Glutathione homeostasis and redox-regulation by sulfhydryl groups

Sulfur metabolism under stress: Oxidized glutathione inhibits methionine biosynthesis by destabilizing the enzyme cystathionine γ-synthase

Cysteine is the precursor for the biosynthesis of glutathione, a key stress-protective metabolite, and methionine, which is imperative for cell growth and protein synthesis. The exact mechanism that governs the routing of cysteine toward glutathione or methionine during stresses remains unclear. Our study reveals that under oxidative stress, methionine and glutathione compete for cysteine and that the increased oxidized glutathione (GSSG) levels under stress hinder methionine biosynthesis. Moreover, we find that inhibition occurs as GSSG binds to and accelerates the degradation of cystathionine γ-synthase, a key enzyme in the methionine synthesis pathway. Consequently, this leads to a reduction in the flux toward methionine-derived metabolites and redirects cysteine utilization toward glutathione, thereby enhancing plant protection. Our study suggests a novel regulatory feedback loop involving glutathione, methionine, and cysteine, shedding light on the plant stress response and the adaptive rerouting of cysteine. These findings offer new insights into the intricate balance of growth and protection in plants and its impact on their nutritional value due to low methionine levels under stress.

L-Cysteine: A promising nutritional supplement for alleviating anxiety disorders

Anxiety disorders are prevalent chronic psychological disease with complex pathogenic mechanisms. Current anxiolytics have limited efficacy and numerous side effects in many anxiety patients, highlighting the urgent need for new therapies. Recent research has been focusing on nutritional supplements, particularly amino acids, as potential therapies for anxiety disorders. Among these, L-Cysteine plays a crucial role in various biological processes. L-Cysteine exhibits antioxidant properties that can enhance the antioxidant functions of the central nervous system (CNS). Furthermore, metabolites of L-cysteine, such as glutathione and hydrogen sulfide have been shown to alleviate anxiety through distinct molecular mechanisms. Long-term administration of L-Cysteine has anxiolytic, antidepressant, and memory-improving effects. L-Cysteine depletion can lead to increased oxidative stress in the brain. This review delves into the potential mechanisms of L-Cysteine and its main products, glutathione (GSH) and hydrogen sulfide (H2S) in the management of anxiety and related diseases.

Anion exchanger1 (AE1/SLC4A1) function is impaired in red blood cells from prediabetic subjects: Potential benefits of finger lime (Citrus australasica, Faustrime cultivar) juice extract

Prediabetes is a risk state that defines a high chance of developing diabetes and cardiovascular disease. Oxidative stress mediated by hyperglycemia-induced production of reactive species could play a crucial role in this context. In the present study, we investigated whether the anion exchange capability mediated by AE1 (SLC4A1), which is sensitive to oxidative stress, was altered in human red blood cells (RBCs) obtained from prediabetic volunteers. In addition, we assessed the precise composition of bioactive compounds and the potential benefits of finger lime juice extract (Citrus australasica, Faustrime cultivar) in counteracting oxidative stress-related functional alterations. Human RBCs from normal and prediabetic volunteers were incubated with 50 µg/mL juice extract for 2 h at 25°C. Juice extract restored alterations of the anion exchange capability mediated by AE1 and prevented the structural rearrangements of AE1 and α/β-spectrin in prediabetic RBCs. AE1 functional and structural alterations were not associated with an increase in lipid peroxidation or protein oxidation at the level of the plasma membrane. An increased production of intracellular ROS, which provoked the oxidation of hemoglobin to methemoglobin, both reverted by juice extract, was instead observed. Importantly, juice extract also induced a reduction in glycated hemoglobin levels in prediabetic RBCs. Finally, juice extract blunted the overactivation of the endogenous antioxidant enzymes catalase and superoxide dismutase and prevented glutathione depletion in prediabetic RBCs. These findings contribute to clarifying cellular and molecular mechanisms related to oxidative stress and glycation events that may influence RBC and systemic homeostasis in prediabetes, identify AE1 as a sensitive biomarker of RBC structural and function alterations in prediabetes and propose finger lime juice extract as a natural antioxidant for the treatment and/or prevention of the complications associated with the prediabetic condition.

Comparison of Tumour-Specific Phenotypes in Human Primary and Expandable Pancreatic Cancer Cell Lines

There is an ongoing need for patient-specific chemotherapy for pancreatic cancer. Tumour cells isolated from human tissues can be used to predict patients' response to chemotherapy. However, the isolation and maintenance of pancreatic cancer cells is challenging because these cells become highly vulnerable after losing the tumour microenvironment. Therefore, we investigated whether the cells retained their original characteristics after lentiviral transfection and expansion. Three human primary pancreatic cancer cell lines were lentivirally transduced to create expandable (Ex) cells which were then compared with primary (Pri) cells. No obvious differences in the morphology or epithelial-mesenchymal transition (EMT) were observed between the primary and expandable cell lines. The two expandable cell lines showed higher proliferation rates in the 2D and 3D models. All three expandable cell lines showed attenuated migratory ability. Differences in gene expression between primary and expandable cell lines were then compared using RNA-Seq data. Potential target drugs were predicted by differentially expressed genes (DEGs), and differentially expressed pathways (DEPs) related to tumour-specific characteristics such as proliferation, migration, EMT, drug resistance, and reactive oxygen species (ROS) were investigated using the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. We found that the two expandable cell lines expressed similar chemosensitivity and redox-regulatory capability to gemcitabine and oxaliplatin in the 2D model as compared to their counterparts. In conclusion, we successfully generated expandable primary pancreatic cancer cell lines using lentiviral transduction. These expandable cells not only retain some tumour-specific biological traits of primary cells but also show an ongoing proliferative capacity, thereby yielding sufficient material for drug response assays, which may provide a patient-specific platform for chemotherapy drug screening.

Comparison of Reactive Sites in 2(1H)-Quinolone Derivatives for the Detection of Biologically Important Sulfur Compounds

Novel fluorescent probes based on 2(1H)-quinolone skeleton containing a malonate group (Q1-Q3) were synthesized and proposed for biothiols detection. Their chemical reactivity toward thiols was compared to the reactivity of derivative having a dicyanovinyl group (Q4) as a reactive site. The detailed photophysical properties of these compounds were assessed through the determination of absorption and fluorescence spectra, fluorescence quantum yield, and fluorescence lifetime. In the presence of biothiols, an increase in the fluorescence intensity of compounds Q1-Q3 and a hypsochromic shift in their emission bands were observed. In contrast, the compound with the dicyanovinyl group (Q4) in the presence of biothiols and cyanide ion showed the quenching of fluorescence, while a fluorescence "turn on" effect was observed toward reactive sulfur species.

Quantification of glutathione with high throughput live-cell imaging

Reduction oxidation (redox) reactions are central in life and altered redox state is associated with a spectrum of human diseases. Glutathione (GSH) is the most abundant antioxidant in eukaryotic cells and plays critical roles in maintaining redox homeostasis. Thus, measuring intracellular GSH level is an important method to assess the redox state of organism. The currently available GSH probes are based on irreversible chemical reactions with glutathione and can't monitor the real-time glutathione dynamics. Our group developed the first reversible reaction based fluorescent probe for glutathione, which can measure glutathione levels at high resolution using a confocal microscope and in the bulk scale with a flow cytometry. Most importantly it can quantitatively monitor the real-time GSH dynamics in living cells. Using the 2 ^nd generation of GSH probe, RealThiol (RT), this study measured the GSH level in living Hela cells after treatment with varying concentrations of DL-Buthionine sulfoximine (BSO) which inhibits GSH synthesis, using a high throughput imaging system, Cytation™ 5 cell imaging reader. The results revealed that GSH probe RT at the concentration of 2.0 µM accurately monitored the BSO treatment effect on GSH level in the Hela cells. The present results demonstrated that the GSH probe RT is sensitive and precise in GSH measurement in living cells at a high throughput imaging platform and has the potential to be applied to any cell lines.

