The functions of inter- and intracellular glutathione transport systems in plants

The cadmium tolerance enhancement through regulating glutathione conferred by vacuolar compartmentalization in Aspergillus sydowii

Aspergillus was found to be a vital hyperaccumulation species for heavy metal removal with admirable tolerance capacity. But the potential tolerance mechanism has not been completely studied. This study quantified the amounts of total cadmium (Cd), Cd2+, glutathione (GSH), and reactive oxygen species (ROS) in the protoplasts and vacuoles of mycelium. We modulated GSH synthesis using buthionine sulfoximine (BSO) and 2-oxothiazolidine-4-carboxylic acid (OTC) to investigate the subcellular regulatory mechanisms of GSH in the accumulation of Cd. The results confirmed that GSH plays a crucial role in vacuolar compartmentalization under Cd stress. GSH and GSSG as a redox buffer to keep the cellular redox state in balance and GSH as a metal chelating agent to reduce toxicity. When regulating the decreased GSH content with BSO, and increased GSH content with OTC, the system of Cd-GSH-ROS can change accordingly, this also supported that vacuolar compartmentalization is a detoxification strategy that can modulate the transport and storage of substances inside and outside the vacuole reasonably. Interestingly, GSH tended to be distributed in the cytoplasm, the battleground of redox takes place in the cytoplasm but not in the vacuole. These finding potentially has implications for the understanding of tolerance behavior and detoxification mechanisms of cells. In the future bioremediation of Cd in soil, the efficiency of soil remediation can be improved by developing organisms with high GSH production capacity.

Adaptive responses of nitric oxide (NO) and its intricate dialogue with phytohormones during salinity stress

Nitric oxide (NO) is a gaseous free radical that acts as a messenger for various plant phenomena corresponding to photomorphogenesis, fertilisation, flowering, germination, growth, and productivity. Recent developments have suggested the critical role of NO in inducing adaptive responses in plants during salinity. NO minimises salinity-induced photosynthetic damage and improves plant-water relation, nutrient uptake, stomatal conductance, electron transport, and ROS and antioxidant metabolism. NO contributes active participation in ABA-mediated stomatal regulation. Similar crosstalk of NO with other phytohormones such as auxins (IAAs), gibberellins (GAs), cytokinins (CKs), ethylene (ET), salicylic acid (SA), strigolactones (SLs), and brassinosteroids (BRs) were also observed. Additionally, we discuss NO interaction with other gaseous signalling molecules such as reactive oxygen species (ROS) and reactive sulphur species (RSS). Conclusively, the present review traces critical events in NO-induced morpho-physiological adjustments under salt stress and discusses how such modulations upgrade plant resilience.

Influence of synthetic and natural microfibers on the growth, substance exchange, energy accumulation, and oxidative stress of field-collected microalgae compared with microplastic fragment

Synthetic microfibers (MFs), which are Microplastics (MPs), have not received attention commensurate with their abundance in the environment. Currently, limited studies on MFs have focused on their effects on marine organisms. It is therefore necessary to conduct exposure experiments of MFs on freshwater organisms to provide reference data for the ecological risk assessment of MFs. As a primary producer in freshwater ecosystems, microalgae have an ecological niche that is highly overlapping with that of MFs. In this study, we examined the effects of MFs on the growth of Chlorella and indicators of oxidative stress to examine their potential risk on the microalgae population. The results showed that inhibition rate of microalgae increased with MF concentration in the range of 0.01-100 mg/L. Compared with natural fibers such as cotton and wool, PET and PP fibers showed significant growth inhibition, but less so when in fragment form with the same material and concentration. PP and PET particles, whether fibers or fragments, increased the total antioxidant capacity of microalgal cells and caused oxidative damage. To determine the influence of MFs on the interaction of cells in the environment, the exchanged substances and accumulated energy of microalgae cells were also detected. The results indicated that PP and PET fibers, as well as fragments, increased the diameter and membrane permeability of microalgae cell, thus interfering with the cell division and substance exchange processes. PET fibers and fragments showed different interactions at the level of individual cells and populations. This suggests that the evaluation of MPs should consider examinations from cells to population and even community levels in the future.

Advanced biotechnology strategies for detoxification of persistent organic pollutants and toxic elements in soil

This paper aims to comprehensively examine and present the current state of persistent organic pollutants (POPs) and toxic elements (TEs) in soil. Additionally, it seeks to assess the viability of employing advanced biotechnology, specifically phytoremediation with potent microbial formulations, as a means of detoxifying POPs and TEs. In the context of the "global treaty," which is known as the Stockholm Convention, we analyzed the 3D chemical structures of POPs and its prospects for living organisms which have not been reviewed up to date. The obstacles associated with the phytoremediation strategy in biotechnology, including issues like slow plant growth and limited efficiency in contaminant uptake, have also been discussed and demonstrated. While biotechnology is recognized as a promising method for detoxifying persistent organic pollutants (POPs) and facilitating the restoration of contaminated and degraded lands, its full potential in the field is constrained by various factors. Recent advances in biotechnology, such as microbial enzymes, designer plants, composting, and nanobiotechnology techniques, have opened up new avenues for mitigating persistent organic pollutants (POPs) and toxic elements (TEs). The insights gained from this review can contribute to the development of innovative, practical, and economically viable approaches for remediating and restoring soils contaminated with persistent organic pollutants (POPs) and toxic elements (TEs). The ultimate aim is to reduce the risks to both human and environmental health.

Research advances in mechanisms of arsenic hyperaccumulation of Pteris vittata: Perspectives from plant physiology, molecular biology, and phylogeny

Pteris vittata, as the firstly discovered arsenic (As) hyperaccumulator, has great application value in As-contaminated soil remediation. Currently, the genes involved in As hyperaccumulation in P. vittata have been mined continuously, while they have not been used in practice to enhance phytoremediation efficiency. Aiming to better assist the practice of phytoremediation, this review collects 130 studies to clarify the progress in research into the As hyperaccumulation process in P. vittata from multiple perspectives. Antioxidant defense, rhizosphere activities, vacuolar sequestration, and As efflux are important physiological activities involved in As hyperaccumulation in P. vittata. Among related 19 genes, PHT, TIP, ACR3, ACR2 and HAC family genes play essential roles in arsenate (AsⅤ) transport, arsenite (AsⅢ) transport, vacuole sequestration of AsⅢ, and the reduction of AsⅤ to AsⅢ, respectively. Gene ontology enrichment analysis indicated it is necessary to further explore genes that can bind to related ions, with transport activity, or with function of transmembrane transport. Phylogeny analysis results implied ACR2, HAC and ACR3 family genes with rapid evolutionary rate may be the decisive factors for P. vittata as an As hyperaccumulator. A deeper understanding of the As hyperaccumulation network and key gene components could provide useful tools for further bio-engineered phytoremediation.

