroplasts of these varieties indicate the effective cooperation between antioxidant and ascorbate-glutathione cycle enzymes and holds a vital role in combating the ROS generation, thus protecting the chloroplast in the aerobic environment.