The Application of Sulfur Influences Microbiome of Soybean Rhizosphere and Nutrient-Mobilizing Bacteria in Andosol

This study aimed to determine the effect of sulfur (S) application on a root-associated microbial community resulting in a rhizosphere microbiome with better nutrient mobilizing capacity. Soybean plants were cultivated with or without S application, the organic acids secreted from the roots were compared. High-throughput sequencing of 16S rRNA was used to analyze the effect of S on microbial community structure of the soybean rhizosphere. Several plant growth-promoting bacteria (PGPB) isolated from the rhizosphere were identified that can be harnessed for crop productivity. The amount of malic acid secreted from the soybean roots was significantly induced by S application. According to the microbiota analysis, the relative abundance of Polaromonas, identified to have positive association with malic acid, and arylsulfatase-producing Pseudomonas, were increased in S-applied soil. Burkholderia sp. JSA5, obtained from S-applied soil, showed multiple nutrient-mobilizing traits among the isolates. In this study, S application affected the soybean rhizosphere bacterial community structure, suggesting the contribution of changing plant conditions such as in the increase in organic acid secretion. Not only the shift of the microbiota but also isolated strains from S-fertilized soil showed PGPB activity, as well as isolated bacteria that have the potential to be harnessed for crop productivity.

An Approach to Evaluate Pb Tolerance and Its Removal Mechanisms by Pleurotus opuntiae

Widespread lead (Pb) contamination prompts various environmental problems and accounts for about 1% of the global disease burden. Thus, it has necessitated the demand for eco-friendly clean-up approaches. Fungi provide a novel and highly promising approach for the remediation of Pb-containing wastewater. The current study examined the mycoremediation capability of a white rot fungus, P. opuntiae, that showed effective tolerance to increasing concentrations of Pb up to 200 mg L−1, evidenced by the Tolerance Index (TI) of 0.76. In an aqueous medium, the highest removal rate (99.08%) was recorded at 200 mg L−1 whereas intracellular bioaccumulation also contributed to the uptake of Pb in significant amounts with a maximum of 24.59 mg g−1. SEM was performed to characterize the mycelium, suggesting changes in the surface morphology after exposure to high Pb concentrations. LIBS indicated a gradual change in the intensity of some elements after exposure to Pb stress. FTIR spectra displayed many functional groups including amides, sulfhydryl, carboxyl, and hydroxyl groups on the cell walls that led to binding sites for Pb and indicated the involvement of these groups in biosorption. XRD analysis unveiled a mechanism of biotransformation by forming a mineral complex as PbS from Pb ion. Further, Pb fostered the level of proline and MDA at a maximum relative to the control, and their concentration reached 1.07 µmol g−1 and 8.77 nmol g−1, respectively. High Pb concentration results in oxidative damage by increasing the production of ROS. Therefore, the antioxidant enzyme system provides a central role in the elimination of active oxygen. The enzymes, namely SOD, POD, CAT, and GSH, served as most responsive to clear away ROS and lower the stress. The results of this study suggested that the presence of Pb caused no visible adverse symptoms in P. opuntiae. Moreover, biosorption and bioaccumulation are two essential approaches involved in Pb removal by P. opuntiae and are established as worthwhile agents for the remediation of Pb from the environment.

Physiological response of adult Salix aurita in wetland vegetation affected by flooding with As-rich fine pyrite particles

An uncontrolled, natural episode of flooding with waters contaminated with As-rich pyrite (FeAsS) particles caused serious ecological damage leading to necrosis of plants growing in a fresh wet meadow located in an area characterized by unique geological structures rich in arsenopyrites. One of the few plant species capable of surviving this event was Salix aurita L., which grew in numbers in the analyzed area, but individual plants were affected differently by toxic flooding. No significant phenotypic changes (Group I), through partial leaf and/or stem necrosis (Group II) up to necrosis of the whole parental plant and root suckers (Group III), were observed for various willow clumps. These varied phenotypic responses of S. aurita to As-rich sediments were compared with the biochemical status of the foliage of willow trees, and with their rhizosphere physiological parameters. Our in situ study revealed that the biochemical status of leaves reflects the phenotypic damage incurred by adult willows growing in their natural environment and affected by the flooding. In leaves of willows with increasingly negative phenotypic changes (Groups I → II → III) as well as increasing levels of reactive oxygen species, malondialdehyde and decreased levels of glutathione and thiol groups were detected. Phytochelatins, commonly considered major As chelators, were not detected in S. aurita leaves. Despite a decrease in the size of leaves with the intensity of tree damage, all leaves expressed a normal level of leaf pigments. Phenotypic changes observed for particular willow clumps were only partly related to soil As levels. Moreover, As and S (but not Fe) foliar levels were related but did not correspond strictly with foliar biochemical features, or with soil As levels, soil pH or soil microbial activity, with the latter two drastically decreased in the rhizospheres of willows from Groups II and III.

Blocking xCT and PI3K/Akt pathway synergized with DNA damage of Riluzole-Pt(IV) prodrugs for cancer treatment

Cancer treatment requires the participation of multiple targets/pathways, and single approach is hard to effectively curb the proliferation and metastasis of carcinoma cells. In this work, we conjugated FDA-approved riluzole and platinum(II) drugs into a series of unreported riluzole-Pt(IV) compounds, which were designed to simultaneously target DNA, the solute carrier family 7 member 11 (SLC7A11, xCT), and the human ether a go-go related gene 1 (hERG1), to exert synergistic anticancer effect. Among them, c,c,t-[PtCl₂(NH₃)₂(OH)(glutarylriluzole)] (compound 2) displayed excellent antiproliferative activity with IC₅₀ value of 300-times lower than that of cisplatin in HCT-116, and optimal selectivity index between carcinoma and human normal liver cells (LO2). Mechanism studies indicated that compound 2 released riluzole and active Pt(II) species after entering cells to exhibit a prodrug behavior against cancer, which obviously increased DNA-damage and cell apoptosis, as well as suppressed metastasis in HCT-116. Compound 2 persisted in the xCT-target of riluzole and blocked the biosynthesis of glutathione (GSH) to trigger oxidative stress, which could boost the killing to cancer cells and reduce Pt-drug resistance. Meanwhile, compound 2 significantly inhibited invasion and metastasis of HCT-116 cells by targeting hERG1 to interrupt the phosphorylation of phosphatidylinositide 3-kinases/proteinserine-threonine kinase (PI3K/Akt), and reverse epithelial-mesenchymal transformation (EMT). Based on our results, the riluzole-Pt(IV) prodrugs studied in this work could be regarded as a new class of very promising candidates for cancer treatment compared to traditional platinum drugs.

