The cellular redox state in plant stress biology--a charging concept

Evaluating micro-nano bubbles coupled with rice-crayfish co-culture systems: A field study promoting sustainable rice production intensification

Traditional rice-fish symbiosis systems efficiently use soil and water resources but the adverse effects of prolonged flooding on the stability of rice growth can be mitigated. The feasibility and efficacy of injecting micro-nano bubbles (MNBs) in rice-crayfish co-cultures was investigated in a 22-hectare field experiment conducted over five months. This injection significantly enhanced the growth of both rice and crayfish, and increased total nitrogen and phosphorus levels in the soil, thereby augmenting fertility. Analysis of dissolved oxygen (DO), water temperature and gene expression (rice and crayfish) clarified that micro-nano bubbles (MNBs) foster an optimal environment for rice root respiration, whereas rice establishes an optimal temperature for crayfish, thereby enhancing their activity and growth. Comparative analyses of gene expression profiles and metabolic pathway enrichment revealed that the injection of MNBs diversifies soil microbial communities and intensifies biological processes, such as plant hormone signal transduction. This was in marked contrast to the situation in our controls, rice monoculture (R) and micro-nano bubbles rice monoculture (MNB-R). The combination of rice-fish symbiosis with MNBs led to a 26.8 % increase in rice production and to an estimated 35 % improvement in economic efficiency. Overall, this research introduces an innovative and environmentally sustainable method to boost rice yields, thereby enhancing food security and providing additional income for farmers.

Veterinary antibiotics differ in phytotoxicity on oilseed rape grown over a wide range of concentrations

Residues of veterinary antibiotics are a worldwide problem of increasing concern due to their persistence and diverse negative effects on organisms, including crops, and limited understanding of their phytotoxicity. Therefore, this study aimed to compare the phytotoxic effects of veterinary antibiotics tetracycline (TC) and ciprofloxacin (CIP) applied in a wide range of concentrations on model plant oilseed rape (Brassica napus). Overall phytotoxicity of 1-500 mg kg-1 of TC and CIP was investigated based on morphological, biochemical, and physiological plant response. Photosystem II (PSII) performance was suppressed by TC even under environmentally relevant concentration (1 mg kg-1), with an increasing effect proportionally to TC concentration in soil. In contrast, CIP was found to be more phytotoxic than TC when applied at high concentrations, inducing a powerful oxidative burst, impairment of photosynthetic performance, collapse of antioxidative protection and sugar metabolism, and in turn, complete growth retardation at 250 and 500 mg kg-1 CIP treatments. Results of our study suggest that TC and CIP pollution do not pose a significant risk to oilseed rapes in many little anthropogenically affected agro-environments where TC or CIP concentrations do not exceed 1 mg kg-1; however, intensive application of manure with high CIP concentrations (more than 50 mg kg-1) might be detrimental to plants and, in turn, lead to diminished agricultural production and a potential risk to human health.

Comprehensive transcriptome analyses of Fusarium-infected root xylem tissues to decipher genes involved in chickpea wilt resistance

Fusarium wilt is the most destructive soil-borne disease that poses a major threat to chickpea production. To comprehensively understand the interaction between chickpea and Fusarium oxysporum, the xylem-specific transcriptome analysis of wilt-resistant (WR315) and wilt-susceptible (JG62) genotypes at an early timepoint (4DPI) was investigated. Differential expression analysis showed that 1368 and 348 DEGs responded to pathogen infection in resistant and susceptible genotypes, respectively. Both genotypes showed transcriptional reprogramming in response to Foc2, but the responses in WR315 were more severe than in JG62. Results of the KEGG pathway analysis revealed that most of the DEGS in both genotypes with enrichment in metabolic pathways, secondary metabolite biosynthesis, plant hormone signal transduction, and carbon metabolism. Genes associated with defense-related metabolites synthesis such as thaumatin-like protein 1b, cysteine-rich receptor-like protein kinases, MLP-like proteins, polygalacturonase inhibitor 2-like, ethylene-responsive transcription factors, glycine-rich cell wall structural protein-like, beta-galactosidase-like, subtilisin-like protease, thioredoxin-like protein, chitin elicitor receptor kinase-like, proline transporter-like, non-specific lipid transfer protein and sugar transporter were mostly up-regulated in resistant as compared to susceptible genotypes. The results of this study provide disease resistance genes, which would be helpful in understanding the Foc resistance mechanism in chickpea.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03803-9.

Overexpression of Grapevine VyTRXy Improves Drought Tolerance by Maintaining Photosynthesis and Enhancing the Antioxidant and Osmolyte Capacity of Plants

Drought stress profoundly affects plant growth and development, posing a significant challenge that is extensively researched in the field. Thioredoxins (TRXs), small proteins central to redox processes, are crucial to managing both abiotic and biotic stresses. In this research, the VyTRXy gene, cloned from wild Yanshan grapes, was validated as a functional TRX through enzyme activity assays. VyTRXy was found to bolster photosynthesis, augment levels of osmotic regulators, stimulate antioxidant enzyme activities, and strengthen drought resilience in transgenic plants. These enhancements were evidenced by higher survival rates, optimized photosynthetic metrics, increased proline levels, augmented chlorophyll concentration, reduced electrolyte leakage, and decreased malondialdehyde and hydrogen peroxide (H2O2) levels. Furthermore, there was a surge in the activities of enzymes such as catalase, ascorbate peroxidase, glutathione peroxidase, dehydroascorbate reductase, and glutathione reductase, along with an increased expression of TRX peroxidase. Notably, under drought stress, there was a marked elevation in the expression of stress-responsive genes, including the adversity stress-inducible expression gene (NtRD29A) and DRE-binding protein (NtDREB), in transgenic tobacco. This investigation is pivotal in the quest for drought-resistant grapevine varieties and provides significant insights into the molecular functionality of VyTRXy in enhancing grapevine drought tolerance.

Drought Stress Tolerance in Vegetables: The Functional Role of Structural Features, Key Gene Pathways, and Exogenous Hormones

The deleterious effects of drought stress have led to a significant decline in vegetable production, ultimately affecting food security. After sensing drought stress signals, vegetables prompt multifaceted response measures, eventually leading to changes in internal cell structure and external morphology. Among them, it is important to highlight that the changes, including changes in physiological metabolism, signal transduction, key genes, and hormone regulation, significantly influence drought stress tolerance in vegetables. This article elaborates on vegetable stress tolerance, focusing on structural adaptations, key genes, drought stress signaling transduction pathways, osmotic adjustments, and antioxidants. At the same time, the mechanisms of exogenous hormones such as abscisic acid (ABA), jasmonic acid (JA), salicylic acid (SA), and ethylene (ET) toward improving the adaptive drought tolerance of vegetables were also reviewed. These insights can enhance the understanding of vegetable drought tolerance, supporting vegetable tolerance enhancement by cultivation technology improvements under changing climatic conditions, which provides theoretical support and technical reference for innovative vegetable stress tolerance breeding and food security.

GsNAC2 gene enhances saline-alkali stress tolerance by promoting plant growth and regulating glutathione metabolism in Sorghum bicolor

The quality and yields of Sorghum bicolo r plants are seriously affected by saline-alkali conditions. NAC (NAM, ATAF, and CUC) transcription factors are plant specific and have various functions in plant development and response to various stresses. To investigate how GsNAC2 functions in sorghum responses to saline-alkali treatment, the characteristics of GsNAC2 were analysed by bioinformatics methods, and NaHCO3 :Na2 CO3 (5:1, 75mM, pH 9.63) saline-alkali stress solution was applied when sorghum plants were 2weeks old. The research results show that GsNAC2 belongs to the NAC gene family. GsNAC2 was significantly induced by saline-alkali treatment and strongly expressed in sorghum leaves. GsNAC2 -overexpressing sorghum plants had increased plant height, dry weight, moisture content, root activity, leaf length, chlorophyll content, stomatal conductance, relative root activity, relative chlorophyll content, relative stomatal conductance, and relative transpiration rate after saline-alkali treatment. Lower H2 O2 and O2 - levels, relative permeability of the plasma membrane, and malondialdehyde (MDA) content were found in GsNAC2 -overexpressing sorghum. In transcriptome analysis, clusters of orthologous groups (COG) analysis showed that a high proportion of differentially-expressed genes (DEGs) participated in defence mechanisms at each processing time, and 18 DEGs related to synthetic glutathione were obtained. Gene expression analysis revealed that key genes in glutathione biosynthesis pathways were upregulated. GR and GSH-Px activities were increased, and GSH accumulated more with the overexpression of GsNAC2 after saline-alkali treatment. Furthermore, these results suggest that GsNAC2 acts as a potentially important regulator in response to saline-alkali stress and may be used in molecular breeding to improve crop yields under adverse environmental conditions.

