Ascorbate and glutathione: the heart of the redox hub

Hydrogen sulfide mechanism of action in plants; from interaction with regulatory molecules to persulfidation of proteins

Hydrogen sulfide (H2S), previously known as a toxic gas, is currently considered one of the most important gaseous transmitters in plants. This novel signaling molecule has been determined to play notable roles in plant growth, development, and maturation. In addition, pharmacological and genetic evidence indicated that this regulatory molecule effectively ameliorates various plant stress conditions. H2S is involved in these processes by changing gene expression, enzyme activities, and metabolite concentrations. During its regulatory function, H2S interacts with other signaling pathways such as hydrogen peroxide (H2O2), nitric oxide (NO), Ca2+, carbon monoxide (CO), phosphatidic acid (PA), phytohormones, etc. The H2S mechanism of action may depend on the persulfidation post-translational modification (PTM), which attacks the cysteine (Cys) residues on the target proteins and changes their structure and activities. This review summarized H2S biosynthesis pathways, its role in sulfide state, and its donors in plant biology. We also discuss recent progress in the research on the interactions of H2S with other signaling molecules, as well as the role of persulfidation in modulating various plant reactions.

Overexpression of E. coli formaldehyde metabolic genes pleiotropically promotes Arabidopsis thaliana growth by regulating redox homeostasis

Formaldehyde (FA) is a hazardous pollutant causing acute and chronic poisoning in humans. While plants provide a natural method of removing FA pollution, their ability to absorb and degrade FA is limited. To improve the ability of plants to degrade FA, we introduced the E. coli FrmA gene into Arabidopsis thaliana alone (FrmAOE lines) or with FrmB (FrmA/BOE lines). The transgenic seedlings had approximately 30 % longer primary roots and a 20 % higher fresh weight than the control plants. The transgenic plants started flowering four days earlier and had about 30 % more kilo-seed weight than the wild type. FrmA/BOE and FrmAOE accumulated 40 % more reactive oxidative species (ROS) in mesophyll protoplasts and leaf tissue than wild-type plants under normal conditions. In the presence of FA, they produced 92 % and 26 % more glutathione (GSH) and 6 % and 4 % more ascorbate (AsA), respectively, compared to wild-type plants and thus scavenged FA-induced ROS more effectively. The degradation efficiency of the transgenic leaf extract for FA was 73 % and 44 % higher than that of the wild type, respectively, which was also emphasized by a 2 %-26 % increase in the activity of antioxidant enzymes such as SOD and APx. By revealing the functional divergence between microbial and plant FA metabolic pathways, our work has not only highlighted the promising pluripotency of microbial genes in promoting normal plant growth and detoxifying organic pollutants simultaneously, but also revealed another layer of complexity of plant defense mechanisms against organic toxins related to ROS scavenging.

Nitrogen Assimilation Plays a Role in Balancing the Chloroplastic Glutathione Redox Potential Under High Light Conditions

Nitrate reduction requires reducing equivalents produced by the photosynthetic electron transport chain. Therefore, it has been suggested that nitrate assimilation provides a sink for electrons under high light conditions. We tested this hypothesis by monitoring photosynthetic efficiency and the chloroplastic glutathione redox potential (chl-EGSH) of plant lines with mutated glutamine synthetase 2 (GS2) and ferredoxin-dependent glutamate synthase 1 (GOGAT1). Mutant lines incorporated significantly less isotopically-labelled nitrate into amino acids than wild-type plants, demonstrating impaired nitrogen assimilation. When nitrate assimilation was compromised, photosystem II (PSII) proved more vulnerable to photodamage. The effect of the nitrate assimilation pathway on the chl- EGSH was monitored using the chloroplast-targeted roGFP2 biosensor (chl-roGFP2). Remarkably, while oxidation followed by reduction of chl-roGFP2 was detected in WT plants in response to high light, oxidation values were stable in the mutant lines, suggesting that chl-EGSH relaxation after high light-induced oxidation is achieved by diverting excess electrons to the nitrogen assimilation pathway. Importantly, similar ΦPSII and chl-roGFP2 patterns were observed at elevated CO2, suggesting that mutant phenotypes are not associated with photorespiration activity. Together, these findings indicate that the nitrogen assimilation pathway serves as a sustainable energy dissipation route, ensuring efficient photosynthetic activity and fine-tuning redox metabolism under light-saturated conditions.

The Vacuolar Inositol Transporter BvINT1;1 Contributes to Raffinose Biosynthesis and Reactive Oxygen Species Scavenging During Cold Stress in Sugar Beet

Despite a high sucrose accumulation in its taproot vacuoles, sugar beet (Beta vulgaris subsp. vulgaris) is sensitive to freezing. Earlier, a taproot-specific accumulation of raffinose was shown to have beneficial effects on the freezing tolerance of the plant. However, synthesis of raffinose and other oligosaccharides of the raffinose family depends on the availability of myo-inositol. Since inositol and inositol-metabolising enzymes reside in different organelles, functional inositol metabolism and raffinose synthesis depend on inositol transporters. We identified five homologues of putative inositol transporters in the sugar beet genome, two of which, BvINT1;1 and BvINT1;2, are localised at the tonoplast. Among these, only the transcript of BvINT1;1 is highly upregulated in sugar beet taproots under cold. BvINT1;1 exhibits a high transport specificity for inositol and sugar beet mutants lacking functional BvINT1;1 contain increased inositol levels, likely accumulating in the vacuole, and decreased raffinose contents under cold treatment. Due to the quenching capacity of raffinose for Reactive Oxygen Species (ROS), which accumulate under cold stress, bvint1;1 sugar beet plants show increased expression of both, ROS marker genes and detoxifying enzymes. Based on these findings, we conclude that the vacuolar inositol transporter BvINT1;1 is contributing to ROS-homoeostasis in the cold metabolism of sugar beet.

The overexpression of E. coli formaldehyde metabolism genes in Arabidopsis conferred varying degrees of resistance to oxidative stress induced by small organic compounds

Small organic compounds (SOCs) are widespread environmental pollutants that pose a significant threat to ecosystem health and human well-being. In this study, the FrmA gene from Escherichia coli was overexpressed alone or in combination with FrmB in Arabidopsis thaliana and their resistance to multiple SOCs was investigated. The transgenic plants exhibited varying degrees of increased tolerance to methanol, formic acid, toluene, and phenol, extending beyond the known role of FrmA in formaldehyde metabolism. Biochemical and histochemical analyses showed reduced oxidative damage, especially in the FrmA/BOE lines, as evidenced by lower malondialdehyde (MDA), H2O2 and O2•- levels, indicating improved scavenging of reactive oxygen species (ROS). SOC treatment led to significantly higher levels of glutathione (GSH) and, to a lesser extent, ascorbic acid (AsA) in the transgenic plants than in the wild-types. After methanol exposure, GSH levels increased by 95 % and 72 % in the FrmA/BOE and FrmAOE plants, respectively, while showing no significant increase in the wild-type plants. The transgenic plants also maintained higher GSH:GSSG and AsA:DHA ratios, exhibited upregulated glutathione reductase (GR) and dehydroascorbate reductase (DHAR) activities, and correspondingly increased gene expression. In addition, the photosynthetic parameters of the transgenic plants were less affected by SOC stress, which represents a significant photosynthetic advantage. These results emphasize the potential of genetically engineered plants for phytoremediation and crop improvement, as they exhibit increased tolerance to multiple hazardous SOCs. This research lays the foundation for sustainable approaches to combat pollution and improve plant resilience in the face of escalating environmental problems.

Bacillus vallismortis acts against ginseng root rot by modifying the composition and microecological functions of ginseng root endophytes

Introduction

The endophytic microbiome serves a crucial function as a secondary line of defense against pathogen invasion in plants. This study aimed to clarify the mechanism of action of the ginseng plant growth-promoting rhizobacteria (PGPR) Bacillus vallismortis SZ-4 synergizing with endophytic microorganisms in the prevention and control of root rot.

Methods

Ginseng root samples from a susceptible group (CK) with a disease level of 0-2 and a biocontrol group (BIO) treated with strain SZ-4 were collected. We employed high-throughput sequencing to examine the microbial community structure of ginseng roots at different disease levels, explore beneficial endophytic bacteria, and evaluate the efficacy of strain SZ-4 in mitigating root rot through synergistic interactions with ginseng endophytic flora.

Results

The application of the PGPR B. vallismortis SZ-4 biocontrol fungicide has been found to help ginseng resist Fusarium solani by modulating the richness and structure of endophytic microbial populations. The endophytic bacteria HY-43 and HY-46 isolated from ginseng roots treated with B. vallismortis SZ-4 were identified as Bacillus velezensis based on morphological, physiological, and biochemical characteristics, as well as 16S rDNA and gyrB sequencing analyses. The endophytic bacteria HY-43 and HY-46 were combined with strain SZ-4 to generate the bacterial consortia CS4-43 and CS4-46, respectively. Both CS4-43 and CS4-46 significantly enhanced the inhibitory effects of the single strain SZ-4, as well as HY-43 and HY-46, against ginseng root rot, while also promoting plant growth.

Discussion

These findings offers a theoretical foundation for studying the microecological prevention and control of ginseng diseases as well as new insights for conducting research on the efficient and precise management of plant diseases.