Transcriptome and Metabolome Reveal the Molecular Mechanism of Barley Genotypes Underlying the Response to Low Nitrogen and Resupply

Nitrogen is one of the most important mineral elements for plant growth and development. Excessive nitrogen application not only pollutes the environment, but also reduces the quality of crops. However, are few studies on the mechanism of barley tolerance to low nitrogen at both the transcriptome and metabolomics levels. In this study, the nitrogen-efficient genotype (W26) and the nitrogen-sensitive genotype (W20) of barley were treated with low nitrogen (LN) for 3 days and 18 days, then treated with resupplied nitrogen (RN) from 18 to 21 days. Later, the biomass and the nitrogen content were measured, and RNA-seq and metabolites were analyzed. The nitrogen use efficiency (NUE) of W26 and W20 treated with LN for 21 days was estimated by nitrogen content and dry weight, and the values were 87.54% and 61.74%, respectively. It turned out to have a significant difference in the two genotypes under the LN condition. According to the transcriptome analysis, 7926 differentially expressed genes (DEGs) and 7537 DEGs were identified in the leaves of W26 and W20, respectively, and 6579 DEGs and 7128 DEGs were found in the roots of W26 and W20, respectively. After analysis of the metabolites, 458 differentially expressed metabolites (DAMs) and 425 DAMs were found in the leaves of W26 and W20, respectively, and 486 DAMs and 368 DAMs were found in the roots of W26 and W20, respectively. According to the KEGG joint analysis of DEGs and DAMs, it was discovered that glutathione (GSH) metabolism was the pathway of significant enrichment in the leaves of both W26 and W20. In this study, the metabolic pathways of nitrogen metabolism and GSH metabolism of barley under nitrogen were constructed based on the related DAMs and DEGs. In leaves, GSH, amino acids, and amides were the main identified DAMs, while in roots, GSH, amino acids, and phenylpropanes were mainly found DAMs. Finally, some nitrogen-efficient candidate genes and metabolites were selected based on the results of this study. The responses of W26 and W20 to low nitrogen stress were significantly different at the transcriptional and metabolic levels. The candidate genes that have been screened will be verified in future. These data not only provide new insights into how barley responds to LN, but also provide new directions for studying the molecular mechanisms of barley under abiotic stress.

Flipping Off and On the Redox Switch in the Microcirculation

Resistance arteries and arterioles evolved as specialized blood vessels serving two important functions: (a) regulating peripheral vascular resistance and blood pressure and (b) matching oxygen and nutrient delivery to metabolic demands of organs. These functions require control of vessel lumen cross-sectional area (vascular tone) via coordinated vascular cell responses governed by precise spatial-temporal communication between intracellular signaling pathways. Herein, we provide a contemporary overview of the significant roles that redox switches play in calcium signaling for orchestrated endothelial, smooth muscle, and red blood cell control of arterial vascular tone. Three interrelated themes are the focus: (a) smooth muscle to endothelial communication for vasoconstriction, (b) endothelial to smooth muscle cell cross talk for vasodilation, and (c) oxygen and red blood cell interregulation of vascular tone and blood flow. We intend for this thematic framework to highlight gaps in our current knowledge and potentially spark interest for cross-disciplinary studies moving forward.

Catalytic System for Aerobic Oxidation That Simultaneously Functions as Its Own Redox Buffer

The control of the solution electrochemical potential as well as pH impacts products in redox reactions, but the former gets far less attention. Redox buffers facilitate the maintenance of potentials and have been noted in diverse cases, but they have not been a component of catalytic systems. We report a catalytic system that contains its own built-in redox buffer. Two highly synergistic components (a) the tetrabutylammonium salt of hexavanadopolymolybdate TBA₄H₅[PMo₆V₆O₄₀] (PV₆Mo₆) and (b) Cu(ClO₄)₂ in acetonitrile catalyze the aerobic oxidative deodorization of thiols by conversion to the corresponding nonodorous disulfides at 23 °C (each catalyst alone is far less active). For example, the reaction of 2-mercaptoethanol with ambient air gives a turnover number (TON) = 3 × 10² in less than one hour with a turnover frequency (TOF) of 6 × 10^-2 s^-1 with respect to PV₆Mo₆. Multiple electrochemical, spectroscopic, and other methods establish that (1) PV₆Mo₆, a multistep and multielectron redox buffering catalyst, controls the speciation and the ratio of Cu(II)/Cu(I) complexes and thus keeps the solution potential in different narrow ranges by involving multiple POM redox couples and simultaneously functions as an oxidation catalyst that receives electrons from the substrate; (2) Cu catalyzes two processes simultaneously, oxidation of the RSH by PV₆Mo₆ and reoxidation of reduced PV₆Mo₆ by O₂; and (3) the analogous polytungstate-based system, TBA₄H₅[PW₆V₆O₄₀] (PV₆W₆), has nearly identical cyclic voltammograms (CV) as PV₆Mo₆ but has almost no catalytic activity: it does not exhibit self-redox buffering.

Glutathione contributes to plant defence against parasitic cyst nematodes

Cyst nematodes (CNs) are an important group of root-infecting sedentary endoparasites that severely damage many crop plants worldwide. An infective CN juvenile enters the host's roots and migrates towards the vascular cylinder, where it induces the formation of syncytial feeding cells, which nourish the CN throughout its parasitic stages. Here, we examined the role of glutathione (l-γ-glutamyl-l-cysteinyl-glycine) in Arabidopsis thaliana on infection with the CN Heterodera schachtii. Arabidopsis lines with mutations pad2, cad2, or zir1 in the glutamate-cysteine ligase (GSH1) gene, which encodes the first enzyme in the glutathione biosynthetic pathway, displayed enhanced CN susceptibility, but susceptibility was reduced for rax1, another GSH1 allele. Biochemical analysis revealed differentially altered thiol levels in these mutants that was independent of nematode infection. All glutathione-deficient mutants exhibited impaired activation of defence marker genes as well as genes for biosynthesis of the antimicrobial compound camalexin early in infection. Further analysis revealed a link between glutathione-mediated plant resistance to CN infection and the production of camalexin on nematode infection. These results suggest that glutathione levels affect plant resistance to CN by fine-tuning the balance between the cellular redox environment and the production of compounds related to defence against infection.

Impact of Ferrous Sulfate on Thylakoidal Multiprotein Complexes, Metabolism and Defence of Brassica juncea L. under Arsenic Stress

Forty-day-old Brassica juncea (var. Pusa Jai Kisan) plants were exposed to arsenic (As, 250 µM Na2HAsO4·7H2O) stress. The ameliorative role of ferrous sulfate (2 mM, FeSO4·7H2O, herein FeSO4) was evaluated at 7 days after treatment (7 DAT) and 14 DAT. Whereas, As induced high magnitude oxidative stress, FeSO4 limited it. In general, As decreased the growth and photosynthetic parameters less when in the presence of FeSO4. Furthermore, components of the antioxidant system operated in better coordination with FeSO4. Contents of non-protein thiols and phytochelatins were higher with the supply of FeSO4. Blue-Native polyacrylamide gel electrophoresis revealed an As-induced decrease in almost every multi-protein-pigment complex (MPC), and an increase in PSII subcomplex, LHCII monomers and free proteins. FeSO4 supplication helped in the retention of a better stoichiometry of light-harvesting complexes and stabilized every MPC, including supra-molecular complexes, PSI/PSII core dimer/ATP Synthase, Cytochrome b6/f dimer and LHCII dimer. FeSO4 strengthened the plant defence, perhaps by channelizing iron (Fe) and sulfur (S) to biosynthetic and anabolic pathways. Such metabolism could improve levels of antioxidant enzymes, and the contents of glutathione, and phytochelatins. Important key support might be extended to the chloroplast through better supply of Fe-S clusters. Therefore, our results suggest the importance of both iron and sulfur to combat As-induced stress in the Indian mustard plant at biochemical and molecular levels through enhanced antioxidant potential and proteomic adjustments in the photosynthetic apparatus.

Environmental and Production Aspects of Using Fertilizers Based on Waste Elemental Sulfur and Organic Materials

Crop fertilization with sulfur is an important part of agricultural practices, as is the systematic increase in soil organic matter content. Materials of waste origin constitute a source of plant-available sulfur, as well as soil organic matter. The study was to verify the hypothesis assuming that combining waste sulfur pulp and its mixtures with organic materials enables simultaneous soil enrichment with readily available sulfur and organic matter. A 240-day incubation experiment was conducted, on two soils: very light and heavy; with two sulfur doses applied to each soil (20 and 40 mg S/kg d.m. for very light soil, and 30 and 60 mg S/kg d.m. for heavy soil). The sulfate sulfur content in the incubated soil material, treated with the addition of sulfur pulp and its mixtures with organic materials, increased significantly up to day 60 and then decreased. The application of these materials significantly increased the content of available sulfur and decreased the pH value of the incubated material. The effect of the introduced materials on dehydrogenase activity depended on soil granulometric composition (the impact of the applied materials on the activity of these enzymes in very light soil was small, and in heavy soil, their activity was usually limited by the presence of introduced materials). Application of the studied materials had little effect on the total organic carbon content in the incubated soil material (a significant change in the value of this parameter, in relation to the control soil, was recorded in some treatments of heavy soil).