Cadmium Absorption in Various Genotypes of Rice under Cadmium Stress

Cadmium (Cd) is a kind of heavy metal. Cadmium pollution in paddy fields will accumulate a large amount of cadmium in rice, which will affect the growth and development of rice. In addition, long-term consumption of rice contaminated with Cd can harm human health. In this study, four rice varieties with high Cd accumulation (S4699, TLY619, JHY1586, QLY155) and four varieties with low Cd accumulation (YY4949, CYJ-7, G8YXSM, MXZ-2) were screened through field experiments for two consecutive years (2021 and 2022) and differences in antioxidant enzyme systems and expression of genes in their organs were analyzed. The total Cd content showed as follows: indica rice > japonica rice, high-Cd-accumulation variety > low-Cd-accumulation variety, and the total Cd content of each organ of rice showed root > stem > leaf > grain. The results of the antioxidant enzyme system showed that the contents of malondialdehyde (MAD), reduced glutathione (GSH), oxidized glutathione (GSSH), and peroxidase (POD) were positively correlated with the total Cd content in rice, and superoxide dismutase (SOD) showed the opposite performance in the leaves. There was no correlation between catalase (CAT) and Cd content, but CAT content decreased in leaves and grains and increased in roots and stems with increasing fertility. Based on this study, RT-qPCR was used to further validate the expression of Cd-uptake-related genes in different rice varieties. It was found that high expression of OsHMA3, OsCCX2, OsNRAMP5, and OsHMA9 genes promoted Cd uptake and translocation in rice, especially in rice varieties with high Cd accumulation. The high expression of OslRT1, OsPCR1, and OsMTP1 genes hindered Cd uptake by rice plants, which was especially evident in low-accumulating Cd rice varieties. These results provide an important theoretical reference and scientific basis for our in-depth study and understanding of the mechanism of cadmium stress tolerance in rice.

Glutathione Contribution in Interactions between Turnip mosaic virus and Arabidopsis thaliana Mutants Lacking Respiratory Burst Oxidase Homologs D and F

Respiratory burst oxidase homologs (Rbohs) play crucial and diverse roles in plant tissue-mediated production of reactive oxygen species during the development, growth, and response of plants to abiotic and biotic stress. Many studies have demonstrated the contribution of RbohD and RbohF in stress signaling in pathogen response differentially modulating the immune response, but the potential role of the Rbohs-mediated response in plant-virus interactions remains unknown. The present study analyzed, for the first time, the metabolism of glutathione in rbohD-, rbohF-, and rbohD/F-transposon-knockout mutants in response to Turnip mosaic virus (TuMV) infection. rbohD-TuMV and Col-0-TuMV interactions were characterized by susceptible reaction to TuMV, associated with significant activity of GPXLs (glutathione peroxidase-like enzymes) and induction of lipid peroxidation in comparison to mock-inoculated plants, with reduced total cellular and apoplastic glutathione content observed at 7-14 dpi and dynamic induction of apoplast GSSG (oxidized glutathione) at 1-14 dpi. Systemic virus infection resulted in the induction of AtGSTU1 and AtGSTU24, which was highly correlated with significant downregulation of GSTs (glutathione transferases) and cellular and apoplastic GGT (γ-glutamyl transferase) with GR (glutathione reductase) activities. On the contrary, resistant rbohF-TuMV reactions, and especially enhanced rbohD/F-TuMV reactions, were characterized by a highly dynamic increase in total cellular and apoplastic glutathione content, with induction of relative expression of AtGGT1, AtGSTU13, and AtGSTU19 genes. Moreover, virus limitation was highly correlated with the upregulation of GSTs, as well as cellular and apoplastic GGT with GR activities. These findings clearly indicate that glutathione can act as a key signaling factor in not only susceptible rbohD reaction but also the resistance reaction presented by rbohF and rbohD/F mutants during TuMV interaction. Furthermore, by actively reducing the pool of glutathione in the apoplast, GGT and GR enzymes acted as a cell first line in the Arabidopsis-TuMV pathosystem response, protecting the cell from oxidative stress in resistant interactions. These dynamically changed signal transductions involved symplast and apoplast in mediated response to TuMV.

The Glutathione S-Transferase PtGSTF1 Improves Biomass Production and Salt Tolerance through Regulating Xylem Cell Proliferation, Ion Homeostasis and Reactive Oxygen Species Scavenging in Poplar

Glutathione S-transferases (GSTs) play an essential role in plant cell detoxification and secondary metabolism. However, their accurate functions in the growth and response to abiotic stress in woody plants are still largely unknown. In this work, a Phi class Glutathione S-transferase encoding gene PtGSTF1 was isolated from poplar (P. trichocarpa), and its biological functions in the regulation of biomass production and salt tolerance were investigated in transgenic poplar. PtGSTF1 was ubiquitously expressed in various tissues and organs, with a predominant expression in leaves and inducible expression by salt stress. Transgenic poplar overexpressing PtGSTF1 showed improved shoot growth, wood formation and improved salt tolerance, consistent with the increased xylem cell number and size under normal condition, and the optimized Na⁺ and K⁺ homeostasis and strengthened reactive oxygen species scavenging during salt stress. Further transcriptome analyses demonstrated that the expressions of genes related to hydrolase, cell wall modification, ion homeostasis and ROS scavenging were up- or down-regulated in transgenic plants. Our findings imply that PtGSTF1 improves both biomass production and salt tolerance through regulating hydrolase activity, cell wall modification, ion homeostasis and ROS scavenging in transgenic poplar, and that it can be considered as a useful gene candidate for the genetic breeding of new tree varieties with improved growth under salt stress conditions.

Selenium Uptake, Transport, Metabolism, Reutilization, and Biofortification in Rice

Selenium (Se) is an essential trace element for humans and other animals. The human body mainly acquires Se from plant foods, especially cereal grains. Rice is the staple food for more than half of the world's population. Increasing the Se concentration of rice grains can increase the average human dietary Se intake. This review summarizes recent advances in the molecular mechanisms of Se uptake, transport, subcellular distribution, retranslocation, volatilization, and Se-containing protein degradation in plants, especially rice. The strategies for improving Se concentration in rice grains by increasing Se accumulation, reducing Se volatilization, and optimizing Se form were proposed, which provide new insight into Se biofortification in rice by improving the utilization efficiency of Se.