Glutathione Transferases Are Involved in the Genotype-Specific Salt-Stress Response of Tomato Plants

Glutathione transferases (GSTs) are one of the most versatile multigenic enzyme superfamilies. In our experiments, the involvement of the genotype-specific induction of GST genes and glutathione- or redox-related genes in pathways regulating salt-stress tolerance was examined in tomato cultivars (Solanum lycopersicum Moneymaker, Mobil, and Elán F1). The growth of the Mobil plants was adversely affected during salt stress (100 mM of NaCl), which might be the result of lowered glutathione and ascorbate levels, a more positive glutathione redox potential (EGSH), and reduced glutathione reductase (GR) and GST activities. In contrast, the Moneymaker and Elán F1 cultivars were able to restore their growth and exhibited higher GR and inducible GST activities, as well as elevated, non-enzymatic antioxidant levels, indicating their enhanced salt tolerance. Furthermore, the expression patterns of GR, selected GST, and transcription factor genes differed significantly among the three cultivars, highlighting the distinct regulatory mechanisms of the tomato genotypes during salt stress. The correlations between EGSH and gene expression data revealed several robust, cultivar-specific associations, underscoring the complexity of the stress response mechanism in tomatoes. Our results support the cultivar-specific roles of distinct GST genes during the salt-stress response, which, along with WRKY3, WRKY72, DREB1, and DREB2, are important players in shaping the redox status and the development of a more efficient stress tolerance in tomatoes.

Modifications in Ultrastructural Characteristics and Redox Status of Plants under Environmental Stress: A Review

The rate of global environmental change is unprecedented, with climate change causing an increase in the oscillation and intensification of various abiotic stress factors that have negative impacts on crop production. This issue has become an alarming global concern, especially for countries already facing the threat of food insecurity. Abiotic stressors, such as drought, salinity, extreme temperatures, and metal (nanoparticle) toxicities, are recognized as major constraints in agriculture, and are closely associated with the crop yield penalty and losses in food supply. In order to combat abiotic stress, it is important to understand how plant organs adapt to changing conditions, as this can help produce more stress-resistant or stress-tolerant plants. The investigation of plant tissue ultrastructure and subcellular components can provide valuable insights into plant responses to abiotic stress-related stimuli. In particular, the columella cells (statocytes) of the root cap exhibit a unique architecture that is easily recognizable under a transmission electron microscope, making them a useful experimental model for ultrastructural observations. In combination with the assessment of plant oxidative/antioxidative status, both approaches can shed more light on the cellular and molecular mechanisms involved in plant adaptation to environmental cues. This review summarizes life-threatening factors of the changing environment that lead to stress-related damage to plants, with an emphasis on their subcellular components. Additionally, selected plant responses to such conditions in the context of their ability to adapt and survive in a challenging environment are also described.

Exposure to metals and the disruption of sex hormones in 6-19 years old children: An exploration of mixture effects

BACKGROUND

Individual metals have been linked to sex hormones disruption, but the associations of metals mixture are rarely examined among children.

METHODS

A total of 1060 participants of 6-19-year-old who participated in the National Health and Nutrition Examination Survey (2013-2016) were included. Eighteen metals were quantified in the whole blood and urine. Sex hormones were measured in serum, including total testosterone (TT), estradiol (E₂), and sex hormone binding globulin (SHBG). In addition, free androgen index (FAI) and the ratio of TT to E₂ were calculated. Bayesian kernel machine regression and latent class analysis were performed to assess the associations of metals mixture and exposure patterns of metals at varied levels with sex hormones while adjusting for selected covariates. All analyses were conducted by sex-age and sex-puberty groups to explore the potential sex-dimorphic effects.

RESULTS

Exposure to metals mixture was associated with elevated levels of FAI and E₂ among 12-19 years old girls. Moreover, the exposure pattern of metals that was characterized by high levels of blood and urinary cadmium, blood manganese, and urinary cobalt was associated with elevated E₂ and reduced TT/E₂ levels among girls of 12-19 years old. However, the associations of metals mixture with sex hormones were overall nonsignificant among boys. Nevertheless, metals exposure pattern that was characterized by high levels of blood lead, urinary barium, strontium, and lead but comparatively low levels of the other metals was consistently associated with reduced levels of FAI and E₂ but elevated levels of TT/E₂ and SHBG among boys of 12-19 years old.

CONCLUSION

Metals mixture and exposure patterns that were dominated by high levels of certain metals were associated with sex hormones imbalance among 12-19 years old children in a sex-dimorphic pattern, with the identified individual metals that drove the associations of metals mixture varied by sex.

Primary root response to combined drought and heat stress is regulated via salicylic acid metabolism in maize

The primary root is the first organ to perceive the stress signals for abiotic stress. In this study, maize plants subjected to drought, heat and combined stresses displayed a significantly reduced primary root length. Metabolic and transcriptional analyses detected 72 and 5,469 differentially expressed metabolites and genes in response to stress conditions, respectively. The functional annotation of differentially expressed metabolites and genes indicated that primary root development was mediated by pathways involving phenylalanine metabolism, hormone metabolism and signaling under stress conditions. Furthermore, we found that the concentration of salicylic acid and two precursors, shikimic acid and phenylalanine, showed rapid negative accumulation after all three stresses. The expression levels of some key genes involved in salicylic acid metabolism and signal transduction were differentially expressed under stress conditions. This study extends our understanding of the mechanism of primary root responses to abiotic stress tolerance in maize.

Exogenous proline mitigates toxic effects of cadmium via the decrease of cadmium accumulation and reestablishment of redox homeostasis in Brassica juncea

BACKGROUND

As a vital osmoticum, proline has an important role in enhancing the tolerance of plants to environmental stress. It is unclear whether the application of exogenous proline can improve the tolerance of Brassica juncea to cadmium (Cd).

RESULTS

This study investigated the effects of different concentrations of proline (20, 40, 60, 80, and 100 mg/L) under Cd stress at different times (0 d, 2 d, and 7 d) on the growth and physiology of B. juncea. Treatment with exogenous proline not only increased the content of proline in B. juncea but also alleviated Cd-induced seedling growth inhibition via the maintenance of higher photosynthetic pigment content and cell viability and a decrease in the content of Cd. Moreover, it increased the activities of antioxidant enzymes and the glutathione/glutathione disulfide ratio to reduce the accumulation of reactive oxygen species. Compared with other concentrations, 60 mg/L of exogenous proline was the most effective at mitigating Cd toxicity in B. juncea.

CONCLUSIONS

Exogenous proline treatment enhanced the tolerance to Cd via a decrease in Cd accumulation and reestablishment of the redox homeostasis in B. juncea.

Differential Response of Phenol Metabolism Associated with Antioxidative Network in Elicited Grapevine Suspension Cultured Cells under Saline Conditions

Highly productive trans-resveratrol (t-R) grapevine suspension cultured cells (SCC) and two effective elicitors, methyl jasmonate (MJ) and randomly methylated β-cyclodextrins (CDs), were used to analyze the extent to which salt treatments alter the production of bioactive phenolic compounds. The expression/activity profile of the enzymes involved in phenol metabolism and antioxidant networks were also studied. A marked extracellular accumulation of phenolic compounds, especially t-R, was found in SCC elicited with CDs and/or MJ under saline conditions. However, the treatments with MJ alone and all those combined with salt favored the intracellular accumulation of catechin and ferulic acid. The salt-induced accumulation of phenolics was correlated with the higher total antioxidant capacity values found in cells, suggesting that cellular redox homeostasis under saline conditions was largely maintained by increasing phenolic compound production. These higher levels of phenolics found in elicited cells under saline conditions fit well with the highest activity of phenylalanine ammonia-lyase. Moreover, antioxidant enzyme activities were boosted in treatments with MJ and/or in those combined with salt and decreased in those treated with CDs. These results suggest a differential response of the antioxidative network to the presence of elicitors under saline conditions.

