Ascorbate-glutathione Cycle Research Articles

Physiological function and regulation of ascorbate peroxidase isoforms.

Ascorbate peroxidase (APX) reduces H2O2 to H2O by utilizing ascorbate as a specific electron donor and constitutes the ascorbate-glutathione cycle in organelles of plants including chloroplasts, cytosol, mitochondria, and peroxisomes. It has been almost 40 years since APX was discovered as an important plant-specific H2O2-scavenging enzyme, during which time many research groups have conducted molecular physiological analyses. It is now clear that APX isoforms function not only just as antioxidant enzymes but also as important factors in intracellular redox regulation through the metabolism of reactive oxygen species. The function of APX isoforms is regulated at multiple steps, from the transcriptional level to post-translational modifications of enzymes, thereby allowing them to respond flexibly to ever-changing environmental factors and physiological phenomena such as cell growth and signal transduction. In this review, we summarize the physiological functions and regulation mechanisms of expression of each APX isoform.

Desiccation tolerance in the resurrection plant Barbacenia graminifolia involves changes in redox metabolism and carotenoid oxidation.

Desiccation tolerance in vegetative tissues enables resurrection plants to remain quiescent under severe drought and rapidly recover full metabolism once water becomes available. Barbacenia graminifolia is a resurrection plant that occurs at high altitudes, typically growing on rock slits, exposed to high irradiance and limited water availability. We analyzed the levels of reactive oxygen species (ROS) and antioxidants, carotenoids and its cleavage products, and stress-related phytohormones in fully hydrated, dehydrated, and rehydrated leaves of B. graminifolia. This species exhibited a precise adjustment of its antioxidant metabolism to desiccation. Our results indicate that this adjustment is associated with enhanced carotenoid and apocarotenoids, α-tocopherol and compounds of ascorbate-glutathione cycle. While α-carotene and lutein increased in dried-leaves suggesting effective protection of the light-harvesting complexes, the decrease in β-carotene was accompanied of 10.2-fold increase in the content of β-cyclocitral, an apocarotenoid implicated in the regulation of abiotic stresses, compared to hydrated plants. The principal component analysis showed that dehydrated plants at 30 days formed a separate cluster from both hydrated and dehydrated plants for up to 15 days. This regulation might be part of the protective metabolic strategies employed by this resurrection plant to survive water scarcity in its inhospitable habitat.

Nanoselenium inhibits chromium toxicity in wheat plants by modifying the antioxidant defense system, ascorbate glutathione cycle, and glyoxalase system

Chromium (Cr) stress negatively impacts plant growth and physiological processes, making it a significant environmental concern. This study investigates the effectiveness of selenium nanoparticles (Se-NPs) in mitigating Cr stress on plants, comparing its efficacy with traditional selenium (Se). Nevertheless, research on using soil-applied Se-NP to lessen Cr buildup in plants has not been widely documented as of now. Here, we investigate the effectiveness of Se-NPs in mitigating Cr stress on plants, comparing their efficacy with traditional Se and control. Under the pervasive influence of Cr stress, Se-NPs exhibit remarkable superiority over conventional Se, significantly enhancing growth parameters (fresh weight, dry weight, shoot length, and root length), respectively, compared to the Cr-stressed plants. Physiologically, Se-NPs outperform Se by substantially improving the net photosynthesis rate (+32%), transpiration (+147%), and stomatal conductance (+64%), indicating its exceptional contribution to fortifying plant resilience under Cr stress. In mitigating oxidative stress, Se-NPs surpass Se, demonstrating a more pronounced reduction in LOX activity (−35%), MDA levels (−34%), H2O2 (−37%), and MG (−47%), showcasing heightened protection against Cr induced oxidative damage. Antioxidant defense systems also witness greater activation under Se-NPs, with higher increases in SOD (+27%), CAT (+54%), GPX (+7%), and GST (+37%) activities. Moreover, under Cr stress Se-NPs induce a more profound upregulation of antioxidant genes and the production of secondary metabolites, emphasizing its superior impact on the plant's defense mechanisms. The modulation of the ASA-GSH cycle by Se-NPs is more robust, with increased levels of ASA (+69%) and GSH (+33%), and decreased DHA (−28%) and GSSG (−29%), suggesting a more effective antioxidant network. Moreover, Se-NPs demonstrate heightened interference in Cr uptake in both root (−30%) and shoot tissues (−23%), indicating its potential to disrupt the Cr-induced ASA-GSH cycle. The study highlights the potential of Se-NPs as a more effective and sustainable approach to mitigate Cr-induced stress in plants, emphasizing the importance of understanding the underlying mechanisms and optimizing application strategies for improved agricultural sustainability and productivity in Cr-contaminated environments. Furthermore, it is necessary to conduct economic feasibility studies and assessments of the effects of Se-NP on soil microbiota in order to promote the widespread application in agricultural activities.