Integrated transcriptomics and metabolomics to explore the mechanisms of Elaeagnus mollis diels seed viability decline

Elaeagnus mollis Diels, is a rare and endangered woody plant endemic to China, which is listed on the IUCN Red List. In the natural state, the viability of its seeds declines very rapidly, which is the key to its endangered status, but the mechanism of E. mollis seed viability decline is still unclear. In order to explore the physiological and molecular mechanism of viability decline of E. mollis seeds, this study used fresh seeds as a control to compare and analyze the changes of seed vitality, antioxidant system, transcription and metabolomics, when seeds were stored for 1 and 3 months at room temperature. The viability of E. mollis seed decreased continuously after 1 month and 3 months of storage. The activities of superoxide dismutase (SOD), monodehydroascorbate reductase (MDHAR), ascorbate (AsA), and glutathione (GSH) decreased significantly, while catalase (CAT) activity increased gradually during the decline of seed viability. Transcriptomic results showed that a total of 801 differentially expressed genes (DEGs) were identified between fresh and 1-month-stored seeds, while 1,524 were identified between fresh and 3-month-stored seeds. Among them, the expression of CAT, MDHAR, GSH and GR were consistent with the results of physiological indicators. Moreover, WRKY, C3H, bZIP, B3, bHLH, NAC and AP2 / ERF-ERF transcription factors are important in regulating seed viability. Metabolomics results showed that the types of differential accumulated metabolites (DAMs) during viability decline were mainly flavonoids, amino acids and derivatives, and phenolic acids. The combined analysis results of transcriptomics and metabolomics further showed that DEGs and DAMs associated with viability were co-enriched in flavonoid biosynthesis and tryptophan metabolism pathways. Also identified were 22 key antioxidant genes, including CAT, ALDH, CHS and C4H, which were identified as participating in the changes of seed viability. This also illustrated that the metabolic pathways of flavonoid biosynthesis and tryptophan metabolism were involved in regulating the decline of seed viability by acting on the antioxidant system. These findings provide new insights into the mechanism of seed viability decline of E. mollis.

Cyanobacteria-Pesticide Interactions and Their Implications for Sustainable Rice Agroecosystems

Modern agricultural practices rely heavily on fertilizers and pesticides to boost crop yields, essential for feeding the growing global population. However, their extensive use poses significant environmental risks. Chemical-based fertilizers and pesticides persist in ecosystems, potentially harming ecological stability. Wetland rice farming utilizing nitrogen-fixing cyanobacteria has emerged as an ecofriendly alternative, drawing attention due to its capacity to mitigate pesticide-related issues. Cyanobacteria, capable of fixing atmospheric nitrogen, thrive in low-nitrogen conditions and can aid plant growth. Some species can also biodegrade pesticides, offering a means to clean up contaminated environments. Researchers are exploring ways to leverage cyanobacteria's nitrogen fixation and biodegradation abilities for ecofriendly biofertilizers and environmental cleanup. This approach presents promise for sustainable agriculture and environmental preservation. The current study delves into multiple studies to investigate global pesticide usage levels, primary categorization, and persistence patterns. It also investigates cyanobacterial distribution and their interactions with pesticides in wetland rice ecosystems, aiming to enable their use in sustainable agriculture. Additionally, the review provides a thorough summary of the literature's findings about the potential of cyanobacteria in pesticide degradation.

Jasmonic acid signaling and glutathione coordinate plant recovery from high light stress

High light (HL)-induced chloroplast retrograde signaling originates from the photosynthetic apparatus and regulates nuclear gene expression to enhance photoprotection and coordination of cell metabolism. Here, we analyzed the transcript profiles and accumulation of ROS, stress hormones, and small molecule antioxidants to investigate the signaling mechanisms operating under HL stress, particularly during plant recovery under growth light condition. Exposure of Arabidopsis (Arabidopsis thaliana) rosettes to HL for 15 min induced several 1O2- and H2O2-responsive genes and accumulation of an oxidized form of glutathione, the hallmarks of oxidative stress in cells. Prolonged exposure to HL resulted in accumulation of transcripts encoding oxylipin biosynthesis enzymes, leading to accumulation of 12-oxo-phytodienoic acid and jasmonic acid. However, the expression of several jasmonic acid-responsive genes, already induced by HL, peaked during the recovery, together with accumulation of jasmonic acid and reduced glutathione and ascorbate, highlighting the critical role of jasmonic acid signaling in restoring chloroplast redox balance following HL stress. The involvement of jasmonic acid signaling in recovery-sustained gene expression was further confirmed via experiments with jasmonic acid receptor mutants. HL exposure of only 2 min was sufficient to induce some recovery-sustained genes, indicating the rapid response of plants to changing light conditions. We propose that ROS production at HL induces the signaling cascade for early oxylipin biosynthesis and 12-oxo-phytodienoic acid accumulation, while increased accumulation of jasmonic acid in the recovery phase activates genes that fully restore the glutathione metabolism, ultimately allowing recovery from short-term HL stress.

Sex-specific ozone stress responses of poplar: Mechanisms of enhanced tolerance of males

Uncovering whether the ozone (O3)-sensitivity differs between sexes in Populus deltoides and if so, what are the mechanisms underlying the different sensitivities is vital for understanding plant-adaptation-strategy in O3 polluted areas. We exposed female and male saplings to 80 nmol mol-1 O3 for 14 days, measured the growth, structural and physiological characteristics, metabolite accumulations, and gene transcription levels, to test the hypothesis that the enhanced resistance in males is associated with their traits detoxifying and reducing O3 entry into the cells. In general, females showed more severe visible injury, larger reductions in leaf biomass, chlorophyll content, and photosynthetic characteristics than males. The emission of isoprene and its synthase gene expression were inhibited by O3 in both sexes with less reductions in males than females. The up-regulated differentially expressed genes in males under O3 stress were mainly enriched in phenylpropanoid biosynthesis and glutathione metabolism pathways, while in females they were primarily enriched in the flavonoid biosynthesis pathway. Accordingly, males accumulated more lignin, lignans, and coumarins, while females accumulated more flavonoids. Overall, the stronger tolerance to O3 in males than females was possibly related to their combined up-regulation of multiple defense pathways that reduce both the oxidative stress and O3 permeability into cytosol.

Peptides and Reactive Oxygen Species Regulate Root Development

Like phytohormones, peptide hormones participate in many cellular processes, participate in intercellular communications, and are involved in signal transmission. The system of intercellular communications based on peptide-receptor interactions plays a critical role in the development and functioning of plants. One of the most important molecules are reactive oxygen species (ROS). ROS participate in signaling processes and intercellular communications, including the development of the root system. ROS are recognized as active regulators of cell division and differentiation, which depend on the oxidation-reduction balance. The stem cell niche and the size of the root meristem are maintained by the intercellular interactions and signaling networks of peptide hormone and ROS. Therefore, peptides and ROS can interact with each other both directly and indirectly and function as regulators of cellular processes. Peptides and ROS regulate cell division and stem cell differentiation through a negative feedback mechanism. In this review, we focused on the molecular mechanisms regulating the development of the main root, lateral roots, and nodules, in which peptides and ROS participate.

Redox regulation of autophagy in Arabidopsis: The different ROS effects

Autophagy plays a key role in the responses to different stress condition in plants. Reactive oxygen species (ROS) are common modulators of stress responses, having both toxic and signaling functions. In this context, the relationship between ROS and autophagy regulation remains unclear, and in some aspects, contradictory. In this study, we employed pharmacological and genetic approaches to investigate the effects of different ROS on the cytoplastic redox state and autophagic flux in Arabidopsis thaliana. Our results demonstrated that oxidative treatments with H2O2 and MV, which drastically increased the oxidized state of the cytoplasm, reduced the autophagic flux. Conversely, singlet oxygen, which did not have significant effects on the cytoplasmic redox state, increased the autophagic flux. Additionally, our findings indicated that after H2O2 and high light treatments and during the recovery period, the cytoplasm returned to its reduced state, while autophagy was markedly induced. In summary, our study unveils the differential effects of ROS on the autophagic flux, establishing a correlation with the redox state of the cytoplasm. Moreover, it emphasizes the dynamic nature of autophagy in response to oxidative stress and the subsequent recovery period.

Exogenous γ-aminobutyric acid mitigates drought-induced impairments in Thymus daenensis Celak by regulating physiological traits, antioxidant enzymes and essential oil constituents

Drought stress is one of the most significant environmental challenges, leading to various changes in the physiological processes of plants. Gamma-aminobutyric acid (GABA) is an essential biomolecule that plays a critical role in regulating growth and stress signaling. The current study aims to investigate the effects of GABA on antioxidant enzyme activity and the essential oil composition of Thymus daenensis Celak under different levels of water deficit stress. We examined three different levels of soil moisture (90%, 60%, and 30% of field capacity) alongside three GABA foliar treatments (0 mM, 25 mM, 50 mM, and 75 mM). The results showed that applying 25 mM GABA under severe stress conditions (at 30% of field capacity) significantly increased the activity levels of ascorbate peroxidase, guaiacol peroxidase, and superoxide dismutase enzymes by 95.5%, 78.45%, and 38%, respectively. Additionally, applying GABA at various levels during different water stress treatments led to significant improvements in the chlorophyll, carotenoid, and proline content in leaf tissues. Specifically, the application of 25, 50, and 75 mM GABA enhanced the proline content in T. daenensis by 53.9%, 26.8%, and 11%, respectively, compared to the control group (non-application of GABA). Essential oil analysis revealed the following ranges: thymol was present in the range of 38.07-45.18%, cymene in the range of 5.13-14.10%, caryophyllene in the range of 4.3-23.01%, and cineole in the range of 2-4.15%. The highest amount of thymol was obtained in the absence of GABA at 30% field capacity, while the greatest amount of cymene was also observed without GABA at 90% field capacity. Additionally, the maximum concentration of caryophyllene was found when 50 mM GABA was applied at 90% field capacity, and the maximum level of cineole was detected with 75 mM GABA at 90% field capacity. In conclusion, the exogenous application of GABA demonstrated favorable efficacy, particularly at a concentration of 25 mM. This treatment resulted in a significant enhancement of the plant's defense mechanisms and created favorable conditions that notably impacted the quality of the essential oil produced by T. daenensis.