Interaction between Melatonin and NO: Action Mechanisms, Main Targets, and Putative Roles of the Emerging Molecule NOmela

Melatonin (MEL), a ubiquitous indolamine molecule, has gained interest in the last few decades due to its regulatory role in plant metabolism. Likewise, nitric oxide (NO), a gasotransmitter, can also affect plant molecular pathways due to its function as a signaling molecule. Both MEL and NO can interact at multiple levels under abiotic stress, starting with their own biosynthetic pathways and inducing a particular signaling response in plants. Moreover, their interaction can result in the formation of NOmela, a very recently discovered nitrosated form of MEL with promising roles in plant physiology. This review summarizes the role of NO and MEL molecules during plant development and fruit ripening, as well as their interactions. Due to the impact of climate-change-related abiotic stresses on agriculture, this review also focuses on the role of these molecules in mediating abiotic stress tolerance and the main mechanisms by which they operate, from the upregulation of the entire antioxidant defense system to the post-translational modifications (PTMs) of important molecules. Their individual interaction and crosstalk with phytohormones and H₂S are also discussed. Finally, we introduce and summarize the little information available about NOmela, an emerging and still very unknown molecule, but that seems to have a stronger potential than MEL and NO separately in mediating plant stress response.

Response of glutathione pools to cadmium stress and the strategy to translocate cadmium from roots to leaves (Daucus carota L.)

Carrots are one of the most highly consumed vegetables in the world. Due to the large area of cadmium (Cd) contaminated farmland, to abate the impact of Cd contamination on carrot quality and safety, a novel strategy is required to drive Cd translocation from the soil to the overground leafy tissues of carrots to protect the edible roots and thus ensure food security. To this end, this article presents an experimental study with mathematical models to assess the tolerance and accumulation capacity of Cd in inedible carrot leaves, as well as the regulatory factors affecting Cd distribution in carrots. The glutathione (GSH) pools were examined in carrot leaves in response to the oxidation stress induced by Cd exposures, and it was found that under low Cd stress (1 and 3 mg/L) the changes of GSH pools were dominated by the variation of GSH, showing higher GSH content and low levels of oxidized GSH content (GSSG). In contrast, both of these two indicator variables as well as the GSH/GSSG ratio all decreased under high Cd stress (5 and 9 mg/L). Combining this information with Cd concentrations in leaves, a model was established to predict the Cd accumulation capacity of leaves. The data showed that the potential Cd accumulation in carrot leaves could be as high as 514 μg/kg dry weight. Furthermore, the factors and primary physiological indicators affecting and regulating GSH pools by multiple stepwise regression were analyzed. The results showed that increasing chlorophyll a/b ratio and γ-glutamylcyclotransferase activity while inhibiting phytochelatin synthase activity could expand the tolerance of carrot leaves to Cd. These findings suggest a possible strategy for regulating the distribution of toxic metals in plants through a molecular-based approach and provide some important information that could be conducive to achieving food safety and phytoremediation of contaminated soils.

Important Roles of Thiols in Methylmercury Uptake and Translocation by Rice Plants

The bioaccumulation of the neurotoxin methylmercury (MeHg) in rice is a significant concern due to its potential risk to humans. Thiols have been known to affect MeHg bioavailability in microorganisms, but how thiols influence MeHg accumulation in rice plants remains unknown. Here, we investigated effects of common low-molecular-weight thiols, including cysteine (Cys), glutathione (GSH), and penicillamine (PEN), on MeHg uptake and translocation by rice plants. Results show that rice roots can rapidly take up MeHg, and this process is influenced by the types and concentrations of thiols in the system. The presence of Cys facilitated MeHg uptake by roots and translocation to shoots, while GSH could only promote MeHg uptake, but not translocation, by roots. Conversely, PEN significantly inhibited MeHg uptake and translocation to shoots. Using labeled ¹³Cys assays, we also found that MeHg uptake was coupled with Cys accumulation in rice roots. Moreover, analyses of comparative transcriptomics revealed that key genes associated with metallothionein and SULTR transporter families may be involved in MeHg uptake. These findings provide new insights into the uptake and translocation of MeHg in rice plants and suggest potential roles of thiol attributes in affecting MeHg bioavailability and bioaccumulation in rice.

Insight into the Vacuolar Compartmentalization Process and the Effect Glutathione Regulation to This Process in the Hyperaccumulator Plant Solanum nigrum L

Vacuole compartmentalization plays an important role in the storage of heavy metals in hyperaccumulators. Is the vacuolar compartmentation a simple shielding process or a dynamic process that continuously consumes cell sap resources? How does glutathione affect the process of vacuolar compartmentalization? These unknown questions are very important to understand the mechanism of vacuole compartmentalization and can provide a guide for the design of hyperaccumulator plants by genetic engineering. Therefore, this study explored the enzyme activities, total cadmium, Cd²⁺, glutathione, oxidized glutathione, and reactive oxygen species contents in protoplasts and vacuoles of leaf cells in Solanum nigrum L. through subcellular separation. The results showed that vacuolar compartmentalization was a dynamic process that actively induced the related substances produced by cell sap to enter the vacuole for detoxification. When regulating the decreased glutathione content with buthionine sulfoximine, the total cadmium and combined cadmium in protoplasm decreased significantly, but the vacuole still maintained a high proportion of cadmium content and stable ROS content, which indicated that various external resources were preferentially used to maintain cadmium storage and homeostasis in vacuole rather than outside vacuole. These findings could guide the use of genetic engineering to design hyperaccumulator plants.

The Interplay between Hydrogen Sulfide and Phytohormone Signaling Pathways under Challenging Environments

Hydrogen sulfide (H₂S) serves as an important gaseous signaling molecule that is involved in intra- and intercellular signal transduction in plant–environment interactions. In plants, H₂S is formed in sulfate/cysteine reduction pathways. The activation of endogenous H₂S and its exogenous application has been found to be highly effective in ameliorating a wide variety of stress conditions in plants. The H₂S interferes with the cellular redox regulatory network and prevents the degradation of proteins from oxidative stress via post-translational modifications (PTMs). H₂S-mediated persulfidation allows the rapid response of proteins in signaling networks to environmental stimuli. In addition, regulatory crosstalk of H₂S with other gaseous signals and plant growth regulators enable the activation of multiple signaling cascades that drive cellular adaptation. In this review, we summarize and discuss the current understanding of the molecular mechanisms of H₂S-induced cellular adjustments and the interactions between H₂S and various signaling pathways in plants, emphasizing the recent progress in our understanding of the effects of H₂S on the PTMs of proteins. We also discuss future directions that would advance our understanding of H₂S interactions to ultimately mitigate the impacts of environmental stresses in the plants.