Transcriptome analysis reveals ABA involved in the detoxification mechanism of macroalga Gracilariopsis lemaneiformis to cadmium toxicity

IntroductionCadmium (Cd) is a significant threat environmental pollutant in the marine ecological environment offshore. The macroalga, Gracilariopsis lemaneiformis, of significant economic value, is widely cultivated along China’s coastline. Yet, little is known about the molecular mechanisms underlying Cd tolerance in macroalga.MethodsHere, we examined the transcriptome of G. lemaneiformis exposed to Cd to identify the responses to Cd stress.Results and discussionOur findings revealed that Cd led to the retardation of growth rate in G. lemaneiformis, accompanied by a notable reduction in the content of photosynthetic pigments and a decrease in the expression of genes associated with the photosynthetic system and nitrogen metabolism. When exposed to Cd, there was a rapid increase in Cd levels through the upregulation of genes encoding GlZIP6 and GlIRT1. Additionally, the expression of Cd efflux transporters, GlZIP1 and GlABCG22, and the ABCC7 transporter for compartmentation to the vacuole, was induced to mitigate Cd toxicity. Cd also activated crucial genes involved in the ABA biosynthesis and enhanced ABA content, thereby inducing ABA signaling pathway. Furthermore, exogenous ABA reduced the growth inhibition of G. lemaneiformis under Cd stress. Redox homeostasis was adjusted to adapt to Cd toxicity, with thioredoxin, glutaredoxin cycle and ascorbate-glutathione cycle identified as playing significant in maintaining reactive oxygen species homeostasis. Moreover, transcription factors such as several MYBs, signal transmission factors G protein and heat shock proteins (sHSPs, HSP 40, HSP 90, HSP101) were involved in the detoxification of Cd. Collectively, this study provided a comprehensive understanding of the molecular mechanisms underpinning the of responses of macroalga G. lemaneiformis to Cd exposure.

Nitrate reduces copper toxicity by preventing oxidative stress and inhibiting copper translocation from roots to shoots in Liriodendron Chinense.

Nitrogen forms can affect metal accumulation in plants and tolerance to metals, but a few published studies on the effects on Cu toxicity and Cu accumulation in plants are scarce. Thus, the objective of this study was to evaluate the responses of Liriodendron chinense to different nitrogen forms, by the oxidative stress, antioxidant enzymes system, GSH-AsA cycle, Cu uptake, translocation, and accumulation under Cu stress. We found that Cu-induced growth inhibiting was alleviated by added exclusive NO3--N. Adding N as NH4+-N with or without NO3--N was aggravated as evidenced by significantly elevated malonaldehyde (MDA) and hydrogen peroxide (H2O2) compared to N-Null. Cu exposure and adding NH4+-N inhibited superoxide dismutase activity, but remarkably stimulated the activities of catalase and peroxidase, the efficiency of glutathione-ascorbate (GSH-AsA) cycle, and the activity of glutathione reductase and nitrate reductase, with respect to the control. However, adding exclusive NO3--N progressively restored the alteration of antioxidant to prevent Cu-induced oxidative stress. Additionally, adding exclusive NO3--N significantly promoted the Cu uptake and accumulation in roots, but reduced Cu concentration in leaves, accompanied by the inhibited Cu translocation factor from roots to shoots by 36.7%, when compared with N-Null. Overall, adding NO3--N alleviated its Cu toxicity by preventing Cu-induced oxidative stress and inhibiting Cu translocation from roots to shoots, which provides an effective strategy for phytostabilization in Cu-contaminated lands.