Genome-wide association studies and transcriptomics reveal mechanisms explaining the diversity of wheat root responses to nutrient availability

Nutrient availability profoundly influences plant root system architecture, which critically determines crop productivity. While Arabidopsis has provided important insights into the genetic responses to nutrient deficiency, translating this knowledge to crops, particularly wheat, remains a subject of inquiry. Here, examining a diverse wheat population under varying nitrogen (N), phosphorus (P), potassium (K), and iron (Fe) levels, we uncover a spectrum of root responses, spanning from growth inhibition to stimulation, highlighting genotype-specific strategies. Furthermore, we reveal a nuanced interplay between macronutrient deficiency (N, P, and K) and Fe availability, emphasizing the central role of Fe in modulating root architecture. Through genome-wide association mapping, we identify 11 quantitative trait loci underlying root traits under varying nutrient availabilities, including homologous genes previously validated in Arabidopsis, supporting our findings. In addition, utilizing transcriptomics, reactive oxygen species (ROS) imaging, and antioxidant treatment, we uncover that wheat root growth inhibition by nutrient deficiency is attributed to ROS accumulation, akin to the role of ROS in governing Arabidopsis root responses to nutrient deficiency. Therefore, our study reveals the conservation of molecular and physiological mechanisms between Arabidopsis and wheat to adjust root growth to nutrient availability, paving the way for targeted crop improvement strategies aimed at increasing nutrient use efficiency.

Seed priming with NaCl boosted the glutathione-ascorbate pool to facilitate photosystem-II function and maintain starch in NaCl-primed chickpea under salt stress

Seed priming with NaCl improved the tissue tolerance nature in moderately salt-tolerant cultivar Anuradha under salt stress. Is an improved tissue tolerance in primed chickpea seedlings supplemented with a boosted antioxidant response? To investigate, a seed priming experiment with sub-lethal salt concentration (50 mM NaCl) was performed with chickpea cv. Anuradha. The morphological, physiological, biochemical, and molecular responses associated with reactive oxygen species, antioxidant activities, photosystem-II (PS-II) efficiency, and starch-sugar metabolism were studied at 150 mM NaCl in hydroponically grown nonprimed and primed seedlings. Primed chickpea seedlings maintained high biomass compared to nonprimed seedlings under stress. High level of reduced ascorbate, glutathione contents and higher activity of glutathione reductase and dehydroascorbate reductase suggested that primed seedling improved the antioxidant response, thus able to maintain low hydrogen peroxide under stress. High photosystem-II (PS-II) efficiency and high electron transport rate of PS-II in primed chickpea seedlings under stress suggested that primed seedlings are able to maintain PS-II function under stress, thus able to retain the flow of electrons for PS-II. A high starch content and low alpha amylase gene expression in primed seedlings suggested that NaCl priming could utilize the reserve food compounds slowly. Overall, this study uncovers that seed priming with NaCl boosted the antioxidant responses in primed chickpea seedlings to stabilize the PS-II function and facilitates the flow of electrons for PS-II, indispensable for energy generation, thus reducing the need of starch degradation and maintaining better starch-sugar equilibrium in primed seedlings.

DNA Damaging Agents Induce RNA Structural and Transcriptional Changes for Genes Associated with Redox Homeostasis in Arabidopsis thaliana

Living organisms are constantly exposed to various DNA damaging agents. While the mechanisms of DNA damage and DNA repair are well understood, the impact of these agents on RNA secondary structure and subsequent function remains elusive. In this study, we explore the effects of DNA damaging reagent methyl methanesulfonate (MMS) on arabidopsis gene expression and RNA secondary structure using the dimethyl sulfate (DMS) mutational profiling with sequencing (DMS-MaPseq) method. Our analyses reveal that changes in transcriptional levels and mRNA structure are key factors in response to DNA damaging agents. MMS treatment leads to the up-regulation of arabidopsis RBOHs (respiratory burst oxidase homologues) and alteration in the RNA secondary structure of GSTF9 and GSTF10, thereby enhancing mRNA translation efficiency. Redox homeostasis manipulated by RBOHs and GSTFs plays a crucial role in MMS-induced primary root growth inhibition. In conclusion, our findings shed light on the effects of DNA damaging agents on RNA structure and potential mRNA translation, which provide a new insight to understand the mechanism of DNA damage.

Application of the composite nanoparticles of selenium and chitosan for ameliorating arsenic stress in rice seedlings

Selenium nanoparticles are well known for their antioxidant and stress-mitigating properties. In our study, composite nanoformulations of selenium and chitosan have been synthesized. The synthesized composite nanoformulations were 50 nm in diameter, spherical in shape, and had higher antioxidant activities and stability than the selenium and chitosan nanoparticles. In our study, Luit rice seedlings grown in an arsenic-treated Hoagland solution showed a reduction of growth, decreased superoxide dismutase, catalase, ascorbate peroxidase, guaiacol peroxidase, ascorbate, and glutathione content. Otherwise, superoxide anion, hydrogen peroxide, and malondialdehyde content increased in arsenic-stressed conditions. The alone application of Selenium nanoparticles, chitosan nanoparticles, and their nanoformulation improved growth, reduced stress parameters, and enhanced enzymatic and non-enzymatic activity. Additionally, the reduction of superoxide anion, hydrogen peroxide, and malondialdehyde content was higher by applying composite nanoformulations in arsenic-stressed conditions than selenium and chitosan nanoparticles. The treatment of composite nanoformulation also regulated the enzymatic and non-enzymatic antioxidant activity higher than that of other nanoparticles. It might be due to the higher stability and antioxidant activity of composite nanoformulations than that of selenium and chitosan nanoparticles. Our study suggests that the composite nanoformulation enhanced the growth of rice plants by mitigating arsenic-induced reactive oxygen species and upregulating antioxidant activity.

Multi-Omics Analysis Reveals That AhNHL Contributes to Melatonin-Mediated Cadmium Tolerance in Peanut Plants

Cadmium (Cd) pollution significantly hampers cleaner production of peanut (Arachis hypogaea L.). Therefore, exploring of tolerance mechanisms to Cd stress and breeding of low-Cd peanut cultivars are urgently needed and require intense efforts. Herein, multi-omics and physiological studies reveal that multiple biological processes, including melatonin (MT) biosynthesis, are involved in the Cd tolerance in peanut plants. Exogenous MT was applied to peanut plants under Cd stress, which decreased Cd accumulation in roots, shoots and seeds for 40%-60%, and promoted the antioxidant capacity. Integrated investigation reveals that MT-mediated Cd tolerance is mainly attributed to the enhanced metabolism of linolenic acid, glutathione (GSH), and phenylpropanoid (lignin), and development of casparian strip in root cell wall. Defense genes, such as non-race-specific disease resistance gene 1/harpininduced gene 1 (NDR1/HIN1)-like in peanut (AhNHL), were also significantly upregulated by MT under Cd stress. Overexpression of the AhNHL gene in tobacco reduced Cd accumulation for 37%-46%, and alleviated photosynthesis-inhibition induced by Cd stress. Transcriptomic analysis suggested that AhNHL confers the Cd tolerance mainly through promoting phenylpropanoid biosynthesis and GSH metabolism. Additionally, exogenous GSH effectively alleviated the Cd stress through improving Cd sequestration and antioxidant capacity in peanut plants, while apply of the GSH biosynthesis inhibitor (buthionine sulfoximine) exacerbated the Cd phytotoxicity. Transcriptomic analysis reveals that exogenous GSH improves Cd tolerance through affecting the expression of genes involved in transcription regulation, and metal ion binding and transport. Our findings provide novel insights into molecular mechanisms underlying Cd tolerance in plants, which would facilitate breeding of low-Cd peanut cultivars.