Transcriptomic Analysis of the Pistacia vera (L.) Fruits Enable the Identification of Genes and Hormone-Related Gene Linked to Inflorescence Bud Abscission

Pistacia vera (L.) is an alternate bearing species. The tree produces axillary inflorescence buds every year. Still, they abscise in “ON” overloaded shoots, causing a limited production in the following “OFF” year, causing a significant and unfavorable production fluctuation. In this work, we carried out de novo discovery and transcriptomic analysis in fruits of “ON” and “OFF” shoots of the cultivar Bianca. We also investigated whether the fruit signaling pathway and hormone biosynthesis directly or indirectly linked to the premature fall of the inflorescence buds causing alternate bearing. We identified 1536 differentially expressed genes (DEGs) in fruits of “ON” vs. “OFF” shoots, which are involved primarily in sugar metabolism, plant hormone pathways and transcription factors. The premature bud abscission linked to the phenomenon is attributable to a lack of nutrients (primarily sugar) and the possible competition between the same branches’ sinks (fruits vs. inflorescence buds). Hormone pathways are involved as a response to signals degradation and remobilization of carbon and nutrients due to the strengthening of the developing embryos. Genes of the secondary metabolism and transcription factors are also involved in tailoring the individual branches response to the nutritional stress and sink competition. Crosstalk among sugar and various hormone-related genes, e.g., ethylene, auxin, ABA and cytokinin, were determined. The discovery of putative biomarkers like callose synthase 5, trehalose-6-phosphate synthase, NAD(P)-linked oxidoreductase and MIOX2, Jasmonate, and salicylic acid-related genes can help to design precision farming practices to mitigate the alternate bearing phenomenon to increase farming profitability. The aim of the analysis is to provide insight into the gene expression profiling of the fate of “ON” and “OFF” fruits associated with the alternate bearing in the pistachio.

A review on adsorptive separation of toxic metals from aquatic system using biochar produced from agro-waste

Water is a basic and significant asset for living beings. Water assets are progressively diminishing due to huge populace development, industrial activities, urbanization and rural exercises. Few heavy metals include zinc, copper, lead, nickel, cadmium and so forth can easily transfer into the water system either direct or indirect activities of electroplating, mining, tannery, painting, fertilizer industries and so forth. The different treatment techniques have been utilized to eliminate the heavy metals from aquatic system, which includes coagulation/flocculation, precipitation, membrane filtration, oxidation, flotation, ion exchange, photo catalysis and adsorption. The adsorption technique is a better option than other techniques because it can eliminate heavy metals even at lower metal ions concentration, simplicity and better regeneration behavior. Agricultural wastes are low-cost biosorbent and typically containing cellulose have the ability to absorb a variety of contaminants. It is important to note that almost all agro wastes are no longer used in their original form but are instead processed in a variety of techniques to improve the adsorption capacity of the substance. The wide range of adsorption capacities for agro waste materials were observed and almost more than 99% removal of toxic pollutants from aquatic systems were achieved using modified agro-waste materials. The present review aims at the water pollution due to heavy metals, as well as various heavy metal removal treatment procedures. The primary objectives of this research is to include an overview of adsorption and various agriculture based adsorbents and its comparison in heavy metal removal.

Crosstalk between the redox signalling and the detoxification: GSTs under redox control?

Reactive oxygen species (ROS), antioxidants and their reduction-oxidation (redox) states all contribute to the redox homeostasis, but glutathione is considered to be the master regulator of it. We aimed to understand the relationship between the redox potential and the diverse glutathione transferase (GST) enzyme family by comparing the stress responses of two tomato cultivars (Solanum lycopersicum 'Moneymaker' and 'Ailsa Craig'). Four-week-old plants were treated by two concentrations of mannitol, NaCl and salicylic acid. The lower H₂O₂ and malondialdehyde contents indicated higher stress tolerance of 'Moneymaker'. The redox status of roots was characterized by measuring the reduced and oxidized form of ascorbate and glutathione spectrophotometrically after 24 h. The redox potential of 'Ailsa Craig' was more oxidized compared to 'Moneymaker' even under control conditions and became more positive due to treatments. High-throughput quantitative real-time PCR revealed that besides overall higher expression levels, SlGSTs were activated more efficiently in 'Moneymaker' due to stresses, resulting in generally higher GST and glutathione peroxidase activities compared to 'Ailsa Craig'. The expression level of SlGSTs correlated differently, however Pearson's correlation analysis showed usually strong positive correlation between SlGST transcription and glutathione redox potential. The possible redox regulation of SlGST expressions was discussed.

Root System Architecture Plasticity of Bread Wheat in Response to Oxidative Burst under Extended Osmotic Stress

There is a demand for an increase in crop production because of the growing population, but water shortage hinders the expansion of wheat cultivation, one of the most important crops worldwide. Polyethylene glycol (PEG) was used to mimic drought stress due to its high osmotic potentials generated in plants subjected to it. This study aimed to determine the root system architecture (RSA) plasticity of eight bread wheat genotypes under osmotic stress in relation to the oxidative status and mitochondrial membrane potential of their root tips. Osmotic stress application resulted in differences in the RSA between the eight genotypes, where genotypes were divided into adapted genotypes that have non-significant decreased values in lateral roots number (LRN) and total root length (TRL), while non-adapted genotypes have a significant decrease in LRN, TRL, root volume (RV), and root surface area (SA). Accumulation of intracellular ROS formation in root tips and elongation zone was observed in the non-adapted genotypes due to PEG-induced oxidative stress. Mitochondrial membrane potential (∆Ψm) was measured for both stress and non-stress treatments in the eight genotypes as a biomarker for programmed cell death as a result of induced osmotic stress, in correlation with RSA traits. PEG treatment increased scavenging capacity of the genotypes from 1.4-fold in the sensitive genotype Gemmiza 7 to 14.3-fold in the adapted genotype Sakha 94. The adapted genotypes showed greater root trait values, ∆Ψm plasticity correlated with high scavenging capacity, and less ROS accumulation in the root tissue, while the non-adapted genotypes showed little scavenging capacity in both treatments, accompanied by mitochondrial membrane permeability, suggesting mitochondrial dysfunction as a result of oxidative stress.

Hormesis in plants: Physiological and biochemical responses

Hormesis is a favorable response to low level exposures to substance or to adverse conditions. This phenomenon has become a target to achieve greater crop productivity. This review aimed to address the physiological mechanisms for the induction of hormesis in plants. Some herbicides present a hormetic dose response. Among them, those with active ingredients glyphosate, 2,4-D and paraquat. The application of glyphosate as a hormesis promoter is therefore showing promess . Glyphosate has prominent role in shikimic acid pathway, decreasing lignin synthesis resulting in improved growth and productivity of several crops. Further studies are still needed to estimate optimal doses for other herbicides of crops or agricultural interest. Biostimulants are also important, since they promote effects on secondary metabolic pathways and production of reactive oxygen species (ROS). When ROS are produced, hydrogen peroxide act as a signaling molecule that promote cell walls malleability allowing inward water transport causing cell expansion. . Plants'ability to overcome several abiotic stress conditions is desirable to avoid losses in crop productivity and economic losses. This review compiles information on how hormesis in plants can be used to achieve new production levels.

The Multiple Roles of Ascorbate in the Abiotic Stress Response of Plants: Antioxidant, Cofactor, and Regulator

Ascorbate (ASC) plays a critical role in plant stress response. The antioxidant role of ASC has been well-studied, but there are still several confusing questions about the function of ASC in plant abiotic stress response. ASC can scavenge reactive oxygen species (ROS) and should be helpful for plant stress tolerance. But in some cases, increasing ASC content impairs plant abiotic stress tolerance, whereas, inhibiting ASC synthesis or regeneration enhances plant stress tolerance. This confusing phenomenon indicates that ASC may have multiple roles in plant abiotic stress response not just as an antioxidant, though many studies more or less ignored other roles of ASC in plant. In fact, ACS also can act as the cofactor of some enzymes, which are involved in the synthesis, metabolism, and modification of a variety of substances, which has important effects on plant stress response. In addition, ASC can monitor and effectively regulate cell redox status. Therefore, we believe that ASC has atleast triple roles in plant abiotic stress response: as the antioxidant to scavenge accumulated ROS, as the cofactor to involve in plant metabolism, or as the regulator to coordinate the actions of various signal pathways under abiotic stress. The role of ASC in plant abiotic stress response is important and complex. The detail role of ASC in plant abiotic stress response should be analyzed according to specific physiological process in specific organ. In this review, we discuss the versatile roles of ASC in the response of plants to abiotic stresses.

Molecular mechanisms of plant adaptive responses to heavy metals stress

Heavy metals (HMs) are among the main environmental pollutants that can enter the soil, water bodies, and the atmosphere as a result of natural processes (weathering of rocks, volcanic activity), and also as a result of human activities (mining, metallurgical and chemical industries, transport, application of mineral fertilizers). Plants counteract the HMs stresses through morphological and physiological adaptations, which are imparted through well-coordinated molecular mechanisms. New approaches, which include transcriptomics, genomics, proteomics, and metabolomics analyses, have opened the paths to understand such complex networks. This review sheds light on molecular mechanisms included in plant adaptive and defense responses during metal stress. It is focused on the entry of HMs into plants, its transport and accumulation, effects on the main physiological processes, gene expressions included in plant adaptive and defense responses during HM stress. Analysis of new data allowed the authors to conclude that the most important mechanism of HM tolerance is extracellular and intracellular HM sequestration. Organic anions (malate, oxalate, etc.) provide extracellular sequestration of HM ions. Intracellular HM sequestration depends not only on a direct binding mechanism with different polymers (pectin, lignin, cellulose, hemicellulose, etc.) or organic anions but also on the action of cellular receptors and transmembrane transporters. We focused on the functioning chloroplasts, mitochondria, and the Golgi complex under HM stress. The currently known molecular mechanisms of plant tolerance to the toxic effects of HMs are analyzed.