The ascorbate-glutathione cycle coming of age.

Concepts regarding the operation of the ascorbate-glutathione cycle and the associated water/water cycle in the processing of metabolically generated hydrogen peroxide and other forms of reactive oxygen species (ROS) are well established in the literature. However, our knowledge of the functions of these cycles and their component enzymes continues to grow and evolve. Recent insights include participation in the intrinsic environmental and developmental signalling pathways that regulate plant growth, development, and defence. In addition to ROS processing, the enzymes of the two cycles not only support the functions of ascorbate and glutathione, they also have 'moonlighting' functions. They are subject to post-translational modifications and have an extensive interactome, particularly with other signalling proteins. In this assessment of current knowledge, we highlight the central position of the ascorbate-glutathione cycle in the network of cellular redox systems that underpin the energy-sensitive communication within the different cellular compartments and integrate plant signalling pathways.

Improving photosynthesis and the ascorbate-glutathione cycle of own-root and grafted-root chrysanthemums by brassinolide under drought stress

Improving photosynthesis and the ascorbate-glutathione cycle of own-root and grafted-root chrysanthemums by brassinolide under drought stress

Polystyrene microplastics enhanced the effect of PFOA on Chlorella sorokiniana: Perspective from the cellular and molecular levels

Microplastics (MPs) commonly coexist with other contaminants and alter their toxicity. Perfluorooctanoic acid (PFOA), an emerging pollutant, may interact with MPs but remain largely unknown about the joint toxicity of PFOA and MPs. Hence, this research explored the single and joint effects of PFOA and polystyrene microplastics (PS-MPs) on microalgae (Chlorella sorokiniana) at the cellular and molecular levels. Results demonstrated that PS-MPs increased PFOA bioavailability by altering cell membrane permeability, thus aggravating biotoxicity (synergistic effect). Meanwhile, the defense mechanisms (antioxidant system modulation and extracellular polymeric substances secretion) of Chlorella sorokiniana were activated to alleviate toxicity. Additionally, transcriptomic analysis illustrated that co-exposure had more differential expression genes (DEGs; 4379 DEGs) than single-exposure (PFOA: 2533 DEGs; PS-MPs: 492 DEGs), which were mainly distributed in the GO terms associated with the membrane composition and antioxidant system. The molecular regulatory network further revealed that PS-MPs and PFOA primarily regulated the response mechanisms of Chlorella sorokiniana by altering the ribosome biogenesis, photosynthesis, citrate cycle, oxidative stress, and antioxidant system (antioxidant enzyme, glutathione-ascorbate cycle). These findings elucidated that PS-MPs enhanced the effect of PFOA, providing new insights into the influences of MPs and PFOA on algae and the risk assessment of multiple contaminants. Environmental implicationMPs and PFAS, emerging contaminants, are difficult to degrade and pose a non-negligible threat to organisms. Co-pollution of MPs and PFAS is ubiquitous in the aquatic environment, while risks of co-existence to organisms remain unknown. The present study revealed the toxicity and defense mechanisms of microalgae exposure to PS-MPs and PFOA from cellular and molecular levels. According to biochemical and transcriptomic analyses, PS-MPs increased PFOA bioavailability and enhanced the effect of PFOA on Chlorella sorokiniana, showing a synergistic effect. This research provides a basis for assessing the eco-environmental risks of MPs and PFAS.

Modification in the ascorbate-glutathione cycle leads to a better acclimation to high light in the rose Bengal resistant mutant of Nannochloropsis oceanica