Physiological effects of sulfadiazine and sulfamethoxazole on Skeletonema costatum and toxicological evaluation using IBRv2 index

Sulfonamide antibiotics, widely used in human and veterinary medicine as well as agriculture, pose environmental concerns due to their stability and poor biodegradability. This study fills a critical gap in understanding the ecological impact of sulfonamide antibiotics on marine microalgae, particularly Skeletonema costatum, a key primary producer in marine ecosystems. This study investigated the biological responses of the marine microalga Skeletonema costatum to sulfadiazine (SD) and sulfamethoxazole (SMX). Both antibiotics significantly impacted S. costatum, with SD having a more pronounced effect. Growth studies showed a clear dose-response relationship: Low concentrations (0.5 mg/L) of SD and SMX stimulated growth, while higher concentrations (3 mg/L, 5 mg/L, and 10 mg/L) inhibited growth. The 96-hour half-maximal inhibitory concentrations (96h-IC50) were 1.654 mg/L and 1.838 mg/L, respectively, initially indicating that SD has a stronger inhibitory effect on S. costatum than SMX. Photosynthetic activity, measured by chlorophyll a content and the maximum quantum yield of photosystem II (Fv/Fm) values, showed that low concentrations (0.5 mg/L) of SD and SMX increased photosynthetic efficiency, while high concentrations (3 mg/L, 5 mg/L, and 10 mg/L) significantly inhibited it. Antioxidants activity analysis revealed that SD and SMX exposure altered superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), glutathione reductase (GR), and malondialdehyde (MDA) levels. SOD, GR, and GSH-Px levels initially increased but later decreased, suggesting a synergistic effect, while MDA levels consistently increased, indicating oxidative stress and biochemical disruption in algal cells. The Integrated Biomarker Response Version 2 (IBRv2) index provided a comprehensive evaluation of the ecological risks posed by SD and SMX, demonstrating that these antibiotics can significantly disrupt the physiology of marine microalgae. The IBRv2 index provided a comprehensive evaluation of the ecological risks posed by SD and SMX, demonstrating that these antibiotics can significantly disrupt the physiology of marine microalgae. Higher IBRv2 values for SD exposure indicated more substantial impacts on S. costatum. This study underscores the significant ecological risks of sulfonamide antibiotics in marine environments, highlighting the need for further research and regulation to mitigate their impact.

Progress in Plant Nitric Oxide Studies: Implications for Phytopathology and Plant Protection

Nitric oxide (NO) is a gaseous free radical known to modulate plant metabolism through crosstalk with phytohormones (especially ABA, SA, JA, and ethylene) and other signaling molecules (ROS, H2S, melatonin), and to regulate gene expression (by influencing DNA methylation and histone acetylation) as well as protein function through post-translational modifications (cysteine S-nitrosation, metal nitrosation, tyrosine nitration, nitroalkylation). Recently, NO has gained attention as a molecule promoting crop resistance to stress conditions. Herein, we review innovations from the NO field and nanotechnology on an up-to-date phytopathological background.

Glycine betaine enhances tolerance of low temperature combined with low light in pepper (Capsicum annuum L.) by improving the antioxidant capacity and regulating GB metabolism

Glycine betaine (GB) is commonly used as an osmotic regulator and a donor to facilitate changes in methylation in plants and animals, thereby enhancing stress resistance. However, low temperature combined with low light stress represent the most prevalent stresses during pepper growth period in northwest China, and limited studies have focused on the potential stress-mitigating effects of GB. Therefore, to examine the regulatory mechanism of GB-induced tolerance to LL stress, pepper seedlings were pretreated with 20 mmol L-1 GB and 60 μmol L-1 3-Deazaneplanocin A hydrochloride at a temperature of 10/5 °C and illumination of 100 μmol m-2 s-1. The results demonstrated that GB significantly alleviated the detrimental effects of low temperature combined with low light stress on growth of primary and lateral roots and increased the roots absorption of mineral nutrients (N, P, Ca, Fe, and Zn). In addition, GB induced the expression of the genes for CaSOD, CaPOD, CaCAT, CaGR1, and CaDHAR, improved osmotic regulation, and increased the activities of enzymatic (superoxide dismutase, peroxidase, catalase, glutathione reductase, and dehydroascorbate reductase) and non-enzymatic antioxidants (ascorbate and glutathione). This resulted in enhanced scavenging of reactive oxygen species, thereby maintaining a balanced oxidation-reduction within the cells. Furthermore, GB substituted S-adenosylmethionine, a partial methylation donor, during the methyl group metabolism process, altering the m6A methylation level and increasing the resistance of pepper seedlings to LL stress. Overall, exogenous GB pretreatment could be used as a potential strategy for enhancing the LL tolerance of plants.

Identification and Expression Analysis of the Soybean Serine Acetyltransferase (SAT) Gene Family Under Salt Stress

Serine acetyltransferase (SAT) is a critical enzyme in the sulfur-assimilation pathway of cysteine, playing an essential role in numerous physiological functions in plants, particularly in their response to environmental stresses. However, the structural characteristics of the soybean SAT gene family remain poorly understood. Members of the soybean SAT gene family were identified using the Hidden Markov Model approach. Bioinformatics tools, such as ExPASy, PlantCARE, MEME, and TBtools-II, were employed to examine the physicochemical properties, cis-regulatory elements, conserved motifs, gene structures, and chromosomal positions of the GmSAT genes. RT-qPCR was conducted to evaluate the expression profiles of GmSAT genes under NaCl-induced stress, identifying genes likely involved in the salt-stress response. A total of ten GmSAT genes were identified in the soybean genome and grouped into three subfamilies. Genes within each subfamily shared notable structural similarities and conserved motifs. Analysis of cis-regulatory elements revealed that the promoters of these genes contain several elements linked to plant growth and stress-related responses. Expression patterns of GmSAT genes varied across different soybean tissues, with GmSAT10 showing higher expression in roots, while GmSAT1 and GmSAT2 had lower expression in the same tissue. Following NaCl treatment, expression levels of seven GmSAT genes were significantly increased in the roots, indicating their potential involvement in the plant's adaptation to salt stress. GmSAT genes appear to play crucial roles in soybean's response to salt stress, offering insights that could aid in the development of salt-tolerant soybean varieties.

A Comparative Transcriptomic Study Reveals Temporal and Genotype-Specific Defense Responses to Botrytis cinerea in Grapevine

Grapevine (Vitis vinifera L.), a globally significant crop, is highly susceptible to Botrytis cinerea, the causative agent of gray mold disease. This study investigates transcriptomic responses to B. cinerea in tolerant and susceptible grapevine genotypes using RNA sequencing (RNA-seq). Differentially expressed genes (DEGs) were identified at three time points (T1, T2, T3), highlighting both genotype-independent and genotype-specific responses. Early-stage infection (T1) revealed rapid and robust activation of defense pathways in both genotypes, though the tolerant genotype showed enhanced modulation of metabolic processes by T2, prioritizing secondary metabolism and stress adaptation over growth. In contrast, the susceptible genotype exhibited less coordinated metabolic reprogramming, with delayed or weaker activation of key defense mechanisms. Gene Ontology and KEGG analyses identified critical pathways, including phenylpropanoid biosynthesis-like lignin metabolism, MAPK signaling, as well as candidate genes such as WRKY transcription factors and enzymes involved in cell wall fortification and antifungal compound biosynthesis. Genotype-specific responses emphasized metabolic flexibility as a determinant of resistance, with the tolerant genotype exhibiting superior resource allocation to defense pathways. These findings provide insights into the molecular basis of grapevine resistance to B. cinerea, offering potential targets for breeding or genetic engineering to enhance resilience and reduce fungicide dependency.

Vitamin C: From Self-Sufficiency to Dietary Dependence in the Framework of Its Biological Functions and Medical Implications

Vitamin C is an organic compound biosynthesized in plants and most vertebrates. Since its discovery, the benefits of vitamin C use in the cure and prevention of various pathologies have been frequently reported, including its anti-oxidant, anti-inflammatory, anticoagulant, and immune modulatory properties. Vitamin C plays an important role in collagen synthesis and subsequent scurvy prevention. It is also required in vivo as a cofactor for enzymes involved in carnitine and catecholamine norepinephrine biosynthesis, peptide amidation, and tyrosine catabolism. Moreover, as an enzymatic cofactor, vitamin C is involved in processes of gene transcription and epigenetic regulation. The absence of the synthesis of L-gulono-1,4-lactone oxidase, a key enzyme in the pathway of vitamin C synthesis, is an inborn metabolism error in some fishes and several bird and mammalian species, including humans and non-human primates; it is caused by various changes in the structure of the original GULO gene, making these affected species dependent on external sources of vitamin C. The evolutionary cause of GULO gene pseudogenization remains controversial, as either dietary supplementation or neutral selection is evoked. An evolutionary improvement in the control of redox homeostasis was also considered, as potentially toxic H2O2 is generated as a byproduct in the vitamin C biosynthesis pathway. The inactivation of the GULO gene and the subsequent reliance on dietary vitamin C may have broader implications for aging and age-related diseases, as one of the most important actions of vitamin C is as an anti-oxidant. Therefore, an important aim for medical professionals regarding human and animal health should be establishing vitamin C homeostasis in species that are unable to synthesize it themselves, preventing pathologies such as cardiovascular diseases, cognitive decline, and even cancer.