Glutathione Enhances Auxin Sensitivity in Arabidopsis Roots

Root development is regulated by the tripeptide glutathione (GSH), a strong non-enzymatic antioxidant found in plants but with a poorly understood function in roots. Here, Arabidopsis mutants deficient in GSH biosynthesis (cad2, rax1, and rml1) and plants treated with the GSH biosynthesis inhibitor buthionine sulfoximine (BSO) showed root growth inhibition, significant alterations in the root apical meristem (RAM) structure (length and cell division), and defects in lateral root formation. Investigation of the molecular mechanisms of GSH action showed that GSH deficiency modulated total ubiquitination of proteins and inhibited the auxin-related, ubiquitination-dependent degradation of Aux/IAA proteins and the transcriptional activation of early auxin-responsive genes. However, the DR5 auxin transcriptional response differed in root apical meristem (RAM) and pericycle cells. The RAM DR5 signal was increased due to the up-regulation of the auxin biosynthesis TAA1 protein and down-regulation of PIN4 and PIN2, which can act as auxin sinks in the root tip. The transcription auxin response (the DR5 signal and expression of auxin responsive genes) in isolated roots, induced by a low (0.1 µM) auxin concentration, was blocked following GSH depletion of the roots by BSO treatment. A higher auxin concentration (0.5 µM) offset this GSH deficiency effect on DR5 expression, indicating that GSH deficiency does not completely block the transcriptional auxin response, but decreases its sensitivity. The ROS regulation of GSH, the active GSH role in cell proliferation, and GSH cross-talk with auxin assume a potential role for GSH in the modulation of root architecture under stress conditions.

The Chloroplast Reactive Oxygen Species-Redox System in Plant Immunity and Disease

Pathogen infections limit plant growth and productivity, thus contributing to crop losses. As the site of photosynthesis, the chloroplast is vital for plant productivity. This organelle, communicating with other cellular compartments challenged by infection (e.g., apoplast, mitochondria, and peroxisomes), is also a key battlefield in the plant-pathogen interaction. Here, we focus on the relation between reactive oxygen species (ROS)-redox signaling, photosynthesis which is governed by redox control, and biotic stress response. We also discuss the pathogen strategies to weaken the chloroplast-mediated defense responses and to promote pathogenesis. As in the next decades crop yield increase may depend on the improvement of photosynthetic efficiency, a comprehensive understanding of the integration between photosynthesis and plant immunity is required to meet the future food demand.

Ascorbate glutathione-dependent H2O2 scavenging is an important process in axillary bud outgrowth in rosebush

BACKGROUND AND AIMS

Branching is an important mechanism of plant shape establishment and the direct consequence of axillary bud outgrowth. Recently, hydrogen peroxide (H2O2) metabolism, known to be involved in plant growth and development, has been proposed to contribute to axillary bud outgrowth. However, the involvement of H2O2 in this process remains unclear.

METHODS

We analysed the content of H2O2 during bud outgrowth and characterized its catabolism, both at the transcriptional level and in terms of its enzymatic activities, using RT-qPCR and spectrophotometric methods, respectively. In addition, we used in vitro culture to characterize the effects of H2O2 application and the reduced glutathione (GSH) synthesis inhibitor l-buthionine sulfoximine (BSO) on bud outgrowth in relation to known molecular markers involved in this process.

KEY RESULTS

Quiescent buds displayed a high content of H2O2 that declined when bud outgrowth was initiated, as the consequence of an increase in the scavenging activity that is associated with glutathione pathways (ascorbate-glutathione cycle and glutathione biosynthesis); catalase did not appear to be implicated. Modification of bud redox state after the application of H2O2 or BSO prevented axillary bud outgrowth by repressing organogenesis and newly formed axis elongation. Hydrogen peroxide also repressed bud outgrowth-associated marker gene expression.

CONCLUSIONS

These results show that high levels of H2O2 in buds that are in a quiescent state prevents bud outgrowth. Induction of ascorbate-glutathione pathway scavenging activities results in a strong decrease in H2O2 content in buds, which finally allows bud outgrowth.

Local and Systemic Changes in Photosynthetic Parameters and Antioxidant Activity in Cucumber Challenged with Pseudomonas syringae pv lachrymans

We studied changes in gas exchange, photochemical activity and the antioxidant system in cucumber leaves locally infected with Pseudomonas syringae pv lachrymans and in uninfected systemic ones. Infection-induced declined net photosynthesis rate and the related changes in transpiration rate, the intracellular CO2 concentration, and prolonged reduction in maximal PSII quantum yield (Fv/Fm), accompanied by an increase in non-photochemical quenching (NPQ), were observed only in the infected leaves, along with full disease symptom development. Infection severely affected the ROS/redox homeostasis at the cellular level and in chloroplasts. Superoxide dismutase, ascorbate, and tocopherol were preferentially induced at the early stage of pathogenesis, whereas catalase, glutathione, and the ascorbate-glutathione cycle enzymes were activated later. Systemic leaves retained their net photosynthesis rate and the changes in the antioxidant system were partly like those in the infected leaves, although they occurred later and were less intense. Re-balancing of ascorbate and glutathione in systemic leaves generated a specific redox signature in chloroplasts. We suggest that it could be a regulatory element playing a role in integrating photosynthesis and redox regulation of stress, aimed at increasing the defense capacity and maintaining the growth of the infected plant.

Melatonin Suppressed the Heat Stress-Induced Damage in Wheat Seedlings by Modulating the Antioxidant Machinery

Melatonin (N-acetyl-5-methoxytryptamine) is a pleiotropic signaling molecule that plays a crucial role in the regulation of various environmental stresses, including heat stress (HS). In this study, a 100 μM melatonin (MT) pretreatment followed by exposure to heat stress for different time periods was found to efficiently reduce oxidative stress by preventing the over-accumulation of hydrogen peroxide (H₂O₂), lowering the lipid peroxidation content (malondialdehyde (MDA) content), and increasing proline (Pro) biosynthesis. Moreover, the activities of antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), were increased substantially in MT-pretreated wheat seedlings. The presence of MT significantly improved the heat tolerance of wheat seedlings by modulating their antioxidant defense system, activating the ascorbate–glutathione (AsA–GSH) cycle comprising ascorbate peroxidase (APX), and increasing glutathione reductase (GR) activities. It also held the photosynthetic machinery stable by increasing the chlorophyll content. Enhancement in the endogenous MT contents was also observed in the MT+HS-treated plants. Furthermore, the expression of reactive oxygen species (ROS)-related genes TaSOD, TaPOD, and TaCAT, and anti-stress responsive genes, such as TaMYB80, TaWRKY26, and TaWRKY39, was also induced in MT-treated seedlings. Due to these notable changes, an improvement in stress resistance was observed in MT-treated seedlings compared with control. Taken together, our findings suggest that MT can play a key role in boosting the stress tolerance of plants by modulating the antioxidant defense system and regulating the transcription of stress-responsive genes.

Fertilizer Rate-Associated Increase in Foliar Jasmonate Burst Observed in Wounded Arabidopsis thaliana Leaves is Attenuated at eCO2

The predicted future increase in tropospheric carbon dioxide (CO2) levels will have major effects on C3 plants and their interactions with other organisms in the biosphere. In response to attack by chewing arthropod herbivores or nectrotrophic pathogens, many plants mount a rapid and intense increase in jasmonate-related phytohormones that results in a robust defense response; however, previous studies have shown that C3 plants grown at elevated CO2 may have lower induced jasmonate levels, particularly in well nitrate-fertilized plants. Given the relationship between atmospheric CO2, photorespiration, cellular reductant and redox status, nitrogen assimilation and phytohormones, we compared wound-induced responses of the C3 plant Arabidopsis thaliana. These plants were fertilized at two different rates (1 or 10 mM) with nitrate or ammonium and grown at ambient or elevated CO2. In response to artificial wounding, an increase in cellular oxidative status leads to a strong increase in jasmonate phytohormones. At ambient CO2, increased oxidative state of nitrate-fertilized plants leads to a robust 7-iso-jasmonyl-L-isoleucine increase; however, the strong fertilizer rate-associated increase is alleviated in plants grown at elevated CO2. As well, the changes in ascorbate in response to wounding and wound-induced salicylic acid levels may also contribute to the suppression of the jasmonate burst. Understanding the mechanism underlying the attenuation of the jasmonate burst at elevated CO2 has important implications for fertilization strategies under future predicted climatic conditions.