Glutathione Modulation in PVYNTN Susceptible and Resistant Potato Plant Interactions

Glutathione is a metabolite that plays an important role in plant response to biotic stress through its ability to remove reactive oxygen species, thereby limiting the degree of potential oxidative damage. It can couple changes in the intracellular redox state to the development, especially the defense responses, of plants. Several studies have focused on measuring glutathione levels in virus infected plants, but have not provided complete information. Therefore, we analyzed, for the first time, the content of glutathione as well as its ultrastructural distribution related to susceptible and hypersensitive potato–Potato virus Y NTN (PVY^NTN) interaction, with an aim of providing new insight into interactive responses to PVY^NTN stress. Our findings reported that the inoculation of PVY^NTN caused a dynamic increase in the content of glutathione, not only in resistance but also in susceptible reaction, especially at the first steps of plant–virus interaction. Moreover, the increase in hypersensitive response was much more dynamic, and accompanied by a significant reduction in the content of PVY^NTN. By contrast, in susceptible potato Irys, the content of glutathione decreased between 7 and 21 days after virus inoculation, which led to a significant increase in PVY^NTN concentration. Additionally, our findings clearly indicated the steady induction of two selected potato glutathione S-transferase StGSTF1 and StGSTF2 genes after PVY^NTN inoculation, regardless of the interaction type. However, the relative expression level of StGSTF1 did not significantly differ between resistant and susceptible plants, whereas the relative expression levels of StGSTF2 differed between susceptible and resistant reactions. Therefore, we proposed that StGSTF2 can act as a marker of the type of response to PVY^NTN. Our observations indicated that glutathione is an important component of signaling as well as the regulatory network in the PVY^NTN–potato pathosystem. In resistance responses to PVY^NTN, this metabolite activates plant defenses by reducing potential damage to the host plant cell, causing a reduction in virus concentration, while it can also be involved in the development of PVY^NTN elicited symptoms, as well as limiting oxidative stress, leading to systemic infection in susceptible potato plants.

Fluorescence Probes for Reactive Sulfur Species in Agricultural Chemistry

Sulfur is an element that is indispensable throughout the growth of plants. In plant cells, reactive sulfur species (RSS) play a vital role in maintaining cellular redox homeostasis and signal transduction. There is demand accordingly for a simple, highly selective, and sensitive method of RSS detection and imaging for monitoring dynamic changes and clarifying the biological functions of RSS in plant systems. Fluorescent analysis based on organic small-molecule fluorescent probes is an effective and specific approach to tracking plant RSS characteristics. This perspective summarizes the recent progress regarding organic small-molecule fluorescent probes for RSS monitoring, including small-molecule biological thiols, hydrogen sulfide, and sulfane sulfurs, in plants; it also discusses their response mechanism toward RSS and their imaging applications in plants across the agricultural chemistry field.

Proteins, Small Peptides and Other Signaling Molecules Identified as Inconspicuous but Possibly Important Players in Microspores Reprogramming Toward Embryogenesis

In this review, we describe and integrate the latest knowledge on the signaling role of proteins and peptides in the stress-induced microspore embryogenesis (ME) in some crop plants with agricultural importance (i.e., oilseed rape, tobacco, barley, wheat, rice, triticale, rye). Based on the results received from the most advanced omix analyses, we have selected some inconspicuous but possibly important players in microspores reprogramming toward embryogenic development. We provide an overview of the roles and downstream effect of stress-related proteins (e.g., β-1,3-glucanases, chitinases) and small signaling peptides, especially cysteine—(e.g., glutathione, γ-thionins, rapid alkalinization factor, lipid transfer, phytosulfokine) and glycine-rich peptides and other proteins (e.g., fasciclin-like arabinogalactan protein) on acclimation ability of microspores and the cell wall reconstruction in a context of ME induction and haploids/doubled haploids (DHs) production. Application of these molecules, stimulating the induction and proper development of embryo-like structures and green plant regeneration, brings significant improvement of the effectiveness of DHs procedures and could result in its wider incorporation on a commercial scale. Recent advances in the design and construction of synthetic peptides–mainly cysteine-rich peptides and their derivatives–have accelerated the development of new DNA-free genome-editing techniques. These new systems are evolving incredibly fast and soon will find application in many areas of plant science and breeding.

Visualization and quantification of cadmium accumulation, chelation and antioxidation during the process of vacuolar compartmentalization in the hyperaccumulator plant Solanum nigrum L

Hyperaccumulators store metals in the vacuoles of leaf cells. To investigate the role of vacuolar compartmentalization in Cd accumulation, chelation and induced antioxidation, we quantified the amounts of total cadmium (Cd), Cd²⁺, glutathione (GSH) and reactive oxygen species (ROS) in leaf cells of Solanum nigrum L. The results confirmed that vacuoles were, indeed, the main storage compartments for Cd. We then found that with increased Cd treatment concentration, the proportion of vacuolar Cd in protoplasts showed its ultimate storage capacity (82.24 %-83.40 %), and the Cd concentration stored in the protoplast maintained at a certain level (73.81-77.46 mg L^-1). Besides, studies on different forms of Cd showed that the chelation state was dominant in the protoplast. The large level appearance of Cd²⁺ outside the vacuole revealed the limitations of vacuolar Cd²⁺ sequestration. The relationships between the combined forms of Cd and GSH outside the vacuole (R² = 0.9906) showed GSH was mainly distributed to important compartments for chelation, not to vacuoles. We also demonstrated the presence of ROS-induced oxidative stress and detoxification mediated by the antioxidant GSH in vacuoles, suggesting that sequestration into vacuoles is an active process accompanied by chelation and antioxidant-mediated detoxification.

Foliar Nourishment with Nano-Selenium Dioxide Promotes Physiology, Biochemistry, Antioxidant Defenses, and Salt Tolerance in Phaseolus vulgaris

Novel strategic green approaches are urgently needed to raise the performance of plants subjected to stress. Two field-level experimental attempts were implemented during two (2019 and 2020) growing seasons to study the possible effects of exogenous nourishment with selenium dioxide nanoparticles (Se-NPs) on growth, physio-biochemical ingredients, antioxidant defenses, and yield of Phaseolus vulgaris (L.) plant growing on a salt-affected soil (EC = 7.55–7.61 dS m⁻¹). At 20, 30, and 40 days from seeding, three foliar sprays were applied to plants with Se-NPs at a rate of 0.5, 1.0, or 1.5 mM. The experimental design was accomplished in randomized complete plots. The data indicate noteworthy elevations in indicators related to growth and yield; pigments related to effective photosynthesis, osmoprotectant (free proline and soluble sugars), nutrient and Se contents, K⁺/Na⁺ ratio, cell integrity (water content and stability of membranes), all enzyme activities; and all features related to leaf anatomy induced by Se-NPs foliar spray. Conversely, marked lowering in markers of Na⁺ content-induced oxidative stress (superoxide radical and hydrogen peroxide) and their outcomes in terms of ionic leakage and malondialdehyde were reported by foliar nourishment with Se-NPS compared to spraying leaves with water as an implemented control. The best results were recorded with Se-NPs applied at 1.0 mM, which mitigated the negative effects of soil salinity (control results). Therefore, the outcomes of this successful study recommend the use of Se-NPs at a rate of 1.0 mM as a foliar spray to grow common beans on saline soils with EC up to 7.55–7.61 dS m⁻¹.