Lead accumulation and concomitant reactive oxygen species (ROS) scavenging in Robinia pseudoacacia are dependent on nitrogen nutrition

Heavy metal pollution combined with nitrogen (N) limitation is a major factor preventing revegetation of contaminated land. Woody N2-fixing legumes are a natural choice for phytoremediation. However, the physiological responses of woody legumes to lead (Pb) with low N exposure are currently unknown. In the present study, a common Robinia cultivar from Northeast China, inoculated and non-inoculated with rhizobia, was exposed to -Pb or + Pb at moderate (norN) or low N application (lowN). Our results showed that without inoculation, independent of N application, Pb taken up by the roots was allocated to the shoot and inhibited photosynthesis and biomass production. In non-inoculated Robinia, Pb-mediated oxidative stress resulted in reduced H2O2 scavenging as indicated by increased ascorbate peroxidase (APX) activity in the leaves and proline contents in the roots, independent of N application. Combined lowN∗Pb exposure significantly increased malondialdehyde (MDA) contents in roots and leaves and enhanced APX and dehydroascorbate reductase activities in leaves compared to individual Pb exposure. Rhizobia inoculation raised the abundance of nodules and promoted Pb uptake by roots. Under Pb exposure, inoculation with rhizobia reduced MDA contents, increased proline contents in leaves and roots and enhanced activity of nitrate reductase in the leaves, independent of N application. Under Pb exposure, nitrogenase activity of inoculated Robinia under low- and norN application were similar indicating that enhanced of N2-fixation at lowN was counteracted by Pb exposure. These results show that inoculation of Robinia with rhizobia can alleviate Pb toxicity at combined lowN and Pb exposure by reducing oxidative stress.

Physiological and molecular mechanisms of exogenous salicylic acid in enhancing salt tolerance in tobacco seedlings by regulating antioxidant defence system and gene expression

Introduction

Salt stress has emerged as a predominant abiotic factor that jeopardizes global crop growth and yield. The plant hormone salicylic acid (SA) has notable potential in mitigating salt toxicity, yet its mechanism in enhancing the salinity tolerance of tobacco plants is not well explored.

Methods

This study aimed to assess the potential benefits of exogenous SA application (1.0 mM) on tobacco seedlings subjected to saline soil conditions.

Results

The foliar spray of SA partially mitigated these salt-induced effects, as evidenced by a reduction of malondialdehyde content, and improvements of leaf K+/Na+ ratios, pigment biosynthesis, and electron transport efficiency under NaCl stress. Additionally, SA increased the contents of total phenolic compound and soluble protein by 16.2% and 28.7% to alleviate NaCl-induced oxidative damage. Under salt stressed conditions, the activities of antioxidant enzymes, including superoxide dismutase, ascorbate peroxidase, catalase, and peroxidase increased by 4.2%~14.4% in SA sprayed tobacco seedlings. Exogenous SA also increased ascorbate and glutathione levels and reduced their reduced forms by increasing the activities of glutathione reductase, ascorbate peroxidase, monodehydroascorbate reductase and dehydroascorbate reductase. qRT-PCR analysis revealed that the key genes regulating SA biosynthesis, carbon assimilation, the antioxidant system and the ascorbate-glutathione cycle were activated by SA under conditions of salt stress.

Discussion

Our study elucidates the physiological and molecular mechanisms of exogenous SA in enhancing plant salt tolerance and provides a practical basis for crop improvement in saline environments.

Arbuscular mycorrhizal fungi and salinity stress mitigation in plants

In recent decades, climate change has caused a decrease in rainfall, increasing sea levels, temperatures rising, and as a result, an expansion in salt marshes across the globe. An increase in water and soil salinity has led to a decline in the cultivated areas in different areas, and consequently, a substantial decrease in crop production. Therefore, it has forced scientists to find cheap, effective and environmentally friendly methods to minimize salinity's impact on crops. One of the best strategies is to use beneficial soil microbes, including arbuscular mycorrhizal fungi, in order to increase plant tolerance to salt. The findings of this review showed that salinity can severely impact the morphological, physiological, and biochemical structures of plants, lowering their productivity. Although plants have natural capabilities to deal with salinity, these capacities are limited depending on plant type, and variety, as well as salinity levels, and other environmental factors. Furthermore, result of the present review indicates that arbuscular mycorrhizal fungi have a significant effect on increasing plant resistance in saline soils by improving the soil structure, as well as stimulating various plant factors including photosynthesis, antioxidant defense system, secondary metabolites, absorption of water and nutrients.

The role of signaling systems of plant in responding to key astrophysical factors: increased ionizing radiation, near-null magnetic field and microgravity

Plants will form the basis of artificial ecosystems in space exploration and the creation of bases on other planets. Astrophysical factors, such as ionizing radiation (IR), magnetic fields (MF) and gravity, can significantly affect the growth and development of plants beyond Earth. However, to date, the ways in which these factors influence plants remain largely unexplored. The review shows that, despite the lack of specialized receptors, plants are able to perceive changes in astrophysical factors. Potential mechanisms for perceiving changes in IR, MF and gravity levels are considered. The main pathway for inducing effects in plants is caused by primary physicochemical reactions and change in the levels of secondary messengers, including ROS and Ca2+. The presence of common components, including secondary messengers, in the chain of responses to astrophysical factors determines the complex nature of the response under their combined action. The analysis performed and the proposed hypothesis will help in planning space missions, as well as identifying the most important areas of research in space biology.

In defence of ferroptosis

Rampant phospholipid peroxidation initiated by iron causes ferroptosis unless this is restrained by cellular defences. Ferroptosis is increasingly implicated in a host of diseases, and unlike other cell death programs the physiological initiation of ferroptosis is conceived to occur not by an endogenous executioner, but by the withdrawal of cellular guardians that otherwise constantly oppose ferroptosis induction. Here, we profile key ferroptotic defence strategies including iron regulation, phospholipid modulation and enzymes and metabolite systems: glutathione reductase (GR), Ferroptosis suppressor protein 1 (FSP1), NAD(P)H Quinone Dehydrogenase 1 (NQO1), Dihydrofolate reductase (DHFR), retinal reductases and retinal dehydrogenases (RDH) and thioredoxin reductases (TR). A common thread uniting all key enzymes and metabolites that combat lipid peroxidation during ferroptosis is a dependence on a key cellular reductant, nicotinamide adenine dinucleotide phosphate (NADPH). We will outline how cells control central carbon metabolism to produce NADPH and necessary precursors to defend against ferroptosis. Subsequently we will discuss evidence for ferroptosis and NADPH dysregulation in different disease contexts including glucose-6-phosphate dehydrogenase deficiency, cancer and neurodegeneration. Finally, we discuss several anti-ferroptosis therapeutic strategies spanning the use of radical trapping agents, iron modulation and glutathione dependent redox support and highlight the current landscape of clinical trials focusing on ferroptosis.

Modulatory responses of physiological and biochemical status are related to drought tolerance levels in peanut cultivars

Peanut (Arachis hypogaea L.) is the fourth most cultivated oilseed in the world, but its cultivation is subject to fluctuations in water demand. Current studies of tolerance between cultivars and physiological mechanisms involved in plant recovery after drought are insufficient for selection of tolerant cultivars. We evaluated tolerance of different peanut cultivars to water deficit and subsequent rehydration, based on physiological and biochemical status. Gas exchange, photosynthetic pigments, Fv/Fm, MDA, H2O2 and antioxidant enzyme activity were analysed. Drought stress and rehydration triggered distinct changes in pigments, Fv/Fm, gas exchange, and H2O2 across genotypes, with increased MDA in all cultivars under stress. Based on multivariate analysis, 'IAC Sempre Verde' was identified as most drought sensitive, while 'IAC OL3', 'IAC 503', and 'IAC OL6' exhibited variations in physiological responses and antioxidant activity correlated to their respective tolerance levels. Notably, 'IAC OL3' had higher WUE and enhanced enzymatic defence and was classified as the most drought tolerant in this context. The above findings suggest that antioxidant metabolism is a important factor for plant recovery post-rehydration. Our study provides insights into antioxidant and physiological responses of peanut cultivars, which can support breeding programs for selection of drought-tolerant genotypes. Future field studies should be conducted for a better understanding of tolerance of these cultivars, particularly through correlation of these data with crop yield impact.

Preharvest methyl jasmonate application delays cell wall degradation and upregulates phenolic metabolism and antioxidant activities in cold stored raspberries

The effects of preharvest methyl jasmonate (MeJA) spray application on the physicochemical quality, metabolism of phenolics, and cell wall components in raspberries were investigated during a 10-day cold storage period. MeJA spray reduced firmness loss, decay incidence, and weight loss, while maintained higher levels of soluble solids content, ascorbic acid, anthocyanins and flavonoids in raspberries. Furthermore, MeJA application resulted in increased total pectin and protopectin levels, as well as lowered water-soluble pectin, and activities of pectin methyl esterase, polygalacturonase and cellulase enzymes. Additionally, MeJA treatment upregulated the phenylpropanoid pathway, leading to higher endogenous phenolics and activities of phenylalanine-ammonia lyase and shikimate dehydrogenase. In conclusion, preharvest MeJA spray application could be adopted to enhance the storage potential of cold-stored raspberries for 10 days by maintaining higher firmness, assuring better physicochemical quality, and increasing phenolic metabolism, while reducing cell wall hydrolysis.