Understanding how to adapt outdoor cultures of Nannochloropsis oceanica to high light (HL) is vital for boosting productivity. The N. oceanica RB2 mutant, obtained via ethyl methanesulfonate mutagenesis, was chosen for its tolerance to Rose Bengal (RB), a singlet oxygen (1O2) generator. Compared to the wild type (WT), the RB2 mutant showed higher resilience to excess light conditions. Analyzing the ascorbate-glutathione cycle (AGC), involving ascorbate peroxidases (APX, EC 1.11.1.11), dehydroascorbate reductase (DHAR, EC 1.8.5.1), and glutathione reductase (GR, EC 1.8.1.7), in the RB2 mutant under HL stress provided valuable insights. At 250 μmol photon m−2 s−1 (HL), the WT strain displayed superoxide anion radicals (O2▪-) and hydrogen peroxide (H2O2) accumulation, increased lipid peroxidation, and cell death compared to normal light (NL) conditions (50 μmol photon m−2 s−1). The RB2 mutant didn't accumulate O2▪- and H2O2 after HL exposure, and exhibited increased APX, DHAR, and GR activities and transcript levels compared to WT and remained consistent after HL treatment. Although the RB2 mutant had a smaller ascorbate (AsA) pool than the WT, its ability to regenerate dehydroascorbate (DHA) increased post HL exposure, indicated by a higher AsA/DHA ratio. Additionally, under HL conditions, the RB2 mutant displayed an improved glutathione (GSH) regeneration rate (GSH/GSSG ratio) without changing the GSH pool size. Remarkably, H2O2 or menadione (a O2▪- donor) treatment induced cell death in the WT strain but not in the RB2 mutant. These findings emphasize the essential role of AGC in the RB2 mutant of Nannochloropsis in handling photo-oxidative stress.

Coordination of elicitors and ascorbate-glutathione cycle: A vital nexus for mitigating post-harvest injury and losses of cultivated fruits

Fruit losses and waste are predominantly caused by postharvest diseases, with their management traditionally reliant on pesticides. The extensive utilisation of synthetic fungicides can cause harmful impacts on both human health and the environment, necessitating a reduction in their use. Recent advancements have led to the development of novel, benign strategies using natural or biologically derived compounds. These compounds, known as 'elicitors,' have the strength to instigate the plant's defence mechanism, enhancing the fruit’s resilience counter to future stress and reducing postharvest spoilage. In recent years, the impact of the plant defence system concerning elicitor compounds has been measurable through physiological parameters or the enzymatic activity of molecular markers. Antioxidant activity, a crucial parameter to determine fruit quality and tolerance to biotic and abiotic stresses, significantly functions in stress response and maintaining postharvest quality. Elicitors can prompt endurance in fruits instead of diverse environmental stresses by promoting the biosynthesis of antioxidant components and enhancing antioxidant capability through the ascorbate-glutathione (AsA-GSH) cycle. Recent findings have exhibited that applying chemical elicitors can enhance antioxidant activity by augmenting the content of AsA and GSH and by regulating the redox stability, thereby maintaining quality in harvested fruits. This review summarises recent findings demonstrating how elicitor sprays enrich antioxidant activity in harvested fruits by accelerating the synthesis of antioxidants and defence components. This provides insight into fruit defence mechanisms induced under various elicitors and their prospects in postharvest biology.

Integrated physiological and metabolomic responses reveal mechanisms of Cd tolerance and detoxification in kenaf (Hibiscus cannabinus L.) under Cd stress.

Cadmium (Cd) is a highly toxic trace element that occurs in large quantities in agricultural soils. The cultivation of industrial crops with high phytoremediation potential, such as kenaf, could effectively reduce soil Cd contamination, but the mechanisms of toxicity, tolerance, and detoxification remain unclear. In this study, the effects of different Cd concentrations (0, 100, 250, and 400 µM) on growth, biomass, Cd uptake, physiological parameters, metabolites and gene expression response of kenaf were investigated in a hydroponic experiment. The results showed that Cd stress significantly altered the ability of kenaf to accumulate and transport Cd; increased the activity of hydrogen peroxide (H2O2), superoxide anion (O2 -), and malondialdehyde (MDA); reduced the activities of superoxide dismutase (SOD) and catalase (CAT); and decreased the content of photosynthetic pigments, resulting in significant changes in growth and biomass production. Exposure to Cd was found to have a detrimental effect on the ascorbate-glutathione (AsA-GSH) cycle in the roots, whereas it resulted in an elevation in AsA levels and a reduction in GSH levels in the leaves. The increased content of cell wall polysaccharides under Cd stress could contribute to Cd retention in roots and limited Cd transport to above-ground plant tissues. Metabolomic analyses revealed that alanine, aspartate, and glutamate metabolism, oxidative phosphorylation, ABC transporter, and carbon metabolism were the major metabolic pathways associated with Cd stress tolerance. Cd stress increased gene expression of IRT1 and MTP1 in roots, which resulted in kenaf roots accumulating high Cd concentrations. This study extends our knowledge of the factors regulating the response of kenaf to Cd stress. This work provided a physiological and metabolomic perspective on the mechanism controlling the response of kenaf to Cd stress.