Glutamate: A multifunctional amino acid in plants

Glutamate (Glu) is a versatile metabolite and a signaling molecule in plants. Glu biosynthesis is associated with the primary nitrogen assimilation pathway. The conversion between Glu and 2-oxoglutarate connects Glu metabolism to the tricarboxylic acid cycle, carbon metabolism, and energy production. Glu is the predominant amino donor for transamination reactions in the cell. In addition to protein synthesis, Glu is a building block for tetrapyrroles, glutathione, and folate. Glu is the precursor of γ-aminobutyric acid that plays an important role in balancing carbon/nitrogen metabolism and various cellular processes. Glu can conjugate to the major auxin indole 3-acetic acid (IAA), and IAA-Glu is destined for oxidative degradation. Glu also conjugates with isochorismate for the production of salicylic acid. Accumulating evidence indicates that Glu functions as a signaling molecule to regulate plant growth, development, and defense responses. The ligand-gated Glu receptor-like proteins (GLRs) mediate some of these responses. However, many of the Glu signaling events are GLR-independent. The receptor perceiving extracellular Glu as a danger signal is still unknown. In addition to GLRs, Glu may act on receptor-like kinases or receptor-like proteins to trigger immune responses. Glu metabolism and Glu signaling may entwine to regulate growth, development, and defense responses in plants.

Antioxidant enzyme responses and metabolite functioning of Pisum sativum L. to sewage sludge in arid and semi-arid environments

The productivity of plants is a direct variant of the countless biotic and abiotic stresses to which a plant is exposed in an environment. This study aimed to investigate the capabilities of leguminous plant garden pea (Pisum sativum L.) to resist water deficit conditions in arid and semi-arid areas when applied with varied doses of sludge for growth response. The effect of sludge doses was evaluated on crop yield, antioxidant enzymes, viz., ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), superoxide dismutase (SOD), and glutathione reductase (GR), and metabolites (ascorbic acid, glutathione, and total protein content). The effective sludge concentrations with respect to seed weight and crop yield were found to be in the following trend: D2 (6.25%)>D3 (12.5%)>D1 (2.5%)>D0 (control) under organic amendment (OA). Conversely, a high dose of the sludge reduced the seed weight and total crop yield. The sludge doses D2 under arid and semi-arid conditions along with organic amendments (OA) significantly enhance the antioxidant enzyme activity, whereas sludge dose D3 with OA ominously regulates the activity of these enzymes. Besides, seeds depicted a considerable increase in ascorbic acid, glutathione, and total protein content in arid and semi-arid conditions upon the application of sludge with OA. Sewage sludge as a source of nutrients indirectly enhances crop yield, antioxidant enzymes, and antioxidant metabolites. Thus, it improves the defense mechanism, reduces abnormal protein glycation, and depletes the susceptibility of protein to proteolysis.

Histone Deacetylation Controls Xylem Vessel Cell Differentiation via Transcriptional Regulation of a Transcription Repressor Complex OFP1/4-MYB75-KNAT7-BLH6

Xylem vessels are indispensable tissues in vascular plants that transport water and minerals. The differentiation of xylem vessel cells is characterized by secondary cell wall deposition and programmed cell death. These processes are initiated by a specific set of transcription factors, called VASCULAR-RELATED NAC-DOMAIN (VND) family proteins, through the direct and/or indirectly induction of genes required for secondary cell wall deposition and programmed cell death. In this study, we explored novel regulatory factors for xylem vessel cell differentiation in Arabidopsis thaliana. We tested the effects of cellular stress inducers on VND7-induced differentiation of xylem vessel cells with the VND7-VP16-GR system, in which VND7 activity is post-translationally induced by dexamethasone application. We established that the histone deacetylase (HDAC) inhibitors trichostatin A (TSA) and sirtinol inhibited VND7-induced xylem vessel cell differentiation. The inhibitory effects of TSA and sirtinol treatment were detected only when they were added at the same time as the dexamethasone application, suggesting that TSA and sirtinol mainly influence the early stages of xylem vessel cell differentiation. Expression analysis revealed that these HDAC inhibitors downregulated VND7-downstream genes, including both direct and indirect targets of transcriptional activation. Notably, the HDAC inhibitors upregulated the transcript levels of negative regulators of xylem vessel cells, OVATE FAMILY PROTEIN1 (OFP1), OFP4, and MYB75, which are known to form a protein complex with BEL1-LIKE HOMEODOMAIN6 (BLH6) to repress gene transcription. The KDB system, another in vitro induction system of ectopic xylem vessel cells, demonstrated that TSA and sirtinol also inhibited ectopic formation of xylem vessel cells, and this inhibition was partially suppressed in knat7-1, bhl6-1, knat7-1 bhl6-1, and quintuple ofp1 ofp2 ofp3 ofp4 ofp5 mutants. Thus, the negative effects of HDAC inhibitors on xylem vessel cell differentiation are mediated, at least partly, by the abnormal upregulation of the transcriptional repressor complex OFP1/4-MYB75-KNAT7-BLH6. Collectively, our findings suggest that active regulation of histone deacetylation by HDACs is involved in xylem vessel cell differentiation via the OFP1/4-MYB75-KNAT7-BLH6 complex.

Roles of Exogenous α-Lipoic Acid and Cysteine in Mitigation of Drought Stress and Restoration of Grain Quality in Wheat

Cysteine (Cys) and α-lipoic acid (ALA) are naturally occurring antioxidants (sulfur-containing compounds) that can protect plants against a wide spectrum of environmental stresses. However, up to now, there are no conclusive data on their integrative roles in mitigation of drought stress in wheat plants. Here, we studied the influence of ALA at 0.02 mM (grain dipping pre-cultivation treatment) and Cys (25 and 50 ppm as a foliar application) under well watered and deficit irrigation (100% and 70% of recommended dose). The results showed that deficit irrigation markedly caused obvious cellular oxidative damage as indicated by elevating the malondialdehyde (MDA) and hydrogen peroxide content (H₂O₂). Moreover, water stressed plants exhibited multiple changes in physiological metabolism, which affected the quantitative and qualitative variables of grain yield. The enzymatic antioxidants, including superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and peroxidase (POX) were improved by Cys application. SOD and APX had the same response when treated with ALA, but CAT and POX did not. Moreover, both studied molecules stimulated chlorophyll (Chl) and osmolytes' biosynthesis. In contrast, the Chl a/b ratio was decreased, while flavonoids were not affected by either of the examined molecules. Interestingly, all above-mentioned changes were associated with an improvement in the scavenging capacity of reactive oxygen species (ROS), leaf relative water content (RWC), grain number, total grain yield, weight of 1000 kernels, gluten index, falling number, and alveographic parameters (P, W, and P/L values). Furthermore, heatmap plot analysis revealed several significant correlations between different studied parameters, which may explore the importance of applied Cys and ALA as effective compounds in wheat cultivation under water deficit conditions.