AtMYB72 aggravates photosynthetic inhibition and oxidative damage in Arabidopsis thaliana leaves caused by salt stress

MYB transcription factor is one of the largest families in plants. There are more and more studies on plants responding to abiotic stress through MYB transcription factors, but the mechanism of some family members responding to salt stress is unclear. In this study, physiological and transcriptome techniques were used to analyze the effects of the R2R3-MYB transcription factor AtMYB72 on the growth and development, physiological function, and key gene response of Arabidopsis thaliana. Phenotypic observation showed that the damage of overexpression strain was more serious than that of Col-0 after salt treatment, while the mutant strain showed less salt injury symptoms. Under salt stress, the decrease of chlorophyll content, the degree of photoinhibition of photosystem II (PSII) and photosystem I (PSI) and the degree of oxidative damage of overexpressed lines were significantly higher than those of Col-0. Transcriptome data showed that the number of differentially expressed genes (DEGs) induced by salt stress in overexpressed lines was significantly higher than that in Col-0. GO enrichment analysis showed that the response of AtMYB72 to salt stress was mainly by affecting gene expression in cell wall ectoplast, photosystem I and photosystem II, and other biological processes related to photosynthesis. Compared with Col-0, the overexpression of AtMYB72 under salt stress further inhibited the synthesis of chlorophyll a (Chla) and down-regulated most of the genes related to photosynthesis, which made the photosynthetic system more sensitive to salt stress. AtMYB72 also caused the outbreak of reactive oxygen species and the accumulation of malondialdehyde under salt stress, which decreased the activity and gene expression of key enzymes in SOD, POD, and AsA-GSH cycle, thus destroying the ability of antioxidant system to maintain redox balance. AtMYB72 negatively regulates the accumulation of osmotic regulatory substances such as soluble sugar (SS) and soluble protein (SP) in A. thaliana leaves under salt stress, which enhances the sensitivity of Arabidopsis leaves to salt. To sum up, MYB72 negatively regulates the salt tolerance of A. thaliana by destroying the light energy capture, electron transport, and antioxidant capacity of Arabidopsis.

Glutathione Involvement in Potato Response to French Marigold Volatile Organic Compounds

To elucidate the involvement of glutathione in the mitigation of induced oxidative changes and the sequestration of perceived volatiles in cells, we exposed potato plants to French marigold essential oil. The formation of short-lived radicals, the determination of scavenging activity towards ascorbyl and DPPH radicals, and the assessment of the potato plants' overall intra/extracellular reduction status were performed using electron paramagnetic resonance spectroscopy (EPR). The results showed the presence of hydroxyl radicals in potatoes, with significantly reduced accumulation in exposed plants compared to the control group after 8 h. However, the kinetics of EPR signal intensity change for the pyrrolidine spin probe (3CP) in these plants showed very low reducing potential, suggesting that the antioxidant system acts lethargically and/or the probe has been reoxidized. Total glutathione and its reduced/oxidized form ratio, determined spectrophotometrically, showed that the exposed plants initially had lower glutathione levels with diminutive, reduced form compared to the control. Still, after 8 h, both characteristics were similar to those of the control. RT-qPCR analysis revealed that the volatiles altered the expression of glutathione metabolism-involved genes, especially that of glutathione-S-transferase, after 8 h. Glutathione metabolism was affected by volatiles in the initial response of potato plants exposed to French marigold essential oil, and glutathione molecules were involved in the mitigation of induced oxidative burst.

Comparative transcriptome analysis in two contrasting genotypes for Sclerotinia sclerotiorum resistance in sunflower

Sclerotinia sclerotiorum as a necrotrophic fungus causes the devastating diseases in many important oilseed crops worldwide. The preferred strategy for controlling S. sclerotiorum is to develop resistant varieties, but the molecular mechanisms underlying S. sclerotiorum resistance remain poorly defined in sunflower (Helianthus annuus). Here, a comparative transcriptomic analysis was performed in leaves of two contrasting sunflower genotypes, disease susceptible (DS) B728 and disease resistant (DR) C6 after S. sclerotiorum inoculation. At 24 h post-inoculation, the DR genotype exhibited no visible growth of the hyphae as well as greater activity of superoxide dismutase activity (SOD), peroxidase (POD), catalase (CAT), glutathione-S-transferase (GST), ascorbate peroxidase (APX) and monodehydroascorbate reductase (MDAR) than DS genotype. A total of 10151 and 7439 differentially expressed genes (DEGs) were detected in DS and DR genotypes, respectively. Most of DEGs were enriched in cell wall organisation, protein kinase activity, hormone, transcription factor activities, redox homeostasis, immune response, and secondary metabolism. Differential expression of genes involved in expansins, pectate lyase activities, ethylene biosynthesis and signaling and antioxidant activity after S. sclerotiorum infection could potentially be responsible for the differential resistance among two genotypes. In summary, these finding provide additional insights into the potential molecular mechanisms of S. sclerotiorum's defense response and facilitate the breeding of Sclerotinia-resistant sunflower varieties.

Effects of endophytes on early growth and ascorbate metabolism in Brassica napus

Understanding the early interactions between plants and endophytes will contribute to a more systematic approach to enhancing endophyte-mediated effects on plant growth and environmental stress resistance. This study examined very early growth and ascorbate metabolism after seed treatment of Brassica napus with three different endophytes. The three endophytes used were Bacillus amyloliquefaciens pb1(Bapb1), Micrococcus luteus (Ml) and Pseudomonas fluorescens SLB4 (SLB4). Seeds of Brassica napus cv. trophy were surface sterilized and plated on 1/2 MS Basal salts (pH 5.7 -5.8) + 0.8% agarose. Under sterile conditions, endophyte suspensions or sterile distilled water (controls) were applied to plated seeds. After two days, all plates were scanned to produce digital images for subsequent growth analysis. Then, seedlings were gently removed from the plates and placed in sterile microfuge tubes. For biochemical analyses, extracts were prepared from samples and assayed spectrophotometrically. We detected slight changes in seedling root tip and/or primary root growth with Bapb1 and Ml. Seedlings treated with SLB4 exhibited significantly increased primary root and root tip length after two days of growth. Ascorbate oxidation, however, was the primary significant change common to all endophyte-treated seedlings. In relation to ascorbate oxidation, soluble ascorbate oxidase (AO) was slightly reduced in Bapb1 and Ml-treated seedlings, whereas ionically-bound AO was reduced in Bapb1 and SLB4-treated seedlings. Total AO activity was significantly reduced in Bapb1-treated seedlings. There were no differences in cytosolic APX activity or glutathione levels between endophyte-treated seedlings and controls. Like pathogens, endophytes can trigger an oxidative burst in the plant. A level of ascorbate oxidation seems required to propagate ROS as signaling molecules as part of the plant immune response. The slight to moderate reductions in plant AO activity that we found mimic the inhibitory effects of pathogens on AO activity, but there was still a level of AO activity that may have been sufficient for the apoplastic ascorbate oxidation required for subsequent ROS signaling. Other studies have suggested that endophytes may elicit a more moderate plant immune response relative to pathogens to facilitate colonization. The AO, APX, and glutathione results would be consistent with a moderate plant immune response to endophytes.

The evolutive role of shoot apical meristems in the adaptation of angiosperms to life at sea and the jump to potential environmental biotechnology applications

Seagrasses have adapted to a submerged lifestyle in seawater through a complex set of evolutionary processes. However, they show sensitivity to increases in natural salinity levels such as those commonly found in discharges of desalination plants, which have exponentially grown due to water scarcity in highly populated temperate areas, such as the Mediterranean basin. This study assessed the effects of brine-derived hypersalinity on the Mediterranean seagrass Posidonia oceanica, focusing on the metabolic responses of shoot apical meristems (SAMs). Although most physiological and genetic studies have used leaves, SAMs are more directly correlated with plant survival and might be more responsive to salinity stress. The experiments were: a controlled mesocosm of more than six practical salinity units (psu) over natural levels using either artificial salts or desalination brine and field transplantation experiments comparing two sites following the dilution plume of the brine (+5 and + 2 psu) with control. Hydrogen peroxide (H2O2), thiobarbituric acid reactive substances (TBARS), and ascorbate were measured to determine oxidative stress and damage, as well as relative expression of genes related to osmotic regulation and oxidative responses. Overall, relative expression of genes related to osmotic regulation (SOS1, SOS3, AKT 2/3) and oxidative stress (STRK1, CAT, MnSOD, FeSOD, APX, GR) was higher in SAMs at higher brine exposures, indicating a more active metabolic response in this organ. Similarly, reactive oxygen species (ROS) production and lipid peroxidation were higher closer to brine discharge and total ascorbate lower, indicating a correlative response with stressor intensity. These findings confirm that SAMs play an essential role in P. oceanica hypersalinity responses and its adaptation to life in the marine environment. Finally, the use of P. oceanica SAMs in this study is highly recommended for an early detection of threats caused by desalination brines that may cause physiological damage and meadow regression.