Hydrogen Peroxide Production by the Spot-Like Mode Action of Bisphenol A

Bisphenol A (BPA), an intermediate chemical used for synthesizing polycarbonate plastics, has now become a wide spread organic pollutant. It percolates from a variety of sources, and plants are among the first organisms to encounter, absorb, and metabolize it, while its toxic effects are not yet fully known. Therefore, we experimentally studied the effects of aqueous BPA solutions (50 and 100 mg L^-1, for 6, 12, and 24 h) on photosystem II (PSII) functionality and evaluated the role of reactive oxygen species (ROS) on detached leaves of the model plant Arabidopsis thaliana. Chlorophyll fluorescence imaging analysis revealed a spatiotemporal heterogeneity in the quantum yields of light energy partitioning at PSII in Arabidopsis leaves exposed to BPA. Under low light PSII function was negatively influenced only at the spot-affected BPA zone in a dose- and time-dependent manner, while at the whole leaf only the maximum photochemical efficiency (Fv/Fm) was negatively affected. However, under high light all PSII photosynthetic parameters measured were negatively affected by BPA application, in a time-dependent manner. The affected leaf areas by the spot-like mode of BPA action showed reduced chlorophyll autofluorescence and increased accumulation of hydrogen peroxide (H₂O₂). When H₂O₂ was scavenged via N-acetylcysteine under BPA exposure, PSII functionality was suspended, while H₂O₂ scavenging under non-stress had more detrimental effects on PSII function than BPA alone. It can be concluded that the necrotic death-like spots under BPA exposure could be due to ROS accumulation, but also H₂O₂ generation seems to play a role in the leaf response against BPA-related stress conditions.

Comparative analyses of glutathione system of vacuoles and leucoplasts isolated from the storage parenchyma cells of dormant red beetroots (Beta vulgaris L.)

The role of glutathione in the plant vacuole is still being debated. In the present paper, the redox state of glutathione and the activity of glutathione S-transferase (GST, E 2.5.1.18) in the vacuole compared to those in leucoplast have been studied. Organelles were isolated from dormant red beet (Beta vulgaris L.) taproots. Two generally used approaches have been applied to quantitatively assess the content of glutathione. Initially, levels of glutathione were measured in isolated organelles after labeling with monochlorobimane (MCB) and imaging with the use of confocal laser scanning microscopy. However, there are factors limiting the specificity of this method, because of which the resulting concentrations of vacuolar GSH have been underestimated. Another approach used was HPLC, which allows to simultaneously quantify the reduced glutathione (GSH) and glutathione disulfide (GSSG). The concentration of the total glutathione (GSHt) and GSSG in vacuoles determined with the aid of HPLC-UV was higher in comparison to that in the leucoplasts. The reduction potential (E_h) for the glutathione couple in the vacuoles was more positive (-163 mV), than that in plastids (-282 mV). The relatively rapid increase in fluorescence in the isolated vacuoles and plastids during MCB-labeling has indicated to the contribution of GSTs, since the conjugation of GSH to bimane is catalysed by these enzymes. The GST activity in the vacuoles has been assessed to be quite high compared to that of leucoplasts. The number of isoforms of GSTs also differed markedly in vacuoles and plastids. Collectively, our findings suggest the idea that the glutathione accumulated by central vacuole seems to contribute to the redox processes and to the detoxification, which can take place in this compartment.

Glutathione Can Compensate for Salicylic Acid Deficiency in Tobacco to Maintain Resistance to Tobacco Mosaic Virus

Earlier studies showed that the artificial elevation of endogenous glutathione (GSH) contents can markedly increase the resistance of plants against different viruses. On the other hand, salicylic acid (SA)-deficient NahG plants display enhanced susceptibility to viral infections. In the present study, the biochemical mechanisms underlying GSH-induced resistance were investigated in various tobacco biotypes displaying markedly different GSH and SA levels. The endogenous GSH levels of Nicotiana tabacum cv. Xanthi NN and N. tabacum cv. Xanthi NN NahG tobacco leaves were increased by infiltration of exogenous GSH or its synthetic precursor R-2-oxo-4-thiazolidine-carboxylic acid (OTC). Alternatively, we also used tobacco lines containing high GSH levels due to transgenes encoding critical enzymes for cysteine and GSH biosynthesis. We crossed Xanthi NN and NahG tobaccos with the GSH overproducer transgenic tobacco lines in order to obtain F1 progenies with increased levels of GSH and decreased levels of SA. We demonstrated that in SA-deficient NahG tobacco the elevation of in planta GSH and GSSG levels either by exogenous GSH or by crossing with glutathione overproducing plants confers enhanced resistance to Tobacco mosaic virus (TMV) manifested as both reduced symptoms (i.e. suppression of hypersensitive-type localized necrosis) and lower virus titers. The beneficial effects of elevated GSH on TMV resistance was markedly stronger in NahG than in Xanthi NN leaves. Infiltration of exogenous GSH and OTC or crossing with GSH overproducer tobacco lines resulted in a substantial rise of bound SA and to a lesser extent of free SA levels in tobacco, especially following TMV infection. Significant increases in expression of pathogenesis related (NtPR-1a, and NtPRB-1b), and glutathione S-transferase (NtGSTtau, and NtGSTphi) genes were evident in TMV-inoculated leaves in later stages of pathogenesis. However, the highest levels of defense gene expression were associated with SA-deficiency, rather than enhanced TMV resistance. In summary, elevated levels of glutathione in TMV-infected tobacco can compensate for SA deficiency to maintain virus resistance. Our results suggest that glutathione-induced redox changes are important components of antiviral signaling in tobacco.

A perspective on ecologically relevant plant-UV research and its practical application

Plants perceive ultraviolet-B (UV-B) radiation through the UV-B photoreceptor UV RESISTANCE LOCUS 8 (UVR8), and initiate regulatory responses via associated signalling networks, gene expression and metabolic pathways. Various regulatory adaptations to UV-B radiation enable plants to harvest information about fluctuations in UV-B irradiance and spectral composition in natural environments, and to defend themselves against UV-B exposure. Given that UVR8 is present across plant organs and tissues, knowledge of the systemic signalling involved in its activation and function throughout the plant is important for understanding the context of specific responses. Fine-scale understanding of both UV-B irradiance and perception within tissues and cells requires improved application of knowledge about UV-attenuation in leaves and canopies, warranting greater consideration when designing experiments. In this context, reciprocal crosstalk among photoreceptor-induced pathways also needs to be considered, as this appears to produce particularly complex patterns of physiological and morphological response. Through crosstalk, plant responses to UV-B radiation go beyond simply UV-protection or amelioration of damage, but may give cross-protection over a suite of environmental stressors. Overall, there is emerging knowledge showing how information captured by UVR8 is used to regulate molecular and physiological processes, although understanding of upscaling to higher levels of organisation, i.e. organisms, canopies and communities remains poor. Achieving this will require further studies using model plant species beyond Arabidopsis, and that represent a broad range of functional types. More attention should also be given to plants in natural environments in all their complexity, as such studies are needed to acquire an improved understanding of the impact of climate change in the context of plant-UV responses. Furthermore, broadening the scope of experiments into the regulation of plant-UV responses will facilitate the application of UV radiation in commercial plant production. By considering the progress made in plant-UV research, this perspective highlights prescient topics in plant-UV photobiology where future research efforts can profitably be focussed. This perspective also emphasises burgeoning interdisciplinary links that will assist in understanding of UV-B effects across organisational scales and gaps in knowledge that need to be filled so as to achieve an integrated vision of plant responses to UV-radiation.

The Arabidopsis glutathione transferases, AtGSTF8 and AtGSTU19 are involved in the maintenance of root redox homeostasis affecting meristem size and salt stress sensitivity

The tau (U) and phi (F) classes of glutathione transferase (GST) enzymes reduce the glutathione (GSH) pool using GSH as a co-substrate, thus influence numerous redox-dependent processes including hormonal and stress responses. We performed detailed analysis of the redox potential and reactive oxygen species levels in longitudinal zones of 7-day-old roots of Arabidopsis thaliana L. Col-0 wild type and Atsgtf8 and Atgstu19 insertional mutants. Using redox-sensitive cytosolic green fluorescent protein (roGFP2) the redox status of the meristematic, transition, and elongation zones was determined under control and salt stress (3-hour of 75 or 150 mM NaCl treatment) conditions. The Atgstu19 mutant had the most oxidized redox status in all root zones throughout the experiments. Using fluorescent dyes significantly higher superoxide radical (O₂^-) levels was detected in both Atgst mutants than in the Col-0 control. Salt treatment resulted in the highest O₂^- increase in the Atgstf8 root, while the amount of H₂O₂ elevated most in the case of Atgstu19. Moreover, vitality decreased in Atgstu19 roots more than in wild type under salt stress. Our results indicate that AtGSTF8 and especially the AtGSTU19 proteins function in the root fine-tuning the redox homeostasis both under control and salt stress conditions.