Differences in Acid Stress Response of Lacticaseibacillus paracasei Zhang Cultured from Solid-State Fermentation and Liquid-State Fermentation

Liquid-state fermentation (LSF) and solid-state fermentation (SSF) are two forms of industrial production of lactic acid bacteria (LAB). The choice of two fermentations for LAB production has drawn wide concern. In this study, the tolerance of bacteria produced by the two fermentation methods to acid stress was compared, and the reasons for the tolerance differences were analyzed at the physiological and transcriptional levels. The survival rate of the bacterial agent obtained from solid-state fermentation was significantly higher than that of bacteria obtained from liquid-state fermentation after spray drying and cold air drying. However, the tolerance of bacterial cells obtained from liquid-state fermentation to acid stress was significantly higher than that from solid-state fermentation. The analysis at physiological level indicated that under acid stress, cells from liquid-state fermentation displayed a more solid and complete membrane structure, higher cell membrane saturated fatty acid, more stable intracellular pH, and more stable activity of ATPase and glutathione reductase, compared with cells from solid-state fermentation, and these physiological differences led to better tolerance to acid stress. In addition, transcriptomic analysis showed that in the cells cultured from liquid-state fermentation, the genes related to glycolysis, inositol phosphate metabolism, and carbohydrate transport were down-regulated, whereas the genes related to fatty acid synthesis and glutamate metabolism were upregulated, compared with those in cells from solid-state fermentation. In addition, some genes related to acid stress response such as cspA, rimP, rbfA, mazF, and nagB were up-regulated. These findings provide a new perspective for the study of acid stress tolerance of L. paracasei Zhang and offer a reference for the selection of fermentation methods of LAB production.

The Arbuscular Mycorrhizal Fungus Glomus viscosum Improves the Tolerance to Verticillium Wilt in Artichoke by Modulating the Antioxidant Defense Systems

Verticillium wilt, caused by the fungal pathogen Verticillium dahliae, is the most severe disease that threatens artichoke (Cynara scolymus L.) plants. Arbuscular mycorrhizal fungi (AMF) may represent a useful biological control strategy against this pathogen attack, replacing chemical compounds that, up to now, have been not very effective. In this study, we evaluated the effect of the AMF Glomus viscosum Nicolson in enhancing the plant tolerance towards the pathogen V. dahliae. The role of the ascorbate-glutathione (ASC-GSH) cycle and other antioxidant systems involved in the complex network of the pathogen-fungi-plant interaction have been investigated. The results obtained showed that the AMF G. viscosum is able to enhance the defense antioxidant systems in artichoke plants affected by V. dahliae, alleviating the oxidative stress symptoms. AMF-inoculated plants exhibited significant increases in ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), and superoxide dismutase (SOD) activities, a higher content of ascorbate (ASC) and glutathione (GSH), and a decrease in the levels of lipid peroxidation and hydrogen peroxide (H₂O₂). Hence, G. viscosum may represent an effective strategy for mitigating V. dahliae pathogenicity in artichokes, enhancing the plant defense systems, and improving the nutritional values and benefit to human health.

Stage-, sex- and tissue-related changes in H2O2, glutathione concentration, and glutathione-dependent enzymes activity in Aiolopus thalassinus (Orthoptera: Acrididae) from heavy metal polluted areas

This study is part of a large project carried out at the Cairo University, Egypt, and focused on assessing physiological and biochemical changes in Aiolopus thalassinus under the influence of environmental pollution with heavy metals (Pb, Cd, Cu, and Zn). The study aimed to investigate parameters related to maintaining redox balance, with particular emphasis on stage-, sex- and tissue-dependent differences in H₂O₂ and glutathione (GSH) levels and activity of selected enzymes involved in GSH metabolism. A noticeable increase in the concentration of H₂O₂ was found, especially in the gut of 5th instar nymphs and females from the highly polluted site. An increase in GSH concentration was significant, especially in the gut of adult A. thalassinus from the high polluted site. However, recycling of reduced form of glutathione in the gut by glutathione reductase (GR) was relevant only for females from the high polluted site. Nymphs and females generally showed higher glutathione S-transferase (GST) activity, especially in the gut. These stage- and sex-related differences can result from different growth dynamic and various reproductive functions of nymphs and both sexes. The digestive track is in direct contact with xenobiotics consumed with food. Nymphs are characterized by vigorous growth, they feed intensively, and their development processes are associated with substantial oxygen consumption. Also, maintaining the antioxidant system at a high level can be more important for females than males due to egg production over a long period. It appears that de novo GSH synthesis is a favorable and cost-effective adaptation mechanism for A. thalassinus living in the high polluted site.

Integration of MsrB1 and MsrB2 in the Redox Network during the Development of Orthodox and Recalcitrant Acer Seeds

Two related tree species, Norway maple (Acer platanoides L.) and sycamore (Acer pseudoplatanus L.), produce desiccation-tolerant (orthodox) and desiccation-sensitive (recalcitrant) seeds, respectively. We compared the seeds of these two species to characterize the developmentally driven changes in the levels of peptide-bound methionine sulfoxide (MetO) and the abundance of methionine sulfoxide reductases (Msrs) B1 and B2, with respect to the cellular redox environment. Protein oxidation at the Met level was dynamic only in Norway maple seeds, and the reduced MsrB2 form was detected only in this species. Cell redox status, characterized by the levels of reduced and oxidized ascorbate, glutathione, and nicotinamide adenine dinucleotide (NAD)/phosphate (NADP), was clearly more reduced in the Norway maple seeds than in the sycamore seeds. Clear correlations between MetO levels, changes in water content and redox status were reported in orthodox Acer seeds. The abundance of Msrs was correlated in both species with redox determinants, mainly ascorbate and glutathione. Our data suggest that MsrB2 is associated with the acquisition of desiccation tolerance and that ascorbate might be involved in the redox pathway enabling the regeneration of Msr via intermediates that are not known yet.

Overexpression of CDSP32 (GhTRX134) Cotton Gene Enhances Drought, Salt, and Oxidative Stress Tolerance in Arabidopsis

Upland cotton (Gossypium hirsutum L.) is the main natural fiber crop worldwide and is an essential source of seed oil and biofuel products. Many abiotic stresses, such as drought and salinity, constrain cotton production. Thioredoxins (TRXs) are a group of small ubiquitous proteins that are widely distributed among organisms. TRXs play a crucial role in regulating diverse functions during plant growth and development. In the present study, a novel GhTRX134 gene was characterized and overexpressed in Arabidopsis and silenced in cotton under drought stress. Furthermore, the proline content and enzyme activity levels were measured in transgenic plants and wild-type (Wt) plants under drought and salt stress. The results revealed that the overexpression of GhTRX134 enhanced abiotic stress tolerance. When GhTRX134 was silenced, cotton plants become more sensitive to drought. Taken together, these findings confirmed that the overexpression of GhTRX134 improved drought and salt tolerance in Arabidopsis plants. Therefore, the GhTRX134 gene can be transformed into cotton plants to obtain transgenic lines for more functional details.

Molecular genetic bases of seed resistance to oxidative stress during storage

Conservation of plant genetic diversity, including economically important crops, is the foundation for food safety. About 90 % of the world’s crop genetic diversity is stored as seeds in genebanks. During storage seeds suffer physiological stress consequences, one of which is the accumulation of free radicals, primarily reactive oxygen species (ROS). An increase in ROS leads to oxidative stress, which negatively affects the quality of seeds and can lead to a complete loss of their viability. The review summarizes data on biochemical processes that affect seed longevity. The data on the destructive effect of free radicals towards plant cell macromolecules are analyzed, and the ways to eliminate excessive ROS in plants, the most important of which is the glutathioneascorbate pathway, are discussed. The relationship between seed dormancy and seed longevity is examined. Studying seeds of different plant species revealed a negative correlation between seed dormancy and longevity, while various authors who researched Arabidopsis seeds reported both positive and negative correlations between dormancy and seed longevity. A negative correlation between seed dormancy and viability probably means that seeds are able to adapt to changing environmental conditions. This review provides a summary of Arabidopsis genes associated with seed viability. By now, a significant number of loci and genes affecting seed longevity have been identified. This review contains a synopsis of modern studies on the viability of barley seeds. QTLs associated with barley seed longevity were identified on chromosomes 2H, 5H and 7H. In the QTL regions studied, the Zeo1, Ale, nud, nadp-me, and HvGR genes were identified. However, there is still no definite answer as to which genes would serve as markers of seed viability in a certain plant species.