Effects of florfenicol on growth, photosynthesis and antioxidant system of the non-target organism Isochrysis galbana

Florfenicol (FFC) is one of the most universally used antibiotics in aquaculture, which is substitute for chloramphenicol extensively, while the massive residues in aquatic environment were assumed to threaten the non-target organisms. Present research investigated the effects of florfenicol on growth, chlorophyll content, photosynthesis, and antioxidant ability of Isochrysis galbana. The results showed that FFC at 0.001-1 mg/L stimulated the growth of I. galbana and increased the content of chlorophyll. In addition, photosynthesis of I. galbana was inhibited and the photosynthetic parameters were uplifted with the increased exposure duration and FFC concentration. Furthermore, superoxide dismutase (SOD), catalase (CAT) activity significantly dropped at 0.01-20 mg/L FFC, while the contents of malondialdehyde (MDA), glutathione (GSH) and reactive oxygen species (ROS) increased after 72 h exposure, indicating that FFC at high concentrations caused a serious oxidative stress on algae. The simultaneous increase of ROS disrupted the equilibration between oxidants and antioxidant systems. Under the high concentration of FFC, the excessive of ROS was generated in algae which affected the membrane permeability and further decreased the cell biomass. Present study showed that acute exposure (72 h) at the environmental relevant concentration (0.01 mg/L) cannot induce the physiological dysfunction of the microalgae I. galbana, but the feeding concentration (20 mg/L) can. Additionally, this study hinted the possible negative impacts on ecosystems with the chronic exposure even at low FFC concentration or with the uncontrolled use of FFC.

Sulfonamides-induced oxidative stress in freshwater microalga Chlorella vulgaris: Evaluation of growth, photosynthesis, antioxidants, ultrastructure, and nucleic acids

Sulfadiazine (SD), sulfamerazine (SM1), and sulfamethazine (SM2) are widely used and disorderly discharged into surface water, causing contamination of lakes and rivers. However, microalgae are regard as a potential resource to alleviate and degrade antibiotic pollution. The physiological changes of Chlorella vulgaris in the presence of three sulfonamides (SAs) with varying numbers of –CH₃ groups and its SA-removal efficiency were investigated following a 7-day exposure experiment. Our results showed that the growth inhibitory effect of SD (7.9–22.6%), SM1 (7.2–45.9%), and SM2 (10.3–44%) resulted in increased proteins and decreased soluble sugars. Oxidative stress caused an increase in superoxide dismutase and glutathione reductase levels but decreased catalase level. The antioxidant responses were insufficient to cope-up with reactive oxygen species (hydrogen peroxide and superoxide anion) levels and prevent oxidative damage (malondialdehyde level). The ultrastructure and DNA of SA-treated algal cells were affected, as evident from the considerable changes in the cell wall, chloroplast, and mitochondrion, and DNA migration. C. vulgaris-mediated was able to remove up to 29% of SD, 16% of SM1, and 15% of SM2. Our results suggest that certain concentrations of specific antibiotics may induce algal growth, and algal-mediated biodegradation process can accelerate the removal of antibiotic contamination.

Glutathione redox state plays a key role in flower development and pollen vigour

The importance of the glutathione pool in the development of reproductive tissues and in pollen tube growth was investigated in wild-type (WT) Arabidopsis thaliana, a reporter line expressing redox-sensitive green fluorescent protein (roGFP2), and a glutathione-deficient cad2-1 mutant (cad2-1/roGFP2). The cad2-1/roGFP2 flowers had significantly less reduced glutathione (GSH) and more glutathione disulfide (GSSG) than WT or roGFP2 flowers. The stigma, style, anther, germinated pollen grains, and pollen tubes of roGFP2 flowers had a low degree of oxidation. However, these tissues were more oxidized in cad2-1/roGFP2 flowers than the roGFP2 controls. The ungerminated pollen grains were significantly more oxidized than the germinated pollen grains, indicating that the pollen cells become reduced upon the transition from the quiescent to the metabolically active state during germination. The germination percentage was lower in cad2-1/roGFP2 pollen and pollen tube growth arrested earlier than in roGFP2 pollen, demonstrating that increased cellular reduction is essential for pollen tube growth. These findings establish that ungerminated pollen grains exist in a relatively oxidized state compared with germinating pollen grains. Moreover, failure to accumulate glutathione and maintain a high GSH/GSSG ratio has a strong negative effect on pollen germination.

Effects of enhancing endogenous and exogenous glutathione in roots on cadmium movement in Arabidopsis thaliana

Glutathione (GSH) is a thiol-containing compound involved in many aspects of plant metabolism. In the present study, we investigated how enhancing endogenous and exogenous GSH affects cadmium (Cd) movement and distribution in Arabidopsis plants cultured hydroponically. Transgenic Arabidopsis plants with a strong ability to synthesize GSH in roots were generated　by transforming the gene encoding the bifunctional γ-glutamylcysteine synthetase-glutathione synthetase enzyme from Streptococcus thermophiles (StGCS-GS). Enhancing endogenous and exogenous GSH decreased the Cd translocation ratio in different ways. Only exogenous GSH significantly inhibited Cd translocation from roots to shoots in wild-type and transgenic Arabidopsis plants. Our study demonstrated that GSH mainly functions outside root cells to inhibit Cd translocation from roots to shoots.

Melatonin-Nitric Oxide Crosstalk and Their Roles in the Redox Network in Plants

Melatonin, an amine hormone highly conserved during evolution, has a wide range of physiological functions in animals and plants. It is involved in plant growth, development, maturation, and aging, and also helps ameliorate various types of abiotic and biotic stresses, including salt, drought, heavy metals, and pathogens. Melatonin-related growth and defense responses of plants are complex, and involve many signaling molecules. Among these, the most important one is nitric oxide (NO), a freely diffusing amphiphilic biomolecule that can easily cross the cell membrane, produce rapid signal responses, and participate in a wide variety of physiological reactions. NO-induced S-nitrosylation is also involved in plant defense responses. NO interacts with melatonin as a long-range signaling molecule, and helps regulate plant growth and maintain oxidative homeostasis. Exposure of plants to abiotic stresses causes the increase of endogenous melatonin levels, with the consequent up-regulation of melatonin synthesis genes, and further increase of melatonin content. The application of exogenous melatonin causes an increase in endogenous NO and up-regulation of defense-related transcription factors, resulting in enhanced stress resistance. When plants are infected by pathogenic bacteria, NO acts as a downstream signal to lead to increased melatonin levels, which in turn induces the mitogen-activated protein kinase (MAPK) cascade and associated defense responses. The application of exogenous melatonin can also promote sugar and glycerol production, leading to increased levels of salicylic acid and NO. Melatonin and NO in plants can function cooperatively to promote lateral root growth, delay aging, and ameliorate iron deficiency. Further studies are needed to clarify certain aspects of the melatonin/NO relationship in plant physiology.