The chaperone-like protein CDC48 regulates ascorbate peroxidase in tobacco

There is increasing evidence that the chaperone-like protein CDC48 (cell division cycle 48) plays a role in plant immunity. Cytosolic ascorbate peroxidase (cAPX), which is a major regulator of the redox status of plant cells, has previously been shown to interact with CDC48. In this study, we examined the regulation of cAPX by the ATPase NtCDC48 during the cryptogein-induced immune response in tobacco cells. Our results not only confirmed the interaction between the proteins but also showed that it occurs in the cytosol. cAPX accumulation was modified in cells overexpressing NtCDC48, a process that was shown to involve post-translational modification of cAPX. In addition, cryptogein-induced increases in cAPX activity were suppressed in cells overexpressing NtCDC48 and the abundance of the cAPX dimer was below the level of detection. Furthermore, the levels of both reduced (GSH) and oxidized glutathione (GSSG) and the GSH/GSSG ratio decreased more rapidly in response to the elicitor in these cells than in controls. A decrease in cAPX activity was also observed in response to heat shock in the cells overexpressing NtCDC48, indicating that the regulation of cAPX by NtCDC48 is not specific to the immune response.

Functional Mechanisms Underlying the Antimicrobial Activity of the Oryza sativa Trx-like Protein

Plants are constantly subjected to a variety of environmental stresses and have evolved regulatory responses to overcome unfavorable conditions that might reduce or adversely change a plant’s growth or development. Among these, the regulated production of reactive oxygen species (ROS) as a signaling molecule occurs during plant development and pathogen defense. This study demonstrates the possible antifungal activity of Oryza sativa Tetratricopeptide Domain-containing thioredoxin (OsTDX) protein against various fungal pathogens. The transcription of OsTDX was induced by various environmental stresses known to elicit the generation of ROS in plant cells. OsTDX protein showed potent antifungal activity, with minimum inhibitory concentrations (MICs) against yeast and filamentous fungi ranging between 1.56 and 6.25 and 50 and 100 µg/mL, respectively. The uptake of SYTOX-Green into fungal cells and efflux of calcein from artificial fungus-like liposomes suggest that its killing mechanism involves membrane permeabilization and damage. In addition, irregular blebs and holes apparent on the surfaces of OsTDX-treated fungal cells indicate the membranolytic action of this protein. Our results suggest that the OsTDX protein represents a potentially useful lead for the development of pathogen-resistant plants.

Redox and thylakoid membrane proteomic analysis reveals the Momordica (Momordica charantia L.) rootstock-induced photoprotection of cucumber leaves under short-term heat stress

Heat stress adversely affects plant physiological and metabolic processes and is considered an important constraint on crop growth and productivity in agriculture worldwide. Grafting techniques are capable of mitigating various stresses. Here, compared with self-grafted cucumbers subjected to 42 °C heat stress for 24 h, we found that Momordica-grafted cucumbers exhibited higher cytomembrane thermostability, less photoinhibition reflected by their chlorophyll fluorescence, and a reduction in oxidative stress. To better understand the mechanism, optimized Blue-Native/SDS-PAGE two-dimensional electrophoresis (2-DE) was firstly applied to entire thylakoid membrane of grafted cucumbers, and 25 significantly differential accumulated protein spots were identified by MALDI-TOF/TOF MS analysis. The proteomic analysis revealed that high temperatures suppressed the accumulation of 13 proteins in self-grafted cucumbers, while Momordica rootstock stimulated the accumulation of 12 of these proteins. The transcriptional analysis indicated that grafting onto Momordica significantly increased the expression of genes that encode the photosystem II subunit S (PsbS) and minor light-harvesting complexes (CP24, CP26 and CP29.1), which are closely associated with non-photochemical quenching (NPQ) after heat shock. Immunoblotting for PsbS corroborated the Momordica-induced acceleration of heat dissipation. Taken together, Momordica rootstock alleviated heat-induced photoinhibition by maintaining intracellular redox homeostasis, stabilizing the protein library of the thylakoid membrane and modulating NPQ in the scions.

Time-course analysis of salicylic acid effects on ROS regulation and antioxidant defense in roots of hulled and hulless barley under combined stress of drought, heat and salinity

Greater crop losses can result from simultaneous exposure to a combination of drought, heat and salinity in the field. Salicylic acid (SA), a phenolic phytohormone, can affect a range of physiological and biochemical processes in plants and significantly impacts their resistance to these abiotic stresses. Despite numerous reports involving the positive effects of SA by applying each abiotic stress separately, the mechanism of SA-mediated adaptation to combined stresses remains elusive. This study, via a time-course analysis, investigated the role of SA on the roots of hulled and hulless (naked) barley (Hordeum vulgare L. 'Tarm' and 'Özen', respectively), which differed in salt tolerance, under the combined stress of drought, heat and salt. The combined stress caused marked reductions in root length and increases in proline content in both genotypes; however, Tarm exhibited better adaptation to the triple stress. Under the first 24 h of stress, superoxide dismutase (SOD; EC.1.15.1.1) and peroxidase (POX; EC.1.11.1.7) activity in the Tarm roots increased remarkably, while decreasing in the Özen roots. Furthermore, the Tarm roots showed higher catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APX; EC 1.11.1.11) and glutathione reductase (GR; EC 1.6.4.2) activity than the Özen during the combined stresses. The sensitivity of hulless barley roots may be related to decreasing SOD, POX, CAT and GR activity under stress. Over 72 h of stress, the SA pretreatment improved the APX and GR activity in Tarm and that of POX and CAT in Özen, demonstrating that exogenously applied SA regulates antioxidant defense enzymes in order to detoxify reactive oxygen species. The results of this study suggest that SA treatment may improve the triple-stress combination tolerance in hulled and hulless barley cultivars by increasing the level of antioxidant enzyme activity and promoting the accumulation of proline. Thus, SA alleviated the damaging effects of the triple stress by improving the antioxidant system, although these effects differed depending on characteristic of the hull of the grain.

Plant Glutathione Transferases and Light

The activity and expression of glutathione transferases (GSTs) depend on several less-known endogenous and well-described exogenous factors, such as the developmental stage, presence, and intensity of different stressors, as well as on the absence or presence and quality of light, which to date have received less attention. In this review, we focus on discussing the role of circadian rhythm, light quality, and intensity in the regulation of plant GSTs. Recent studies demonstrate that diurnal regulation can be recognized in GST activity and gene expression in several plant species. In addition, the content of one of their co-substrates, reduced glutathione (GSH), also shows diurnal changes. Darkness, low light or shade mostly reduces GST activity, while high or excess light significantly elevates both the activity and expression of GSTs and GSH levels. Besides the light-regulated induction and dark inactivation of GSTs, these enzymes can also participate in the signal transduction of visible and UV light. For example, red light may alleviate the harmful effects of pathogens and abiotic stressors by increasing GST activity and expression, as well as GSH content in leaves of different plant species. Based on this knowledge, further research on plants (crops and weeds) or organs and temporal regulation of GST activity and gene expression is necessary for understanding the complex regulation of plant GSTs under various light conditions in order to increase the yield and stress tolerance of plants in the changing environment.

Plant-lead interactions: Transport, toxicity, tolerance, and detoxification mechanisms

Natural and human activities introduced an excess level of toxic lead (Pb) to the environment. Pb has no known biological significance and its interactions with plants lead to the production of reactive oxygen species (ROS). Pb and/or ROS have the potential to cause phytotoxicity by damaging the tissue ultrastructure, cellular components, and biomolecules. These damaging effects may possibly result in the inhibition of normal cellular functioning, physiological reactions, and overall plant performances. ROS play a dual role and act as a signaling molecule in plant defense system. This system encircles enzymatic and non-enzymatic antioxidative mechanisms. Catalase, superoxide dismutase, peroxidase, and enzymes from the ascorbate-glutathione cycle are the major enzymatic antioxidants, while non-enzymatic antioxidants include phenols, flavonoids, ascorbic acid, and glutathione. Pb removal from contaminated sites using plants depend on the plant's Pb accumulation capacity, Pb-induced phytotoxicity, and tolerance and detoxification mechanisms plants adopted to combat against this phytotoxicity. However, the consolidated information discussing Pb-plant interaction including Pb uptake and its translocation within tissues, Pb-mediated phytotoxic symptoms, antioxidative mechanisms, cellular, and protein metabolisms are rather limited. Thus, we aimed to present a consolidated information and critical discussions focusing on the recent studies related to the Pb-induced toxicity and oxidative stress situations in different plants. The important functions of different antioxidants in plants during Pb stress have been reviewed. Additionally, tolerance responses and detoxification mechanisms in the plant through the regulation of gene expression, and glutathione and protein metabolisms to compete against Pb-induced phytotoxicity are also briefly discussed herein.