Biosynthesis of Sulfur-Containing Small Biomolecules in Plants

Sulfur is an essential element required for plant growth. It can be found as a thiol group of proteins or non-protein molecules, and as various sulfur-containing small biomolecules, including iron-sulfur (Fe/S) clusters, molybdenum cofactor (Moco), and sulfur-modified nucleotides. Thiol-mediated redox regulation has been well investigated, whereas biosynthesis pathways of the sulfur-containing small biomolecules have not yet been clearly described. In order to understand overall sulfur transfer processes in plant cells, it is important to elucidate the relationships among various sulfur delivery pathways as well as to investigate their interactions. In this review, we summarize the information from recent studies on the biosynthesis pathways of several sulfur-containing small biomolecules and the proteins participating in these processes. In addition, we show characteristic features of gene expression in Arabidopsis at the early stage of sulfate depletion from the medium, and we provide insights into sulfur transfer processes in plant cells.

Peptide-Bound Methionine Sulfoxide (MetO) Levels and MsrB2 Abundance Are Differentially Regulated during the Desiccation Phase in Contrasted Acer Seeds

Norway maple and sycamore produce desiccation-tolerant (orthodox) and desiccation-sensitive (recalcitrant) seeds, respectively. Drying affects reduction and oxidation (redox) status in seeds. Oxidation of methionine to methionine sulfoxide (MetO) and reduction via methionine sulfoxide reductases (Msrs) have never been investigated in relation to seed desiccation tolerance. MetO levels and the abundance of Msrs were investigated in relation to levels of reactive oxygen species (ROS) such as hydrogen peroxide, superoxide anion radical and hydroxyl radical (•OH), and the levels of ascorbate and glutathione redox couples in gradually dried seeds. Peptide-bound MetO levels were positively correlated with ROS concentrations in the orthodox seeds. In particular, •OH affected MetO levels as well as the abundance of MsrB2 solely in the embryonic axes of Norway maple seeds. In this species, MsrB2 was present in oxidized and reduced forms, and the latter was favored by reduced glutathione and ascorbic acid. In contrast, sycamore seeds accumulated higher ROS levels. Additionally, MsrB2 was oxidized in sycamore throughout dehydration. In this context, the three elements •OH level, MetO content and MsrB2 abundance, linked together uniquely to Norway maple seeds, might be considered important players of the redox network associated with desiccation tolerance.

Physiological, Biochemical and Reproductive Studies on Valeriana wallichii, a Critically Endangered Medicinal Plant of the Himalayan Region Grown under In-Situ and Ex-Situ Conditions

Valeriana wallichii, a perennial herb belonging to family Valerianaceae, is an important medicinal herb of the Himalayan region. The incessant exploitation of nature for meeting the demands of the pharmaceutical industry has put unbearable pressure on its natural habitats. A study on its physiological, biochemical, growth and reproductive attributes was planned. Physiological study revealed that ex-situ (outside their natural habitat) populations faced severe stress as compared to in-situ (natural habitat) plants. The difference in the performance of these habitat plants was related to superoxide and H₂O₂ in the leaves. Photosynthetic attributes were increased in in-situ populations. Proline content and its biosynthetic enzymes ornithine aminotransferase, and pyrroline-5-carboxylate reductase showed an increase in ex-situ plants; proline oxidase decreased. Glucose-6-phosphate dehydrogenase, shikimic acid dehydrogenese, phenylalanine lyase, and flavonoids content showed an increment in ex-situ plants. Antioxidants enzyme superoxide dismutase, catalase, ascorbate peroxidase and reduced glutathione showed an increment in ex-situ conditions. Growth and reproductive attributes were more in ex-situ plants. The observations made are suggestive that a comprehensive conservation programme involving in-situ as well as ex-situ strategies will be effective for the conservation and long term survival of the species.

Chromium Bioaccumulation and Its Impacts on Plants: An Overview

Chromium (Cr) is an element naturally occurring in rocky soils and volcanic dust. It has been classified as a carcinogen agent according to the International Agency for Research on Cancer. Therefore, this metal needs an accurate understanding and thorough investigation in soil-plant systems. Due to its high solubility, Cr (VI) is regarded as a hazardous ion, which contaminates groundwater and can be transferred through the food chain. Cr also negatively impacts the growth of plants by impairing their essential metabolic processes. The toxic effects of Cr are correlated with the generation of reactive oxygen species (ROS), which cause oxidative stress in plants. The current review summarizes the understanding of Cr toxicity in plants via discussing the possible mechanisms involved in its uptake, translocation and sub-cellular distribution, along with its interference with the other plant metabolic processes such as chlorophyll biosynthesis, photosynthesis and plant defensive system.

Molecular cloning of putative chloroplastic cysteine synthase in Leucaena leucocephala

Cysteine biosynthesis is directed by the successive commitments of serine acetyltransferase, and O-acetylserine (thiol) lyase (OASTL) compounds, which subsequently frame the decameric cysteine synthase complex. The isoforms of OASTL are found in three compartments of the cell: the cytosol, plastid, and mitochondria. In this investigation, we first isolated putative chloroplastic OASTL (Ch-OASTL) from Leucaena leucocephala, and the Ch-OASTL was then expressed in BL21-competent Escherichia coli. The putative Ch-OASTL cDNA clone had 1,543 base pairs with 391 amino acids in its open reading frame and a molecular weight of 41.54 kDa. The purified protein product exhibited cysteine synthesis ability, but not mimosine synthesis activity. However, they both make the common α-aminoacrylate intermediate in their first half reaction scheme with the conventional substrate O-acetyl serine (OAS). Hence, we considered putative Ch-OASTL a cysteine-specific enzyme. Kinetic studies demonstrated that the optimum pH for cysteine synthesis was 7.0, and the optimum temperature was 40 °C. In the cysteine synthesis assay, the K_m and k_cat values were 838 ± 26 µM and 72.83 s^-1 for OAS, respectively, and 60 ± 2 µM and 2.43 s^-1 for Na₂S, respectively. We can infer that putative Ch-OASTL regulatory role is considered a sensor for sulfur constraint conditions, and it acts as a forerunner of various metabolic compound molecules.

Thiol redox-regulation for efficient adjustment of sulfur metabolism in acclimation to abiotic stress

Sulfur assimilation and sulfur metabolism are tightly controlled at the transcriptional, post-transcriptional, and post-translational levels in order to meet the demand for reduced sulfur in growth and metabolism. These regulatory mechanisms coordinate the cellular sulfhydryl supply with carbon and nitrogen assimilation in particular. Redox homeostasis is an important cellular parameter intimately connected to sulfur by means of multiple thiol modifications. Post-translational thiol modifications such as disulfide formation, sulfenylation, S-nitrosylation, persulfidation, and S-glutathionylation allow for versatile switching and adjustment of protein functions. This review focuses on redox-regulation of enzymes involved in the sulfur assimilation pathway, namely adenosine 5´-phosphosulfate reductase (APR), adenosine 5´-phosphosulfate kinase (APSK), and γ-glutamylcysteine ligase (GCL). The activity of these enzymes is adjusted at the transcriptional and post-translational level depending on physiological requirements and the state of the redox and reactive oxygen species network, which are tightly linked to abiotic stress conditions. Hormone-dependent fine-tuning contributes to regulation of sulfur assimilation. Thus, the link between oxylipin signalling and sulfur assimilation has been substantiated by identification of the so-called COPS module in the chloroplast with its components cyclophilin 20-3, O-acetylserine thiol lyase, 2-cysteine peroxiredoxin, and serine acetyl transferase. We now have a detailed understanding of how regulation enables the fine-tuning of sulfur assimilation under both normal and abiotic stress conditions.