Mepiquat chloride priming confers the ability of cotton seed to tolerate salt by promoting ABA-operated GABA signaling control of the ascorbate–glutathione cycle

BackgroundEnsuring that seeds germinate and emerge normally is a prerequisite for cotton production, esp. in areas with salinized soil. Priming with mepiquat chloride (MC) can promote seed germination and root growth under salt stress, but its mechanism has not been fully elucidated. In this study, physiological and biochemical experiments revealed that MC-priming promotes the tolerance of cotton seeds to salt stress by increasing the ability of antioxidant enzymes related to the ascorbate–glutathione (AsA-GSH) cycle to scavenge reactive oxygen species (ROS).ResultsResults revealed that treatment with inhibitors of abscisic acid (ABA) and γ-aminobutyric acid (GABA) biosynthesis reduced the positive effects of MC-priming. Similarly, MC-priming increased the contents of ABA and GABA under salt stress by stimulating the expression levels of GhNCED2 and GhGAD4 and the activity of calmodulin-binding (CML) glutamate decarboxylase (GAD). Further analysis showed that an inhibitor of ABA synthesis reduced the positive impacts of MC-priming on the content of GABA under salt stress, but the content of ABA was not affected by the GABA synthesis inhibitor. Furthermore, a multi-omics analysis revealed that MC-priming increased the abundance and phosphorylation levels of the proteins related to ABA signaling, CML, and Ca2+ channels/transporters in the MC-primed treatments, which resulted in increased oscillations in Ca2+ in the MC-primed cotton seeds under salt stress.ConclusionIn summary, these results demonstrate that MC-mediated ABA signaling operates upstream of the GABA synthesis generated by GAD by activating the oscillations of Ca2+ and then enhancing activity of the AsA-GSH cycle, which ensures that cotton seeds are tolerant to salt stress.

Nickel Ions Enhanced the Adaptability of Tomato Seedling Roots to Low-Nitrogen Stress by Improving Their Antioxidant Capacity

To elucidate the physiological mechanisms underlying the impact of exogenous nickel ions (Ni2+) on the adaptability of tomato (Solanum lycopersicum L.) seedling roots to low-nitrogen levels, the cultivar ‘Micro Tom’ was selected as the experimental material and cultivated hydroponically in the cultivation room of the Fujian Agriculture and Forestry University. Two distinct nitrogen concentrations (7.66 and 0.383 mmol·L−1) and two different levels of Ni2+ (0 and 0.1 mg·L−1 of NiSO4·6H2O) were employed as treatments. On the 9th day of cultivation, we measured the root biomass, the concentrations of antioxidant compounds, and the activities of antioxidant enzymes in the tomato seedlings. The study showed that when the nitrogen levels were low, the growth and development of the tomato seedling roots were hindered. This led to a significant increase in the levels of hydrogen peroxide (H2O2), superoxide anion (O2−), and malondialdehyde (MDA), indicating oxidative damage to the roots. Conversely, treatment with Ni2+ induced a notable increase in the activity of antioxidant enzymes in the seedlings and augmented the accumulation of nonenzymatic antioxidants, such as ascorbic acid (ASA) and reduced glutathione (GSH), thereby enhancing the operational efficiency of the ascorbate–glutathione cycle (ASA–GSH). Consequently, this led to substantial reductions in the H2O2 and MDA levels, ultimately mitigating the oxidative damage inflicted on the tomato seedling roots subjected to low-nitrogen stress. In conclusion, exogenous Ni2+ can reduce the peroxidative damage of tomato seedlings by promoting antioxidase activity in tomato seedlings under low-nitrogen stress, improve the tolerance of tomato seedlings to low-nitrogen stress, and maintain the normal growth and development of tomato seedlings.