The regulatory roles of a plant neurotransmitter, acetylcholine, on growth, PSII photochemistry and antioxidant systems in wheat exposed to cadmium and/or mercury stress

Heavy metals increase in nature due to anthropogenic activities and negatively impact the growth, progress, and efficiency of plants. Among the toxic metal pollutants that can cause dangerous effects when accumulated by plants, mercury (Hg) and cadmium (Cd) were investigated in this study. These metals typically inhibit important enzymes and halt their functioning, thereby adversely affecting the capability of plants to achieve photosynthesis, respiration, and produce quality crops. Acetylcholine (ACh) serves as a potent neurotransmitter present in both primitive and advanced plant species. Its significant involvement in diverse metabolic processes, particularly in regulating growth and adaptation to stress, needs to be further elucidated. For this aim, effects of acetylcholine (ACh1, 10 μM; ACh2, 100 μM) were survey in Triticum aestivum under Hg and/or Cd stress (Hg, 50 μM; Cd, 100 μM). Wheat seedlings exhibited a growth retardation of about 24% under Hg or Cd stress. Combined stress conditions (Cd + Hg) resulted in a decrease in RWC by approximately 16%. Two different doses of ACh treatment to stressed plants positively affected growth parameters and regulated the water relations. Gas exchange was limited in stress groups, and the photochemical quantum competency of PSII (Fv/Fm) was suppressed. Cd + ACh1 and Cd + ACh2 treatments resulted in approximately 2-fold and 1.5-fold improvement in stomatal conductance and carbon assimilation rate, respectively. Similarly, improvement was observed with ACh treatments in wheat seedlings under Hg stress. Under Cd and/or Hg stress, high levels of H2O2 accumulated and lipid peroxidation occurred. According to our results, ACh treatment upon Cd and Hg stresses improved the activities of SOD, POX, and APX, thereby reducing oxidative damage. In conclusion, ACh treatment was found to ensure stress tolerance and limit the adverse effects caused by heavy metals.

Unravelling soybean responses to early and late Tetranychus urticae (Acari: Tetranychidae) infestation

Soybean is a crucial source of food, protein, and oil worldwide that is facing challenges from biotic stresses. Infestation of Tetranychus urticae Koch (Acari: Tetranychidae) stands out as detrimentally affecting plant growth and grain production. Understanding soybean responses to T. urticae infestation is pivotal for unravelling the dynamics of mite-plant interactions. We evaluated the physiological and molecular responses of soybean plants to mite infestation after 5 and 21 days. We employed visual/microscopy observations of leaf damage, H2O2 accumulation, and lipid peroxidation. Additionally, the impact of mite infestation on shoot length/dry weight, chlorophyll concentration, and development stages was analysed. Proteomic analysis identified differentially abundant proteins (DAPs) after early (5 days) and late (21 days) infestation. Furthermore, GO, KEGG, and protein-protein interaction analyses were performed to understand effects on metabolic pathways. Throughout the analysed period, symptoms of leaf damage, H2O2 accumulation, and lipid peroxidation consistently increased. Mite infestation reduced shoot length/dry weight, chlorophyll concentration, and development stage duration. Proteomics revealed 185 and 266 DAPs after early and late mite infestation, respectively, indicating a complex remodelling of metabolic pathways. Photorespiration, chlorophyll synthesis, amino acid metabolism, and Krebs cycle/energy production were impacted after both early and late infestation. Additionally, specific metabolic pathways were modified only after early or late infestation. This study underscores the detrimental effects of mite infestation on soybean physiology and metabolism. DAPs offer potential in breeding programs for enhanced resistance. Overall, this research highlights the complex nature of soybean response to mite infestation, providing insights for intervention and breeding strategies.

Ascorbic acid metabolism: New knowledge on mitigation of aluminum stress in plants

Ascorbic acid (ASC) is an important antioxidant in plant cells, being the main biosynthesis pathway is L-galactose or Smirnoff-Wheeler. ASC is involved in plant growth and development processes, being a cofactor and regulator of multiple signaling pathways in response to abiotic stresses. Aluminum toxicity is an important stressor under acidic conditions, affecting plant root elongation, triggering ROS induction and accumulation of hydrogen peroxide (H2O2). To mitigate damage from Al-toxicity, plants have evolved mechanisms to resist stress conditions, such as Al-tolerance and Al-exclusion or avoidance, both strategies related to the forming of non-phytotoxic complexes or bind-chelates among Al and organic molecules like oxalate. Dehydroascorbate (DHA) degradation generates oxalate when ASC is recycled, and dehydroascorbate reductase (DHAR) expression is inhibited. An alternative strategy is ASC regeneration, mainly due to a higher level of DHAR gene expression and low monodehydroascorbate reductase (MDHAR) gene expression. Therefore, studies performed on Fagopyrum esculentum, Nicotiana tabacum, Poncirus trifoliate, and V. corymbosum suggest that ASC is associated with the Al-resistant mechanism, given the observed enhancements in defense mechanisms, including elevated antioxidant capacity and oxalate production. This review examines the potential involvement of ASC metabolism in Al-resistant mechanisms.

Biofortifying multiple micronutrients and decreasing arsenic accumulation in rice grain simultaneously by expressing a mutant allele of OAS-TL gene

Rice grains typically contain relatively high levels of toxic arsenic (As) but low levels of essential micronutrients. Biofortification of essential micronutrients while decreasing As accumulation in rice would benefit human nutrition and health. We generated transgenic rice expressing a gain-of-function mutant allele astol1 driven by the OsGPX1 promoter. astol1 encodes a plastid-localized O-acetylserine (thiol) lyase (OAS-TL) with Ser189Asn substitution (OsASTOL1S189N), which enhances cysteine biosynthesis by forming an indissociable cysteine synthase complex with its partner serine acetyltransferase (SAT). The effects on growth, As tolerance, and nutrient and As accumulation in rice grain were evaluated in hydroponic, pot and field experiments. The expression of OsASTOL1S189N in pOsGPX1::astol1 transgenic lines enhanced SAT activity, sulphate uptake, biosynthesis of cysteine, glutathione, phytochelatins and nicotianamine, and enhanced tolerance to As. The expression of OsASTOL1S189N decreased As accumulation while increased the accumulation of multiple macronutrients (especially sulphur, nitrogen and potassium) and micronutrients (especially zinc and selenium) in rice grain in a pot experiment and two field experiments, and had little effect on plant growth and grain yield. Our study provides a new strategy to genetically engineer rice to biofortify multiple essential nutrients, reducing As accumulation in rice grain and enhancing As tolerance simultaneously.

A Golgi vesicle-membrane-localized cytochrome B561 regulates ascorbic acid regeneration and confers Verticillium wilt resistance in cotton

Ascorbic acid (AsA) serves as a key antioxidant involved in the various physiological processes and against diverse stresses in plants. Due to the insufficiency of AsA de novo biosynthesis, the AsA regeneration is essential to supplement low AsA synthesis rates. Redox reactions play a crucial role in response to biotic stress in plants; however, how AsA regeneration participates in hydrogen peroxide (H2O2) homeostasis and plant defense remains largely unknown. Here, we identified a Golgi vesicle-membrane-localized cytochrome B561 (CytB561) encoding gene, GhB561-11, involved in AsA regeneration and plant resistance to Verticillium dahliae in cotton. GhB561-11 was significantly downregulated upon V. dahliae attack. Knocking down GhB561-11 greatly enhanced cotton resistance to V. dahliae. We found that suppressing GhB561-11 inhibited the AsA regeneration, elevated the basal level of H2O2, and enhanced the plant defense against V. dahliae. Further investigation revealed that GhB561-11 interacted with the lipid droplet-associated protein GhLDAP3 to collectively regulate the AsA regeneration. Simultaneously silencing GhB561-11 and GhLDAP3 significantly elevated the H2O2 contents and dramatically improved the Verticillium wilt resistance in cotton. The study broadens our insights into the functional roles of CytB561 in regulating AsA regeneration and H2O2 homeostasis. It also provides a strategy by downregulating GhB561-11 to enhance Verticillium wilt resistance in cotton breeding programs.

Glutathione and Ascorbic Acid Accumulation in Mango Pulp Under Enhanced UV-B Based on Transcriptome

Mango (Mangifera indica), a nutritionally rich tropical fruit, is significantly impacted by UV-B radiation, which induces oxidative stress and disrupts physiological processes. This study aimed to investigate mango pulp's molecular and biochemical responses to UV-B stress (96 kJ/mol) from the unripe to mature stages over three consecutive years, with samples collected at 10-day intervals. UV-B stress affected both non-enzymatic parameters, such as maturity index, reactive oxygen species (ROS) levels, membrane permeability, and key enzymatic components of the ascorbate-glutathione (AsA-GSH) cycle. These enzymes included glutathione reductase (GR), gamma-glutamyl transferase (GGT), glutathione S-transferases (GST), glutathione peroxidase (GPX), glucose-6-phosphate dehydrogenase (G6PDH), galactono-1,4-lactone dehydrogenase (GalLDH), ascorbate peroxidase (APX), ascorbate oxidase (AAO), and monodehydroascorbate reductase (MDHAR). Transcriptomic analysis revealed 18 differentially expressed genes (DEGs) related to the AsA-GSH cycle, including MiGR, MiGGT1, MiGGT2, MiGPX1, MiGPX2, MiGST1, MiGST2, MiGST3, MiG6PDH1, MiG6PDH2, MiGalLDH, MiAPX1, MiAPX2, MiAAO1, MiAAO2, MiAAO3, MiAAO4, and MiMDHAR, validated through qRT-PCR. The findings suggest that UV-B stress activates a complex regulatory network in mango pulp to optimize ROS detoxification and conserve antioxidants, offering insights for enhancing the resilience of tropical fruit trees to environmental stressors.