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.

Glutathione Activates Type III Secretion System Through Vfr in Pseudomonas aeruginosa

Glutathione (GSH) is the most abundant antioxidant in all living organisms. Previously, we have shown that a deletion mutant in the glutathione synthetase gene (ΔgshB) decreases the expression of type III secretion system (T3SS) genes of Pseudomonas aeruginosa. However, the mechanism remains elusive. In this study, a comprehensive transcriptomic analysis of the GSH-deficient mutant ΔgshAΔgshB was used to elucidate the role of GSH in the pathogenesis of P. aeruginosa. The data show that the expression of genes in T3SS, type VI secretion system (T6SS) and some regulatory genes were impaired. ΔgshAΔgshB was attenuated in a mouse model of acute pneumonia, swimming and swarming motilities, and biofilm formation. Under T3SS inducing conditions, GSH enhanced the expression of T3SS in both wild-type PAO1 and ΔgshAΔgshB, but not in Δvfr. Genetic complementation of Δvfr restored the ability of GSH to induce the expression of T3SS genes. Site-directed mutagenesis based substitution of cysteine residues with alanine in Vfr protein abolished the induction of T3SS genes by GSH, confirming that GSH regulates T3SS genes through Vfr. Exposure to H₂O₂ decreased free thiol content on Vfr, indicating that the protein was sensitive to redox modification. Importantly, GSH restored the oxidized Vfr to reduced state. Collectively, these results suggest that GSH serves as an intracellular redox signal sensed by Vfr to upregulate T3SS expression in P. aeruginosa. Our work provides new insights into the role of GSH in P. aeruginosa pathogenesis.

Chemical Probes for Redox Signaling and Oxidative Stress

SIGNIFICANCE

Cellular reactive oxygen species (ROS) mediate redox signaling cascades that are critical to numerous physiological and pathological processes. Analytical methods to monitor cellular ROS levels and proteomic platforms to identify oxidative post-translational modifications (PTMs) of proteins are critical to understanding the triggers and consequences of redox signaling. Recent Advances: The prevalence and significance of redox signaling has recently been illuminated through the use of chemical probes that allow for sensitive detection of cellular ROS levels and proteomic dissection of oxidative PTMs directly in living cells.

CRITICAL ISSUES

In this review, we provide a comprehensive overview of chemical probes that are available for monitoring ROS and oxidative PTMs, and we highlight the advantages and limitations of these methods.

FUTURE DIRECTIONS

Despite significant advances in chemical probes, the low levels of cellular ROS and low stoichiometry of oxidative PTMs present challenges for accurately measuring the extent and dynamics of ROS generation and redox signaling. Further improvements in sensitivity and ability to spatially and temporally control readouts are essential to fully illuminate cellular redox signaling.

GRA78 encoding a putative S-sulfocysteine synthase is involved in chloroplast development at the early seedling stage of rice

Cysteine functions not only as an amino acid in proteins but also as a precursor for a large number of essential biomolecules. Cysteine is synthesized via the incorporation of sulfide to O-acetylserine under the catalysis of O-acetylserine(thiol)lyase (OASTL). In dicotyledonous Arabidopsis, nine OASTL genes have been reported. However, in their null mutants, only the mutant of CS26 encoding S-sulfocysteine synthase showed the visible phenotypic changes, displaying significantly small plants and pale-green leaves under long-day condition but not short-day condition. Up to now, no OASTL gene or mutant has been identified in monocotyledon. In this study, we isolated a green-revertible albino mutant gra78 in rice (Oryza sativa). Its albino phenotype at the early seedling stage was sensitive to temperature but independent of photoperiod. Map-based cloning revealed that candidate gene LOC_Os01g59920 of GRA78 encodes a putative S-sulfocysteine synthase showing significant similarity with Arabidopsis CS26. Complementation experiment confirmed that mutation in LOC_Os01g59920 accounted for the mutant phenotype of gra78. GRA78 is constitutively expressed in all tissues and its encoded protein is targeted to the chloroplast. In addition, qRT-PCR suggested that expression levels of four OASTL homolog genes and five photosynthetic genes were remarkably down-regulated.

Redox-Responsive Protein Design: Design of a Small Protein Motif Dependent on Glutathionylation

Cysteine S-glutathionylation is a protein post-translational modification that promotes cellular responses to changes in oxidative conditions. The design of protein motifs that directly depend on defined changes to protein side chains provides new methods for probing diverse protein post-translational modifications. A canonical, 12-residue EF-hand motif was redesigned to be responsive to cysteine glutathionylation. The key design principle was the replacement of the metal-binding Glu12 carboxylate of an EF-hand with a motif capable of metal binding via a free carboxylate in the glutathione-conjugated peptide. In the optimized peptide (DKDADGWCG), metal binding and terbium luminescence were dependent on glutathionylation, with weaker metal binding in the presence of reduced cysteine but increased metal affinity and a 3.5-fold increase in terbium luminescence at 544 nm when cysteine was glutathionylated. Nuclear magnetic resonance spectroscopy indicated that the structure at all residues of the glutathionylated peptide changed in the presence of metal, with chemical shift changes consistent with the adoption of an EF-hand-like structure in the metal-bound glutathionylated peptide. This small protein motif consists of canonical amino acids and is thus genetically encodable, for its potential use as a localized tag to probe protein glutathionylation.

The effect of a doubled glutathione level on parameters affecting the germinability of recalcitrant Acer saccharinum seeds during drying

Approximately 20% of plant species, including silver maple (Acer saccharinum L.), produce seeds that are sensitive to desiccation, which is reflected in their poor storage potential and viability. In the search for a compound that can improve seed recalcitrance, freshly harvested seeds were soaked in either 2.5 mM reduced glutathione (GSH) or water and desiccated to comparable water levels of 55-20%. We examined the impact of a doubled endogenous level of glutathione on the seed germination capacity, the activity of enzymes involved in glutathione metabolism, the cell membrane components and integrity, reactive oxygen species, and ascorbate levels. GSH treatment resulted in slower dehydration and a higher germination capacity. The increased glutathione was mainly consumed by glutathione S-transferase, leading to more efficient detoxification, and by dehydroascorbate reductase (DHAR), accelerating the ascorbate regeneration. As a result, the cellular environment became more reduced, and protection of the membrane structures was enhanced. The ameliorated membrane integrity was manifested via a lower electrolyte leakage and a lower lipid peroxide level despite the higher level of hydrogen peroxide (H₂O₂) detected in the GSH-treated seeds. The degradation of phospholipids (PLs) was less intense and related to the phosphatidylinositol (PI) level, which is the precursor of the phospholipase D cofactor, whereas in water-soaked seeds, PL degradation was promoted by H₂O₂. The germination capacity of the dehydrated seeds depended primarily on the level of H₂O₂, lipid hydroxyperoxides, electrolyte leakage, GSH, the half-cell reduction potential of glutathione, PI, and the activity of DHAR and γ-glutamylcysteine synthetase. Interestingly, H₂O₂ affected all of the parameters. The germination of GSH-boosted seeds was strongly impacted by the pool of ascorbate, the half-cell reduction potential of ascorbate, and the glutathione peroxidase activity. In general, germination was DHAR activity-dependent. A strong negative correlation was detected in the water-soaked seeds, whereas a strong positive correlation was detected in the GSH-treated seeds. The enhanced level of glutathione likely improved the efficiency of the ascorbate-glutathione cycle, confirming its effect on seed germinability after dehydration.