Phenomic profiling to reveal tolerance mechanisms and regulation of ascorbate-glutathione cycle in wheat varieties (Triticum aestivum L.) under arsenic stress.

The potential of arsenic (As) tolerant and sensitive varieties of wheat (Triticum aestivum L.) has yet to be explored despite of alarming situation of arsenic toxicity. To fill this gap, the study aimed to explore the role of antioxidants, phytochelatins, and ascorbate-glutathione for As tolerance in wheat. A total of eight varieties were exposed to different arsenate treatments (0, 1, 5, 10, 50, 100, 200, 500, 1000, 2000, and 10,000μM) initially to screen effective treatment as well as contrasting varieties via Weibull distribution frequency for further analysis. The Weibull analysis found 200μM as the most effective treatment in the present study. Selected varieties were analyzed for accumulation of total As and As speciation, oxidative stress (malondialdehyde, hydrogen peroxide), antioxidants (superoxide dismutase, catalase, peroxidase), phytochelatins, and ascorbate-glutathione cycle (glutathione-S-transferase, glutathione reductase, glutathione peroxidase, ascorbate peroxidase). Tolerant varieties showed less accumulation and translocation of total As, arsenate, and arsenite to the shoots compared with sensitive varieties under 200μM treatment. Low concentration in tolerant varieties correlated with better growth and development response. Tolerant varieties showed higher induction of metabolites (glutathione, phytochelatins) compared to sensitive ones. Furthermore, tolerant varieties showed better performance of antioxidant and ascorbate-glutathione cycle enzymes in response to As exposure. The findings of the present study provided great insight into the wheat tolerance mechanism upon As exposure between contrasting varieties.

The physiological responses of celery (Apium graveolens L.) and its ability to accumulate selenium when inoculated with Funneliformis mosseae

Celery (Apium graveolens L.) has a strong capacity to enrich selenium (Se) and is a good system for research on Se enrichment in vegetables. Arbuscular mycorrhizal fungi (AMF) are commonly used plant symbionts that affect plant growth and their effectiveness is plant species specific. However, there is little research on the effects of AMF inoculation on the accumulation and translocation of Se in celery. The treatments in this study included inoculation with AMF (+AMF) and the application of different types and concentrations of exogenous Se. We evaluated the growth, root mycorrhizal colonization, photosynthetic pigment content, ascorbate-glutathione cycle (ASA-GSH cycle), the accumulation and translocation of Se and the combination of AMF + Se compared with an untreated control. The application of low concentrations of Se (≤10 mg kg−1) stimulated celery growth, while high concentrations (>20 mg kg−1) had the opposite effect. The inhibition of celery growth was more severe with Se6+ than Se4+ when applied at the same concentration. The accumulation of Se improved in all the organs of celery as the supply increased. AMF had a significant positive effect on the accumulation and translocation of Se. In addition, +AMF significantly increased the shoot height and root fresh weight of celery and reduced the inhibitory effect of Se on growth. However, +AMF had slight effects on the levels of photosynthetic pigments and the ASA-GSH cycle. +AMF combined with 10 mg kg−1 sodium selenite (Se4+) is an effective way to produce Se-rich celery.

Cytokinin and indole-3-acetic acid crosstalk is indispensable for silicon mediated chromium stress tolerance in roots of wheat seedlings