Suppression of External NADPH Dehydrogenase-NDB1 in Arabidopsis thaliana Confers Improved Tolerance to Ammonium Toxicity via Efficient Glutathione/Redox Metabolism

Environmental stresses, including ammonium (NH₄⁺) nourishment, can damage key mitochondrial components through the production of surplus reactive oxygen species (ROS) in the mitochondrial electron transport chain. However, alternative electron pathways are significant for efficient reductant dissipation in mitochondria during ammonium nutrition. The aim of this study was to define the role of external NADPH-dehydrogenase (NDB1) during oxidative metabolism of NH₄⁺-fed plants. Most plant species grown with NH₄⁺ as the sole nitrogen source experience a condition known as “ammonium toxicity syndrome”. Surprisingly, transgenic Arabidopsis thaliana plants suppressing NDB1 were more resistant to NH₄⁺ treatment. The NDB1 knock-down line was characterized by milder oxidative stress symptoms in plant tissues when supplied with NH₄⁺. Mitochondrial ROS accumulation, in particular, was attenuated in the NDB1 knock-down plants during NH₄⁺ treatment. Enhanced antioxidant defense, primarily concerning the glutathione pool, may prevent ROS accumulation in NH₄⁺-grown NDB1-suppressing plants. We found that induction of glutathione peroxidase-like enzymes and peroxiredoxins in the NDB1-surpressing line contributed to lower ammonium-toxicity stress. The major conclusion of this study was that NDB1 suppression in plants confers tolerance to changes in redox homeostasis that occur in response to prolonged ammonium nutrition, causing cross tolerance among plants.

Coordinated role of soluble and cell wall bound phenols is a key feature of the metabolic adjustment in a mining woody fleabane (Dittrichia viscosa L.) population under semi-arid conditions

Environmental contamination by hazardous heavy metals/metalloids (metal(loid)s) is growing worldwide. To restrict the migration of toxic contaminants, the establishment of a self-sustainable plant cover is required. Plant growth in multi-polluted soils is a challenging issue not only by metal(loid) toxicities, but also by the co-occurrence of other stressors. Dittrichia viscosa is a pioneer Mediterranean species able to thrive in metal(loid)-enriched tailings in semi-arid areas. The aim of the present work was to examine the metabolic adjustments involved in the acclimation responses of this plant to conditions prevailing in mine-tailings during Mediterranean spring and summer. For this purpose, fully-expanded leaves, and rhizosphere soil of both mining and non-mining populations of D. viscosa grown spontaneously in south-eastern Spain were sampled in two consecutive years. Quantitative analysis of >50 biochemical, physiological and edaphic parameters were performed, including nutrient status, metal(loid) contents, leaf redox components, primary and secondary metabolites, salicylic acid levels, and soil physicochemical properties. Results showed that mining plants exhibited high foliar Zn/Pb co-accumulation capacity, without substantially affecting their photosynthetic metabolism or nutritional status even in the driest summer period. The comparison of the antioxidative/oxidative profile between mining and non-mining D. viscosa populations revealed no major seasonal changes in the content of primary antioxidants (ascorbate and GSH), or in the levels of ROS. Multivariate analysis showed that phenylalanine ammonia-lyase (PAL) and peroxidase (PRX) activities and soluble and cell wall-bound phenols were potential biomarkers for discriminating between both populations. During the dry season, a marked enhancement in the activity of both PAL and soluble PRX resulted in both a drop in the accumulation of soluble phenols and an increase of the strong metal chelator caffeic acid in the cell-wall fraction, supporting the view that the plasticity of phenylpropanoid metabolism provide an effective way to counteract the effects of stress combinations.

Transcriptomic and proteomic feature of salt stress-regulated network in Jerusalem artichoke (Helianthus tuberosus L.) root based on de novo assembly sequencing analysis

Ribosome activation and sugar metabolic process mainly act on the regulation of salt tolerance in the bioenergy crop Helianthus tuberosus L. as dissected by integrated transcriptomic and proteomic analyses. Helianthus tuberosus L. is an important halophyte plant that can survive in saline-alkali soil. It is vitally necessary to build an available genomic resource to investigate the molecular mechanisms underlying salt tolerance in H. tuberosus. De novo assembly and annotation of transcriptomes were built for H. tuberosus using a HiSeq 4000 platform. 293,823 transcripts were identified and annotated into 190,567 unigenes. In addition, iTRAQ-labeled quantitative proteomics was carried out to detect global protein profiling as a response to salt stress. Comparative omics analysis showed that 5432 genes and 43 proteins were differentially expressed in H. tuberosus under salt stress, which were enriched in the following processes: carbohydrate metabolism, ribosome activation and translation, oxidation-reduction and ion binding. The reprogramming of transcript and protein works suggested that the induced activity of ribosome and sugar signaling may endue H. tuberosus with salt tolerance. With high-quality sequencing and annotation, the obtained transcriptomics and proteomics provide a robust genomic resource for dissecting the regulatory molecular mechanism of H. tuberosus in response to salt stress.

Changes in redox regulation during transition from C3 to single cell C4 photosynthesis in Bienertia sinuspersici

Bienertia sinuspersici performs single cell C₄ photosynthesis without Kranz anatomy. Peripheral and central cytoplasmic compartments in a single chlorenchyma cell act as mesophyll cells and bundle sheath cells. Development of this specialized mechanism is gradual during plant development. Young leaves perform C₃ photosynthesis, while mature leaves have complete C₄ cycle. The aim of this work was to investigate changes in redox regulation and antioxidant defence during transition from C₃ to single cell C₄ photosynthesis in B. sinuspersici leaves. First, we confirmed gradual development of C₄ with protein blot and qRT-PCR analysis of C₄ enzymes. After this activities and isoenzymes of superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX), glutathione reductase (GR), dehydroascorbate reductase (DHAR) and H₂O₂ and TBARS and glutathione pool and redox status (GSH/GSSG) were determined in young, developing and mature leaves during transition from C₃ to single cell C₄ photosynthesis. Activities of SOD, APX and POX decrease, while GR and DHAR were increased. However, most striking results were the changes in isoenzyme patterns of SOD, CAT and GR which were gradual through transition to C₄ photosynthesis.

Allium cepa L. Response to Sodium Selenite (Se(IV)) Studied in Plant Roots by a LC-MS-Based Proteomic Approach

Liquid chromatography-high-resolution mass spectrometry was used for the first time to investigate the impact of Se(IV) (10 mgSe L^-1 as sodium selenite) on Allium cepa L. root proteome. Using MaxQuant platform, more than 600 proteins were found; 42 were identified based on at least 2 razor + unique peptides, score > 25, and were found to be differentially expressed in the exposed versus control roots with t-test difference > ±0.70 (p < 0.05, Perseus). Se(IV) caused growth inhibition and the decrease of total RNA in roots. Different abundances of proteins involved in transcriptional regulation, protein folding/assembly, cell cycle, energy/carbohydrate metabolism, stress response, and antioxidant defense were found in the exposed vs nonexposed roots. New evidence was obtained on the alteration of sulfur metabolism due to S-Se competition in A. cepa L. which, together with the original analytical approach, is the main scientific contribution of this study. Specifically, proteins participating in assimilation and transformation of both elements were affected; formation of volatile Se compounds seemed to be favored. Changes observed in methionine cycle suggested that Se(IV) stress might repress methylation capability in A. cepa L., potentially limiting accumulation of Se in the form of nonprotein methylated species and affecting adversely transmethylation-dependent signaling pathways.