Claroideglomus etunicatum enhances Pteris vittata L. arsenic resistance and accumulation by mediating the rapid reduction and transport of arsenic in roots

Arbuscular mycorrhizal fungi (AMF) have been widely shown to significantly promote the growth and recovery of Pteris vittata L. growth and repair under arsenic stress; however, little is known about the molecular mechanisms by which AMF mediate the efficient uptake of arsenic in this species. To understand how AMF mediate P. vittata arsenic metabolism under arsenic stress, we performed P. vittata root transcriptome analysis before and after Claroideglomus etunicatum (C. etunicatum) colonization. The results showed that after C. etunicatum colonization, P. vittata showed greater arsenic resistance and enrichment, and its dry weight and arsenic accumulation increased by 2.01-3.36 times. This response is attributed to the rapid reduction and upward translocation of arsenic. C. etunicatum enhances arsenic uptake by mediating the MIP, PHT, and NRT transporter families, while also increasing arsenic reduction (PvACR2 direct reduction and vesicular PvGSTF1 reduction). In addition, it downregulates the expression of ABC and P-type ATPase protein families, which inhibits the compartmentalization of arsenic in the roots and promotes its translocation to the leaves. This study revealed the mechanism of C. etunicatum-mediated arsenic hyperaccumulation in P. vittata, providing guidance for understanding the regulatory mechanism of P. vittata.

Zinc Oxide Nanoparticle-Mediated Root Metabolic Reprogramming for Arsenic Tolerance in Soybean

Arsenate (AsV) is absorbed and accumulated by plants, which can affect their physiological activities, disrupt gene expression, alter metabolite content, and influence growth. Despite the potential of zinc oxide nanoparticles (ZnONPs) to mitigate the adverse effects of arsenic stress in plants, the underlying mechanisms of ZnONPs-mediated detoxification of AsV, as well as the specific metabolites and metabolic pathways involved, remain largely unexplored. In this study, we demonstrated root metabolomic profiling of soybean germinating seedlings subjected to 25 μmol L-1 arsenate (Na2HAsO4) and ZnONPs at concentrations of 25 μmol L-1 (ZnO25) and 50 μmol L-1 (ZnO50). The objective of this study was to examine the effects on soybean root metabolomics under AsV toxicity. Metabolomic analysis indicated that 453, 501, and 460 metabolites were significantly regulated in response to AsV, ZnO25, and ZnO50 treatments, respectively, compared to the control. Pathway analysis of the differentially regulated metabolites (DRMs) revealed that the tricarboxylic acid (TCA) cycle, glutathione metabolism, proline and aldarate metabolism, and arginine and proline metabolism were the most statistically enriched pathways in ZnONPs-supplemented plants. These findings suggest that ZnONPs enhance the tolerance response to AsV. Collectively, our results support the hypothesis that ZnONPs fertilization could be a potential strategy for improving soybean crop resilience under AsV stress.

Ascorbic acid: a metabolite switch for designing stress-smart crops

Plant growth and productivity are continually being challenged by a diverse array of abiotic stresses, including: water scarcity, extreme temperatures, heavy metal exposure, and soil salinity. A common theme in these stresses is the overproduction of reactive oxygen species (ROS), which disrupts cellular redox homeostasis causing oxidative damage. Ascorbic acid (AsA), commonly known as vitamin C, is an essential nutrient for humans, and also plays a crucial role in the plant kingdom. AsA is synthesized by plants through the d-mannose/l-galactose pathway that functions as a powerful antioxidant and protects plant cells from ROS generated during photosynthesis. AsA controls several key physiological processes, including: photosynthesis, respiration, and carbohydrate metabolism, either by acting as a co-factor for metabolic enzymes or by regulating cellular redox-status. AsA's multi-functionality uniquely positions it to integrate and recalibrate redox-responsive transcriptional/metabolic circuits and essential biological processes, in accordance to developmental and environmental cues. In recognition of this, we present a systematic overview of current evidence highlighting AsA as a central metabolite-switch in plants. Further, a comprehensive overview of genetic manipulation of genes involved in AsA metabolism has been provided along with the bottlenecks and future research directions, that could serve as a framework for designing "stress-smart" crops in future.

Microplastic accumulation and oxidative stress in sweet pepper (Capsicum annuum Linn.): Role of the size effect

Microplastics (MPs), which are widely dispersed in terrestrial environments, threaten crop growth and human food security. However, plant accumulation and phytotoxicity related to the size effects of MPs remain insufficiently explored. This study investigated the accumulation and toxicity of two sizes of MPs on Capsicum annuum Linn. (C. annuum) through fluorescence tracing and antioxidant defense system assessment. The results revealed that the size of MPs significantly impacts their accumulation characteristics in C. annuum roots, leading to variations in toxic mechanisms, including oxidative stress and damage. Smaller MPs and higher exposure concentrations result in more pronounced growth inhibition. C. annuum roots have a critical size threshold for the absorption of MPs of approximately 1.2 μm. MPs that enter the root tissue exhibit an aggregated form, with smaller-sized MPs displaying a greater degree of aggregation. MP exposure induces oxidative stress in root tissues, with high concentrations of smaller MPs causing lipid peroxidation. Analysis of the IBR values revealed that C. annuum roots utilize ascorbic acid (ASA) to prevent oxidative damage caused by larger MPs. Conversely, smaller MPs primarily induce superoxide dismutase (SOD) and glutathione (GSH). These results emphasize the significant impact of MP size on plant antioxidant defense response mechanisms, laying the foundation for further investigating the implications for human health.

Combination of light quality and melatonin regulates the quality in mustard sprouts

Mustard sprouts is a new form of vegetable product that is gaining attention due to its high content of health-promoting compounds such as glucosinolates. This study investigated the effects of different light qualities (white, red, and blue) alone and in combination with 100 μmol L-1 melatonin on the growth and health-promoting substance content of mustard sprouts. The results showed that white light + melatonin treatment promoted the accumulation of glucosinolates in sprouts (compared with white light increased by 47.89%). The edible fresh weight of sprouts treated with red light + melatonin was the highest, followed by white light + melatonin treatment. In addition, the sprouts treated with blue light + melatonin contained more ascorbic acid, flavonoids, and total phenolics. Therefore, the combined treatment of light quality (especially white light) and melatonin can provide a new strategy to improve the quality of mustard sprouts.

The ascorbate peroxidase-related protein: insights into its functioning in Chlamydomonas and Arabidopsis

We review the newly classified ascorbate peroxidase-related (APX-R) proteins, which do not use ascorbate as electron donor to scavenge H2O2. We summarize recent discoveries on the function and the characterization of the APX-R protein of the green unicellular alga Chlamydomonas reinhardtii and the land plant Arabidopsis thaliana. Additionally, we conduct in silico analyses on the conserved MxxM motif, present in most of the APX-R protein in different organisms, which is proposed to bind copper. Based on these analyses, we discuss the similarities between the APX-R and the class III peroxidases.

Photosynthetic control at the cytochrome b6f complex

Photosynthetic control (PCON) is a protective mechanism that prevents light-induced damage to PSI by ensuring the rate of NADPH and ATP production via linear electron transfer (LET) is balanced by their consumption in the CO2 fixation reactions. Protection of PSI is a priority for plants since they lack a dedicated rapid-repair cycle for this complex, meaning that any damage leads to prolonged photoinhibition and decreased growth. The imbalance between LET and the CO2 fixation reactions is sensed at the level of the transthylakoid ΔpH, which increases when light is in excess. The canonical mechanism of PCON involves feedback control by ΔpH on the plastoquinol oxidation step of LET at cytochrome b6f. PCON thereby maintains the PSI special pair chlorophylls (P700) in an oxidized state, which allows excess electrons unused in the CO2 fixation reactions to be safely quenched via charge recombination. In this review we focus on angiosperms, consider how photo-oxidative damage to PSI comes about, explore the consequences of PSI photoinhibition on photosynthesis and growth, discuss recent progress in understanding PCON regulation, and finally consider the prospects for its future manipulation in crop plants to improve photosynthetic efficiency.

Silicon-mediated resilience: Unveiling the protective role against combined cypermethrin and hymexazol phytotoxicity in tomato seedlings

Insecticides and fungicides present potential threats to non-target crops, yet our comprehension of their combined phytotoxicity to plants is limited. Silicon (Si) has been acknowledged for its ability to induce crop tolerance to xenobiotic stresses. However, the specific role of Si in alleviating the cypermethrin (CYP) and hymexazol (HML) combined stress has not been thoroughly explored. This study aims to assess the effectiveness of Si in alleviating phytotoxic effects and elucidating the associated mechanisms of CYP and/or HML in tomato seedlings. The findings demonstrated that, compared to exposure to CYP or HML alone, the simultaneous exposure of CYP and HML significantly impeded seedling growth, resulting in more pronounced phytotoxic effects in tomato seedlings. Additionally, CYP and/or HML exposures diminished the content of photosynthetic pigments and induced oxidative stress in tomato seedlings. Pesticide exposure heightened the activity of both antioxidant and detoxification enzymes, increased proline and phenolic accumulation, and reduced thiols and ascorbate content in tomato seedlings. Applying Si (1 mM) to CYP- and/or HML-stressed seedlings alleviated pigment inhibition and oxidative damage by enhancing the activity of the pesticide metabolism system and secondary metabolism enzymes. Furthermore, Si stimulated the phenylpropanoid pathway by boosting phenylalanine ammonia-lyase activity, as confirmed by the increased total phenolic content. Interestingly, the application of Si enhanced the thiols profile, emphasizing its crucial role in pesticide detoxification in plants. In conclusion, these results suggest that externally applying Si significantly alleviates the physio-biochemical level in tomato seedlings exposed to a combination of pesticides, introducing innovative strategies for fostering a sustainable agroecosystem.