The rising heavy metal contamination of soils imposes toxic impacts on plants as well as other life forms. One such highly toxic and carcinogenic heavy metal is hexavalent chromium [Cr(VI)] that has been reported to prominently retard the plant growth. The present study investigated the potential of silicon (Si, 10 µM) to alleviate the toxicity of Cr(VI) (25 µM) on roots of wheat (Triticum aestivum L.) seedlings. Application of Si to Cr(VI)-stressed wheat seedlings improved their overall growth parameters. This study also reveals the involvement of two phytohormones, namely auxin and cytokinin and their crosstalk in Si-mediated mitigation of the toxic impacts of Cr(VI) in wheat seedlings. The application of cytokinin alone to wheat seedlings under Cr(VI) stress reduced the intensity of toxic effects of Cr(VI). In combination with Si, cytokinin application to Cr(VI)-stressed wheat seedlings significantly minimized the decrease induced by Cr(VI) in different parameters such as root-shoot length (10.8% and 13%, respectively), root-shoot fresh mass (11.3% and 10.1%, respectively), and total chlorophyll and carotenoids content (13.4% and 6.8%, respectively) with respect to the control. This treatment also maintained the regulation of proline metabolism (proline content, and P5CS and PDH activities), ascorbate-glutathione (AsA-GSH) cycle and nutrient homeostasis. The protective effect of Si and cytokinin against Cr(VI) stress was minimized upon supplementation of an inhibitor of polar auxin transport- 2,3,5-triiodobenzoic acid (TIBA) which suggested a potential involvement of auxin in Si and cytokinin-mediated mitigation of Cr(VI) toxicity. The exogenous addition of a natural auxin – indole-3-acetic acid (IAA) confirmed auxin is an active member of a signaling cascade along with cytokinin that aids in Si-mediated Cr(VI) toxicity alleviation as IAA application reversed the negative impacts of TIBA on wheat roots treated with Cr(VI), cytokinin and Si. The results of this research are also confirmed by the gene expression analysis conducted for nutrient transporters (Lsi1, CCaMK, MHX, SULT1 and ZIP1) and enzymes involved in the AsA-GSH cycle (APX, GR, DHAR and MDHAR). The overall results of this research indicate towards possible induction of a crosstalk between cytokinin and IAA upon Si supplementation which in turn stimulates physiological, biochemical and molecular changes to exhibit protective effects against Cr(VI) stress. Further, the information obtained suggests probable employment of Si, cytokinin and IAA alone or combined in agriculture to maintain plant productivity under Cr(VI) stress and data regarding expression of key genes can be used to develop new crop varieties with enhanced resistance against Cr(VI) stress together with its reduced load in seedlings.

The combination of high oxygen and nanocomposite packaging alleviated quality deterioration by promoting antioxidant capacity and phenylpropane metabolism in Volvariella volvacea

Volvariella volvacea is a highly perishable mushroom that severely affects its postharvest commercial value. This study aimed to investigate the impact of high oxygen (O2) levels combined with nanocomposite packaging on the shelf-life quality of V. volvacea. Results showed that treatment with high concentrations of O2 (80% and 100% O2) and nanocomposite packaging effectively delayed the quality deterioration of V. volvacea, resulting in better postharvest appearance, higher firmness, lower weight loss, malondialdehyde (MDA) content, and leakage of membrane electrolytes. Further analysis revealed the combination treatments ameliorated oxidative stress by inducing antioxidant enzymes and the glutathione-ascorbate (GSH-AsA) cycle at both enzymatic and transcriptional levels, thereby activating the antioxidant system. Additionally, the treatments enhanced activities of key enzymes in phenylpropane metabolism, leading to a reduction in the decrease of total phenolics and flavonoids. This work provides new insights into the development of postharvest technologies to prolong the storage life of V. volvacea.

High-Proportion Blue Light Irradiation at the End-of-Production Stage Promotes the Biosynthesis and Recycling of Ascorbate in Lettuce.