Ascorbic acid deficiency leads to increased grain chalkiness in transgenic rice for suppressed of L-GalLDH

The grain chalkiness of rice (Oryza sativa L.), which determines the rice quality and price, is a major concern in rice breeding. Reactive oxygen species (ROS) plays a critical role in regulating rice endosperm chalkiness. Ascorbic acid (Asc) is a major plant antioxidant, which strictly regulates the levels of ROS. l-galactono-1, 4-lactone dehydrogenase (L-GalLDH, EC 1.3.2.3) is an enzyme that catalyzes the last step of Asc biosynthesis in higher plants. Here we show that the L-GalLDH-suppressed transgenic rice, GI-1 and GI-2, which have constitutively low (between 30% and 50%) leaf and grain Asc content compared with the wild-type (WT), exhibit significantly increased grain chalkiness. Further examination showed that the deficiency of Asc resulted in a higher lipid peroxidation and H₂O₂ content, accompanied by a lower hydroxyl radical scavenging rate, total antioxidant capacity and photosynthetic ability. In addition, changes of the enzyme activities and gene transcript abundances related to starch synthesis were also observed in GI-1 and GI-2 grains. The results we presented here suggest a close correlation between Asc deficiency and grain chalkiness in the L-GalLDH-suppressed transgenics. Asc deficiency leads to the accumulation of H₂O₂, affecting antioxidant capacity and photosynthetic function, changing enzyme activities and gene transcript abundances related to starch synthesis, finally leading to the increased grain chalkiness.

Seasonal changes in antioxidative/oxidative profile of mining and non-mining populations of Syrian beancaper as determined by soil conditions

Soil pollution by heavy metals/metalloids (HMMs) is a problem worldwide. To prevent dispersion of contaminated particles by erosion, the maintenance of a vegetative cover is needed. Successful plant establishment in multi-polluted soils can be hampered not only by HMM toxicities, but also by soil nutrient deficiencies and the co-occurrence of abiotic stresses. Some plant species are able to thrive under these multi-stress scenarios often linked to marked fluctuations in environmental factors. This study aimed to investigate the metabolic adjustments involved in Zygophyllum fabago acclimative responses to conditions prevailing in HMM-enriched mine-tailings piles, during Mediterranean spring and summer. To this end, fully expanded leaves, and rhizosphere soil, of three contrasting mining and non-mining populations of Z. fabago grown spontaneously in south-eastern Spain were sampled in two consecutive years. Approximately 50 biochemical, physiological and edaphic parameters were examined, including leaf redox components, primary and secondary metabolites, endogenous levels of salicylic acid, and physicochemical properties of soil (fertility parameters and total concentration of HMMs). Multivariate data analysis showed a clear distinction in antioxidative/oxidative profiles between and within the populations studied. Levels of chlorophylls, proteins and proline characterized control plants whereas antioxidant capacity and C- and S-based antioxidant compounds were biomarkers of mining plants. Seasonal variations were characterized by higher levels of alkaloids and PAL and soluble peroxidase activities in summer, and by soluble sugars and hydroxycinnamic acids in spring irrespective of the population considered. Although the antioxidant systems are subjected to seasonal variations, the way and the intensity with which every population changes its antioxidative/oxidative profile seem to be determined by soil conditions. In short, Z. fabago displays a high physiological plasticity that allow it to successfully shift its metabolism to withstand the multiple stresses that plants must cope with in mine tailings piles under Mediterranean climatic conditions.

Comparative photochemistry activity and antioxidant responses in male and female Populus cathayana cuttings inoculated with arbuscular mycorrhizal fungi under salt

We investigated the impact of arbuscular mycorrhizal fungi (AMF) on the morphology and physiology of two genders of the typical dioecious plant Populus cathayana under salt stress. We conducted a pot experiment containing seedlings of the two genders that were subjected to salt or non-salt and filled with soil that was either inoculated with Rhizophagus intraradices or not. The results showed that males had higher mycorrhizal dependency than females. Salt stress decreased growth, the relative water content and chlorophyll fluorescence. Meanwhile, salt increased the superoxide radical (O₂⁻), and hydrogen peroxide (H₂O₂) contents and antioxidant enzyme activities. Mycorrhizal male seedlings performed better than females in shoot morphological growth under both conditions and in chlorophyll fluorescence parameters, O₂⁻ and H₂O₂ contents, MDA concentration, proline content and antioxidant enzymes activities under salt stress. In females, under saline conditions, a lower MDA concentration and H₂O₂, O₂⁻ and proline contents were observed in the leaves and roots. In addition, inoculated female plants performed better in chlorophyll fluorescence parameters than non-inoculated plants. AMF inoculation had either slight or no effects on the performance of females. These findings suggested that when subjected to stress and AMF, differences in the genders existed, followed by the alleviation of the damage to P. cathayana by AMF via improving growth and photosynthesis and antioxidant systems under salt stress.

Mitigation of adverse effects of heat stress on Vicia faba by exogenous application of magnesium

The effects of magnesium (Mg) supplementation on the growth performance, oxidative damage, DNA damage, and photosynthetic pigment synthesis, as well as on the activity level of carbonic anhydrase (CA), ribulose-1,5-bisphosphate carboxylase (Rubisco), and antioxidant enzymes were studied in Vicia faba L. plants exposed to heat stress (HS) and non-heat-stress (non-HS) conditions. Seeds were grown in pots containing a 1:1 mixture of sand and peat, with Mg treatments. The treatments consisted of (i) 0 Mg and non-HS (ambient temperature; control); (ii) 50 mM Mg; (iii) HS (38 °C); and (iv) 50 mM Mg and HS (38 °C). HS was imposed by placing potted plants in an incubator at 38 °C for 48 h. Growth attributes, total chlorophyll (Total Chl), and CA, and Rubisco activity decreased in plants subjected to HS, whereas accumulation of organic solutes [proline (Pro) and glycine betaine (GB)]; superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activity; DNA damage; electrolyte leakage (EL); and malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) content all increased. Application of Mg, however, significantly enhanced further proline (Pro), glycinebetaine (GB), SOD, POD, and CAT activity, and decreased DNA damage, EL, and MDA and H₂O₂ concentrations. These results suggest that adequate supply of Mg is not only essential for plant growth and development, but also improves plant tolerance to HS by suppressing cellular damage induced by reactive oxygen species through the enhancement of the accumulation of Pro and GB, and the actions of antioxidant enzymes.

The enhancement of tolerance to salt and cold stresses by modifying the redox state and salicylic acid content via the cytosolic malate dehydrogenase gene in transgenic apple plants

In this study, we characterized the role of an apple cytosolic malate dehydrogenase gene (MdcyMDH) in the tolerance to salt and cold stresses and investigated its regulation mechanism in stress tolerance. The MdcyMDH transcript was induced by mild cold and salt treatments, and MdcyMDH-overexpressing apple plants possessed improved cold and salt tolerance compared to wild-type (WT) plants. A digital gene expression tag profiling analysis revealed that MdcyMDH overexpression largely altered some biological processes, including hormone signal transduction, photosynthesis, citrate cycle and oxidation-reduction. Further experiments verified that MdcyMDH overexpression modified the mitochondrial and chloroplast metabolisms and elevated the level of reducing power, primarily caused by increased ascorbate and glutathione, as well as the increased ratios of ascorbate/dehydroascorbate and glutathione/glutathione disulphide, under normal and especially stress conditions. Concurrently, the transgenic plants produced a high H2 O2 content, but a low O2·- production rate was observed compared to the WT plants. On the other hand, the transgenic plants accumulated more free and total salicylic acid (SA) than the WT plants under normal and stress conditions. Taken together, MdcyMDH conferred the transgenic apple plants a higher stress tolerance by producing more reductive redox states and increasing the SA level; MdcyMDH could serve as a target gene to genetically engineer salt- and cold-tolerant trees.

Lead uptake increases drought tolerance of wild type and transgenic poplar (Populus tremula x P. alba) overexpressing gsh 1

Growth and development of plants largely depends on their adaptation ability in a changing climate. This is particularly true on heavy metal contaminated soils, but the interaction of heavy metal stress and climate on plant performance has not been intensively investigated. The aim of the present study was to elucidate if transgenic poplars (Populus tremula x P. alba) with enhanced glutathione content possess an enhanced tolerance to drought and lead (Pb) exposure (single and in combination) and if they are good candidates for phytoremediation of Pb contaminated soil. Lead exposure reduced growth and biomass accumulation only in above-ground tissue of wild type poplar, although most of lead accumulated in the roots. Drought caused a decline of the water content rather than reduced biomass production, while Pb counteracted this decline in the combined exposure. Apparently, metals such as Pb possess a protective function against drought, because they interact with abscisic acid dependent stomatal closure. Lead exposure decreased while drought increased glutathione content in leaves of both plant types. Lead accumulation was higher in the roots of transgenic plants, presumably as a result of chelation by glutathione. Water deprivation enhanced Pb accumulation in the roots, but Pb was subject to leakage out of the roots after re-watering. Transgenic plants showed better adaptation under mild drought plus Pb exposure partially due to improved glutathione synthesis. However, the transgenic plants cannot be considered as a good candidate for phytoremediation of Pb, due to its small translocation to the shoots and its leakage out of the roots upon re-watering.