Effects of polyethylene microplastic on the phytotoxicity of di-n-butyl phthalate in lettuce (Lactuca sativa L. var. ramosa Hort)

The increase in the proportion of microplastics in the environment has intensified the interest in phthalate and microplastic contamination in recent years. In this study, we investigated the response of photosynthetic parameters and the antioxidant system of lettuce to di-n-butyl phthalate (DBP) stress and exposure to various concentrations of microplastic polyethylene (MP) for different durations (14 d and 28 d). Lettuce growth, photosynthetic parameters, and chlorophyll content were reduced significantly after MP- and DBP-only treatments and after the combined (MP + DBP) treatments with both pollutants (P < 0.05), when compared with the control. Our findings indicated that the exposure to MP can inhibit growth, hinder photosynthesis, and interfere with the antioxidant defense system in lettuce. Specifically, compared with the DBP-only treatment group, in all MP + DBP treatment groups, the lettuce growth parameters (dry and fresh weights of the leaves and roots and the number of leaves) decreased (P < 0.05). Moreover, the photosynthetic rate, stomatal conductance, transient transpiration rate, fluorescence parameters, chlorophyll content of leaves, and activity of Rubisco decreased, but the intercellular CO2 concentration increased in all MP + DBP treatment groups. The reduction in photosynthesis was attributed to the limitation of non-porosity and inhibition of the photoelectron flow, and the increase in exogenous MP content aggravated the effect of DBP on photosynthesis in lettuce. Compared with the DBP-only group, in all MP + DBP treatment groups, the content of superoxide radicals and hydrogen peroxide in lettuce leaves and roots increased. Antioxidant levels increased with the increase in MP content, except in the 1.0 mg mL-1 MP treatment after 14 d. Although the antioxidant system exhibited certain protective effects in the latter treatment, the cell membranes were still damaged. The degree of damage to cells decreased with the growth of lettuce, but the damage to root tissue always remained higher than that of the leaves. In conclusion, exposure to exogenous MP exacerbated the damage to lettuce by DBP.

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

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

Characterization of the cellular effects and mechanism of arsenic trioxide-induced hepatotoxicity in broiler chickens

To characterize the cellular effects and mechanism of arsenic trioxide (ATO)-induced hepatotoxicity in broiler chickens, increasing concentrations of ATO (0, 0.6, 1.2, 2.4, and 4.8 μM) were added to chicken hepatocyte cultures in vitro. The changes in hepatocyte morphology, oxidative stress and apoptosis were evaluated using fluorescence microscopy and flow cytometry. The effects of ATO on mRNA or protein expression of antioxidant enzymes, especially methionine sulfoxide reductase (Msr), were analyzed using qRT-PCR and western blotting assays. Increased apoptosis were concomitant with increased reactive oxygen species (ROS) accumulation and upregulation of antioxidant enzymes such as catalase (CAT) and superoxide dismutase (SOD) with increasing ATO concentrations. Moreover, G₁ phase arrest and dysregulation of the balance between antiapoptotic versus proapoptotic factors were noted. Furthermore, upregulation of HO-1, SOD-1, and TRX in the ATO groups were consistent with ATO-induced oxidative damage. High Msr, SOD-1, TRX, Bak1, Bax, and p53 protein levels in the ATO groups indicate that these proteins may have accumulated to counter ATO-induced oxidative stress. ROS scavenger N-acetyl-l-cysteine (NAC) could reverse ATO-induced oxidative damage and restore hepatocyte viability, even with compromised Msr function. Our findings suggest that Msr can protect broiler hepatocytes against ATO-induced oxidative stress. Furthermore, NAC-mediated reversal of oxidative damage may represent a strategy to mitigate potential economic losses associated with arsenic poisoning in the poultry industry.

Tolerance to Cyclic Desiccation in Lichen Microalgae is Related to Habitat Preference and Involves Specific Priming of the Antioxidant System

Oxidative stress is a crucial challenge for lichens exposed to cyclic desiccation and rehydration (D/R). However, strategies to overcome this potential stress are still being unraveled. Therefore, the physiological performance and antioxidant mechanisms of two lichen microalgae, Trebouxia sp. (TR9) and Coccomyxa simplex (Csol), were analyzed. TR9 was isolated from Ramalina farinacea, a Mediterranean fruticose epiphytic lichen adapted to xeric habitats, while Csol is the phycobiont of Solorina saccata, a foliaceous lichen that grows on humid rock crevices. The tolerance to desiccation of both species was tested by subjecting them to different drying conditions and to four consecutive daily cycles of D/R. Our results show that a relative humidity close to that of their habitats was crucial to maintain the photosynthetic rates. Concerning antioxidant enzymes, in general, manganese superoxide dismutases (MnSODs) were induced after desiccation and decreased after rehydration. In TR9, catalase (CAT)-A increased, and its activity was maintained after four cycles of D/R. Ascorbate peroxidase activity was detected only in Csol, while glutathione reductase increased only in TR9. Transcript levels of antioxidant enzymes indicate that most isoforms of MnSOD and FeSOD were induced by desiccation and repressed after rehydration. CAT2 gene expression was also upregulated and maintained at higher levels even after four cycles of D/R in accordance with enzymatic activities. To our knowledge, this is the first study to include the complete set of the main antioxidant enzymes in desiccation-tolerant microalgae. The results highlight the species-specific induction of the antioxidant system during cyclic D/R, suggesting a priming of oxidative defence metabolism.

First Evidence of the Cysteine and Glutathione Conjugates of 3-Sulfanylpentan-1-ol in Hop ( Humulus lupulus L.)

After evidence of the cysteinylated precursors of 3-sulfanyl-4-methylpentan-1-ol (Cys-26) and 3-sulfanylhexan-1-ol (Cys-23) in hop, S-glutathione precursors (G-23 and G-26) were recently discovered in different dual-purpose hop varieties. Because free 3-sulfanylpentan-1-ol (21) has also been detected in hop, the present work aimed to identify its potential precursors. The compounds S-3-(1-hydroxylpentyl)cysteine (Cys-21) and S-3-(1-hydroxylpentyl)glutathione (G-21) were first synthesized and characterized by nuclear magnetic resonance and high-resolution mass spectrometry. High-performance liquid chromatography-positive electrospray ionization-tandem mass spectrometry evidenced both for the first time in hop. Both S conjugates were further quantitated in six hop samples: the well-known Saaz, Amarillo, Citra, Hallertau Blanc, Nelson Sauvin, and Polaris. Similar to G-23, G-21 appeared ubiquitous to all varieties. Of all of the samples investigated here, Citra (harvest 2017) emerged as the richest in G-21, with 18 mg/kg of dry matter. Cys-21 was found in all samples at a much lower concentration (up to 0.2 mg/kg of dry matter in Polaris, harvest 2017). Model media spiked with Cys-21 or G-21 allowed for the confirmation that brewing yeast is able to release free compound 21 from them.