Effects of the Usage of l-Cysteine (l-Cys) on Human Health

This review summarizes recent knowledge about the use of the amino acid l-Cysteine (l-Cys) through diet, nutritional supplements or drugs with the aim to improve human health or treat certain diseases. Three databases (PubMed, Scopus, and Web of Science) and different keywords have been used to create a database of documents published between 1950 and 2017 in scientific journals in English or Spanish. A total of 60,885 primary publications were ultimately selected to compile accurate information about the use of l-Cys in medicine and nutritional therapies and to identify the reported benefits of l-Cys on human health. The number of publications about the use of l-Cys for these purposes has increased significantly during the last two decades. This increase seems to be closely related to the rise of nutraceutical industries and personalized medicine. The main evidence reporting benefits of l-Cys usage is summarized. However, the lack of accurate information and studies based on clinical trials hampers consensus among authors. Thus, the debate about the role and effectiveness of supplements/drugs containing l-Cys is still open.

Glutathione limits aquacopper(I) to sub-femtomolar concentrations through cooperative assembly of a tetranuclear cluster

The tripeptide glutathione (GSH) is a crucial intracellular reductant and radical scavenger, but it may also coordinate the soft Cu(I) cation and thereby yield pro-oxidant species. The GSH-Cu(I) interaction is thus a key consideration for both redox and copper homeostasis in cells. However, even after nearly four decades of investigation, the nature and stability of the GSH-Cu(I) complexes formed under biologically relevant conditions remain controversial. Here, we revealed the unexpected predominance of a tetranuclear [Cu₄(GS)₆] cluster that is sufficiently stable to limit the effective free aquacopper(I) concentration to the sub-femtomolar regime. Combined spectrophotometric-potentiometric titrations at biologically realistic GSH/Cu(I) ratios, enabled by our recently developed Cu(I) affinity standards and corroborated by low-temperature phosphorescence studies, established cooperative assembly of [Cu₄(GS)₆] as the dominant species over a wide pH range, from 5.5 to 7.5. Our robust model for the glutathione-Cu(I) equilibrium system sets a firm upper limit on the thermodynamic availability of intracellular copper that is 3 orders of magnitude lower than previously estimated. Taking into account their ability to catalyze the production of deleterious superoxide, the formation of Cu(I)-glutathione complexes might be avoided under normal physiological conditions. The actual intracellular Cu(I) availability may thus be regulated a further 3 orders of magnitude below the GSH/Cu(I) affinity limit, consistent with the most recent affinity determinations of Cu(I) chaperones.

Quantitative assessment of specific carbonic anhydrase inhibitors effect on hypoxic cells using electrical impedance assays

Carbonic anhydrase IX (CA IX) is an important orchestrator of hypoxic tumour environment, associated with tumour progression, high incidence of metastasis and poor response to therapy. Due to its tumour specificity and involvement in associated pathological processes: tumourigenesis, angiogenesis, inhibiting CA IX enzymatic activity has become a valid therapeutic option. Dynamic cell-based biosensing platforms can complement cell-free and end-point analyses and supports the process of design and selection of potent and selective inhibitors. In this context, we assess the effectiveness of recently emerged CA IX inhibitors (sulphonamides and sulphocoumarins) and their antitumour potential using an electrical impedance spectroscopy biosensing platform. The analysis allows discriminating between the inhibitory capacities of the compounds and their inhibition mechanisms. Microscopy and biochemical assays complemented the analysis and validated impedance findings establishing a powerful biosensing tool for the evaluation of carbonic anhydrase inhibitors potency, effective for the screening and design of anticancer pharmacological agents.

Proteomic analysis of S-nitrosylated and S-glutathionylated proteins in wheat seedlings with different dehydration tolerances

A loss of dehydration tolerance in wheat seedlings on the fifth day following imbibition is associated with a disturbance in cellular redox homeostasis, as documented by a shift of the reduced/oxidized glutathione ratio to a more oxidized state and a significant increase in the ratio of protein thiols to the total thiol group content. Therefore, the identification and characterization of redox-sensitive proteins are important steps toward understanding the molecular mechanisms of the loss of dehydration tolerance. In the present study, proteins that were differentially expressed between fully turgid (control), dehydrated tolerant (four-day-old) and dehydrated sensitive (six-day-old) wheat seedlings were analysed. Protein spots having at least a significant (p < 0.05) two-fold change in protein abundance were selected by Delta2D as differentially expressed, identified by MALDI-TOF and LC-MS/MS, and classified according to their function. The observed changes in the proteomic patterns of the differentially S-nitrosylated and S-glutathionylated proteins were highly specific in dehydration-tolerant and -sensitive wheat seedlings. The metabolic function of these proteins indicates that dehydration tolerance is mainly related to nucleic acids, protein metabolism, and energy metabolism. It has been proven that leaf-specific thionins BTH6 and DB4, chloroplastic 50S ribosomal protein L16, phospholipase A1-II delta, and chloroplastic thioredoxin M2 are both S-nitrosylated and S-glutathionylated upon water deficiency. Our results revealed the existence of interplay between S-nitrosylation and S-glutathionylation, two redox-regulated protein posttranslational modifications that could enhance plant defence mechanisms and/or facilitate the acclimation of plants to unfavourable environmental conditions.

Effect of Acetyl-L-Carnitine on Antioxidant Status, Lipid Peroxidation, and Oxidative Damage of Arsenic in Rat

Arsenic (As) is a widespread environmental contaminant present around the world in both organic and inorganic forms. Oxidative stress is postulated as the main mechanism for As-induced toxicity. This study was planned to examine the protective effect of acetyl-L-carnitine (ALC) on As-induced oxidative damage in male rats. Animals were randomly divided into four groups of control (saline), sodium arsenite (NaAsO2, 20 mg/kg), ALC (300 mg/kg), and NaAsO2 plus ALC. Animals were dosed orally for 28 successive days. Blood and tissue samples including kidney, brain, liver, heart, and lung were collected on the 28th day and evaluated for oxidative damage and histological changes. NaAsO2 exposure caused a significant lipid peroxidation as evidenced by elevation in thiobarbituric acid-reactive substances (TBARS). The activity of antioxidant enzymes such as glutathione-S-transferase (GST), catalase (CAT), superoxide dismutase (SOD), as well as sulfhydryl group content (SH group) was significantly suppressed in various organs following NaAsO2 treatment (P < 0.05). Furthermore, NaAsO2 administration increased serum values of alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), and bilirubin. Our findings revealed that co-administration of ALC and NaAsO2 significantly suppressed the oxidative damage induced by NaAsO2. Tissue histological studies have confirmed the biochemical findings and provided evidence for the beneficial role of ALC. The results concluded that ALC attenuated NaAsO2-induced toxicity, and this protective effect may result from the ability of ALC in maintaining oxidant-antioxidant balance.

β-Substituting alanine synthases: roles in cysteine metabolism and abiotic and biotic stress signalling in plants

Cysteine is required for the synthesis of proteins and metabolites, and is therefore an indispensable compound for growth and development. The β-substituting alanine synthase (BSAS) gene family encodes enzymes known as O-acetylserine thiol lyases (OASTLs), which carry out cysteine biosynthesis in plants. The functions of the BSAS isoforms have been reported to be crucial in assimilation of S and cysteine biosynthesis, and homeostasis in plants. In this review we explore the functional variation in this classic pyridoxal-phosphate-dependent enzyme family of BSAS isoforms. We discuss how specialisation and divergence in BSAS catalytic activities makes a more dynamic set of biological routers that integrate cysteine metabolism and abiotic and biotic stress signalling in Arabidopsis thaliana (L.) Heynh. and also other species. Our review presents a universal scenario in which enzymes modulating cysteine metabolism promote survival and fitness of the species by counteracting internal and external stress factors.