Ascorbate (AsA), an essential antioxidant for both plants and the human body, plays a vital role in maintaining proper functionality. Light plays an important role in metabolism of AsA in horticultural plants. Our previous research has revealed that subjecting lettuce to high light irradiation (HLI) (500 μmol·m-2·s-1) at the end-of-production (EOP) stage effectively enhances AsA levels, while the optimal light quality for AsA accumulation is still unknown. In this study, four combinations of red (R) and blue (B) light spectra with the ratio of 1:1 (1R1B), 2:1 (2R1B), 3:1 (3R1B), and 4:1 (4R1B) were applied to investigate the biosynthesis and recycling of AsA in lettuce. The results demonstrated that the AsA/total-AsA content in lettuce leaves was notably augmented upon exposure to 1R1B and 2R1B. Interestingly, AsA levels across all treatments increased rapidly at the early stage (2-8 h) of irradiation, while they increased slowly at the late stage (8-16 h). The activity of L-galactono-1,4-lactone dehydrogenase was augmented under 1R1B treatment, which is pivotal to AsA production. Additionally, the activities of enzymes key to AsA cycling were enhanced by 1R1B and 2R1B treatments, including ascorbate peroxidase, dehydroascorbate reductase, and monodehydroascorbate reductase. Notably, hydrogen peroxide and malondialdehyde accumulation increased dramatically following 16 h of 1R1B and 2R1B treatments. In addition, although soluble sugar and starch contents were enhanced by EOP-HLI, this effect was comparatively subdued under the 1R1B treatment. Overall, these results indicated that AsA accumulation was improved by irradiation with a blue light proportion of over 50% in lettuce, aligning with the heightened activities of key enzymes responsible for AsA synthesis, as well as the accrual of hydrogen peroxide. The effective strategy holds the potential to enhance the nutritional quality of lettuce while bolstering its antioxidant defenses.

Attenuation of prochloraz phytotoxicity to postharvest mango fruit by melatonin is associated with the regulation of detoxification capacity

Excessive fungicide residues in crops threaten food safety, and may initiate oxidative stress and cause phytotoxicity to products. Melatonin (Mel), a pleiotropic bioactive molecule, plays multiple physiological functions in plants. In this study, utilizing postharvest dipping with Mel and fungicide prochloraz (Pcz) as the model, we explored the effect of Mel on Pcz-triggered toxification and its underlying physiological mechanism in ‘Guifei’ mango fruit during storage at 25 °C. Results showed that pretreatment with 1 mmol L−1 Mel before exposure to 1.2 g L−1 Pcz (Mel + Pcz) reduced Pcz residues by 15.1% and 30.7% in mango fruit at 4 and 8 d, respectively, while ameliorating phytotoxicity to a greater extent than Pcz treatment alone. Microscopic observation revealed that Mel alleviated Pcz-triggered damage to lenticels on fruit exocarp tissue. Mel appreciably repressed Pcz-induced oxidative stress, as indicated by lower levels of reactive oxygen species, malondialdehyde, damaged DNA and carbonylated proteins and good maintenance of membrane integrity and mitochondrial membrane potential in Mel + Pcz fruit. Moreover, Pcz-induced increases in activities of antioxidant enzymes (superoxide dismutase, catalase and peroxidase), levels of ascorbate-glutathione cycle components and activities of pesticide degradative enzymes (cytochrome P450, glutathione S-transferase and glycosyltransferase) were further amplified after treatment with Mel + Pcz, which contributed to a stronger detoxification capacity in mango fruit. The study might provide a strategy for diminishing fungicide residues and attenuating phytotoxicity in postharvest fruits.

Mechanism of selenite tolerance during barley germination: A combination of tissue selenium metabolism alterations and ascorbate-glutathione cycle modulation

Selenite is widely used to increase Selenium (Se) content in cereals, however excessive selenite may be toxic to plant growth. In this study, barley was malted to elucidate the action mechanism of selenite in the generation and detoxification of oxidative toxicity. The results showed that high doses (600 μM) of selenite radically increased oxidative stress by the elevated accumulation of superoxide and malondialdehyde, leading to phenotypic symptoms of selenite-induced toxicity like stunted growth. Barley tolerates selenite through a combination of mechanisms, including altering Se distribution in barley, accelerating Se efflux, and increasing the activity of some essential antioxidant enzymes. Low doses (150 μM) of selenite improved barley biomass, respiratory rate, root vigor, and maintained the steady-state equilibrium between reactive oxygen species (ROS) and antioxidant enzyme. Selenite-induced proline may act as a biosignal to mediate the response of barley to Se stress. Furthermore, low doses of selenite increased the glutathione (GSH) and ascorbate (AsA) concentrations by mediating the ascorbate-glutathione cycle (AsA-GSH cycle). GSH intervention and dimethyl selenide volatilization appear to be the primary mechanisms of selenite tolerance in barley. Thus, results from this study will provide a better understanding of the mechanisms of selenite tolerance in crops.