Integrative moringa and licorice extracts application improves Capsicum annuum fruit yield and declines its contaminant contents on a heavy metals-contaminated saline soil

Green approaches for improving plant performance using natural supplementations are highly seeking. Following a preliminary study conducted on contaminated saline (EC = 7.75 dS m^-1) and normal (EC = 1.4 dS m^-1) soils, two main field trials were conducted to study the potential effects of licorice root (LRE; 0.5%) and moringa seed (MSE; 0.5%) extracts, supplemented to soil through irrigation water (SA) and/or as foliar spray (FS), on performance, physio-biochemical components, antioxidant defense system, and contaminants contents of Capsicum annuum plants grown on heavy metals-contaminated saline soil. Both extracts were applied in single treatments such as LRE-SA, MSE-SA, LRE-FS, and MSE-FS or in integrations like LRE-SA+LRE-FS, LRE-SA+MSE-FS, MSE-SA+LRE-FS, and MSE-SA+MSE-FS. The preliminary study results showed significant reductions in plant performance (growth and yield), chlorophylls content and significant increase in Cd content due to heavy metals and salt stress. However, LRE and MSE applied singly or in combinations positively modified these parameters compared to the control (SA and FS were applied with tap water). On the other hand, these parameters were not responded to LRE and/or MSE applications on the normal soil. The main studies results showed that all single or integrative treatments significantly increased plant growth and yield, leaf contents of leaf photosynthetic pigments, free proline, total soluble sugars, N, P, and K⁺, ratio of K⁺/Na⁺, and activities of CAT, POX, APX, SOD, and GR. In contrast, contaminants; Na⁺, Cd, Cu, Pb and Ni contents in plant leaves and fruits were significantly reduced on heavy metals-contaminated saline soil compared to the control. Additionally, all integrative treatments significantly exceeded all single treatments in this concern. The integrative MSE-SA+LRE-FS was the best treatment that is recommended to be used to maximize pepper plant performances and minimize plant contaminant contents on contaminated saline soils.

Phytomelatonin: Recent advances and future prospects

Melatonin (MEL) has been revealed as a phylogenetically conserved molecule with a ubiquitous distribution from primitive photosynthetic bacteria to higher plants, including algae and fungi. Since MEL is implicated in numerous plant developmental processes and stress responses, the exploration of its functions in plant has become a rapidly progressing field with the new paradigm of involvement in plants growth and development. The pleiotropic involvement of MEL in regulating the transcripts of numerous genes confirms its vital involvement as a multi-regulatory molecule that architects many aspects of plant development. However, the cumulative research in plants is still preliminary and fragmentary in terms of its established functions compared to what is known about MEL physiology in animals. This supports the need for a comprehensive review that summarizes the new aspects pertaining to its functional role in photosynthesis, phytohormonal interactions under stress, cellular redox signaling, along with other regulatory roles in plant immunity, phytoremediation, and plant microbial interactions. The present review covers the latest advances on the mechanistic roles of phytomelatonin. While phytomelatonin is a sovereign plant growth regulator that can interact with the functions of other plant growth regulators or hormones, its qualifications as a complete phytohormone are still to be established. This review also showcases the yet to be identified potentials of phytomelatonin that will surely encourage the plant scientists to uncover new functional aspects of phytomelatonin in plant growth and development, subsequently improving its status as a potential new phytohormone.

Physiological responses to cadmium stress in strawberry treated with pomegranate peel-activated carbon

Many reports have already been published regarding the removal of heavy metals from aqueous solutions onto activated carbon. However, the biosorbents' effect on the plant response still needs further investigation. In this study, activated carbon derived from the pomegranate peel [pomegranate activated carbons (PAC)] was used to see the effects of the addition of PAC on growing strawberry in Cd-contaminated sand. Cd accumulation and toxicity to strawberry was investigated by measuring the concentration of Cd in plant tissues and various biochemical activities of plant. Our results suggested that PAC had a high sorption capacity for Cd. Strawberry plant tried to deal with the Cd-induced oxidative stress by strengthening its antioxidant competences and decreasing Cd absorption. In comparison with the control, PAC applied to the sand decreased the level of lipid peroxidation and enhanced the carotenoid content. The greater tolerance of strawberry toward the level of Cd due to the application of PAC was associated with improving the physical conditions of the soil, increasing the amounts of some essential elements and decreasing the level of Cd absorption. Gaviota strawberry cultivar exposed to 5 or 10 mg kg^-1 Cd was able to adopt a new metabolic equilibrium, allowing the plant to cope with this metal.

Transcriptional and cellular effects of benzotriazole UV stabilizers UV-234 and UV-328 in the freshwater invertebrates Chlamydomonas reinhardtii and Daphnia magna

Benzotriazole ultra violet stabilizers (BZT-UVs) are compounds used in many applications and products to prevent photochemical degradation. Despite their widespread presence in aquatic ecosystems and persistence in the environment, there are very limited data on their effects and toxicity, and their modes of action remain largely unknown. The objectives of the present study were to evaluate the chronic effects of 2 BZT-UVs, 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (UV-234) and 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (UV-328), on the freshwater green algae Chlamydomonas reinhardtii and the freshwater crustacean Daphnia magna. Organisms were exposed to 0.01 and 10 μg/L of UV-234, UV-328, as well as a mixture of the 2 compounds. Life-history endpoints (viability, reproduction, and growth) and oxidative stress-related biomarkers (gene transcription, reactive oxygen species [ROS] production, and lipid peroxidation) were measured. Daphnia magna growth, reproduction, and gene transcription were not impacted by 21-d individual or mixed exposure. After 96-h of exposure, no differences were observed on the cellular viability of C. reinhardtii for either of the 2 BZT-UVs. In the algae, results showed increased ROS production in response to UV-328 and lipid peroxidation following exposure to UV-234. Synergistic effects of the 2 BZT-UVs were evident at the transcriptional level with 2 to 6 times up-regulation of glutathione peroxidase (gp_x ) in response to the mixture for all treatment conditions. The transcription of superoxide dismutase (sod), catalase (cat), and ascorbic peroxidase (apx) was also regulated by UV-234 and UV-328 in the green algae, most likely as a result of ROS production and lipid peroxidation. Results from the present study suggest potential impacts of UV-234 and UV-328 exposure on the antioxidant defense system in C. reinhardtii. Environ Toxicol Chem 2017;36:3333-3342. © 2017 Crown in the Right of Canada. Published by Wiley Periodicals Inc., on behalf of SETAC.

Glutathione Degradation

SIGNIFICANCE

Glutathione degradation has for long been thought to occur only on noncytosolic pools. This is because there has been only one enzyme known to degrade glutathione (γ-glutamyl transpeptidase) and this localizes to either the plasma membrane (mammals, bacteria) or the vacuolar membrane (yeast, plants) and acts on extracellular or vacuolar pools. The last few years have seen the discovery of several new enzymes of glutathione degradation that function in the cytosol, throwing new light on glutathione degradation. Recent Advances: The new enzymes that have been identified in the last few years that can initiate glutathione degradation include the Dug enzyme found in yeast and fungi, the ChaC1 enzyme found among higher eukaryotes, the ChaC2 enzyme found from bacteria to man, and the RipAY enzyme found in some bacteria. These enzymes play roles ranging from housekeeping functions to stress responses and are involved in processes such as embryonic neural development and pathogenesis.

CRITICAL ISSUES

In addition to delineating the pathways of glutathione degradation in detail, a critical issue is to find how these new enzymes impact cellular physiology and homeostasis.

FUTURE DIRECTIONS

Glutathione degradation plays a far greater role in cellular physiology than previously envisaged. The differential regulation and differential specificities of various enzymes, each acting on distinct pools, can lead to different consequences to the cell. It is likely that the coming years will see these downstream effects being unraveled in greater detail and will lead to a better understanding and appreciation of glutathione degradation. Antioxid. Redox Signal. 27, 1200-1216.

Exogenous malic acid alleviates cadmium toxicity in Miscanthus sacchariflorus through enhancing photosynthetic capacity and restraining ROS accumulation

Malic acid (MA) plays an important role in the regulation of plant growth, stomatal aperture, nutrition elements homeostasis and toxic metals tolerance. However, little is known about the effects of exogenous MA on physiological and biochemical responses to toxic metals in plants. To measure the alleviation roles of exogenous MA against cadmium (Cd), we determined the effects of MA on plant growth, net photosynthetic rate (Pn), reactive oxygen species (ROS) accumulation and the activities of anti-oxidant enzymes in the leaves of Miscanthus sacchariflorus (M. sacchariflorus) under Cd stress. The Cd exposure alone significantly inhibited plant growth and Pn, but increased the accumulation of ROS even though the anti-oxidant enzymes were markedly activated in the leaves of M. sacchariflorus. Treatment with MA significantly enhanced plant growth and decreased Cd accumulation accompanied by increasing Pn under Cd stress as compared to Cd stress alone, especially when treatment with high concentration of MA (200μM) was used. In addition, Cd and MA indicated synergistic effects by further increasing the activities and genes expression of partial anti-oxidant enzymes, thus resulting in higher glutathione accumulation and reduction of ROS production. The results showed that application of MA alleviated Cd-induced phytotoxicity and oxidant damage through the regulation of both enzymatic and non-enzymatic anti-oxidants under Cd stress in M. sacchariflorus.

Chronic dietary ginseng extract administration ameliorates antioxidant and cholinergic systems in the brains of aged mice

Background

Black ginseng has a more potent biological activity than non-steamed ginseng. We investigated the effects of long-term intake of dietary black ginseng extract (BG) on antioxidant activity in aged mice. We also compared the effects of BG on cognitive deficits with those of white ginseng extract (WG) and red ginseng extract (RG).

Methods

Ten-month-old mice were fed an AIN-93G-based diet containing 10 g/kg (low dose, L) or 30 g/kg (high dose, H) WG powder, RG powder, or BG powder for 24 wk. We measured serum lipids, the activities of antioxidant enzymes, and malondialdehyde levels. Additionally, the protein expression levels of choline acetyltransferase and vesicular acetylcholine transporter, which are presynaptic cholinergic markers in the cortex and hippocampus of the brain, were measured by western blotting.

Results

Triglyceride levels were reduced in all the extract-treated mice, except those in the LBG group. High-density lipoprotein cholesterol levels in the HBG group were higher than those in the control group. Total cholesterol levels were reduced in the LBG group. Additionally, glucose levels in the HBG group were significantly reduced by 41.2%. There were lower levels of malondialdehyde in the LBG group than in the control group. Furthermore, glutathione reductase activity increased in the HWG group and the HRG group. The protein expression levels of choline acetyltransferase and vesicular acetylcholine transporter significantly increased in all the ginseng-treated groups.

Conclusion

The results suggest that supplementation with the tested ginseng extracts may suppress the cognitive decline associated with aging, via regulation of the cholinergic and antioxidant defense systems.

Degradation of lignin β-aryl ether units in Arabidopsis thaliana expressing LigD, LigF and LigG from Sphingomonas paucimobilis SYK-6

Lignin is a major polymer in the secondary plant cell wall and composed of hydrophobic interlinked hydroxyphenylpropanoid units. The presence of lignin hampers conversion of plant biomass into biofuels; plants with modified lignin are therefore being investigated for increased digestibility. The bacterium Sphingomonas paucimobilis produces lignin-degrading enzymes including LigD, LigF and LigG involved in cleaving the most abundant lignin interunit linkage, the β-aryl ether bond. In this study, we expressed the LigD, LigF and LigG (LigDFG) genes in Arabidopsis thaliana to introduce postlignification modifications into the lignin structure. The three enzymes were targeted to the secretory pathway. Phenolic metabolite profiling and 2D HSQC NMR of the transgenic lines showed an increase in oxidized guaiacyl and syringyl units without concomitant increase in oxidized β-aryl ether units, showing lignin bond cleavage. Saccharification yield increased significantly in transgenic lines expressing LigDFG, showing the applicability of our approach. Additional new information on substrate specificity of the LigDFG enzymes is also provided.

Extra-Cellular But Extra-Ordinarily Important for Cells: Apoplastic Reactive Oxygen Species Metabolism

Reactive oxygen species (ROS), by their very nature, are highly reactive, and it is no surprise that they can cause damage to organic molecules. In cells, ROS are produced as byproducts of many metabolic reactions, but plants are prepared for this ROS output. Even though extracellular ROS generation constitutes only a minor part of a cell's total ROS level, this fraction is of extraordinary importance. In an active apoplastic ROS burst, it is mainly the respiratory burst oxidases and peroxidases that are engaged, and defects of these enzymes can affect plant development and stress responses. It must be highlighted that there are also other less well-known enzymatic or non-enzymatic ROS sources. There is a need for ROS detoxification in the apoplast, and almost all cellular antioxidants are present in this space, but the activity of antioxidant enzymes and the concentration of low-mass antioxidants is very low. The low antioxidant efficiency in the apoplast allows ROS to accumulate easily, which is a condition for ROS signaling. Therefore, the apoplastic ROS/antioxidant homeostasis is actively engaged in the reception and reaction to many biotic and abiotic stresses.

Drought Induced Changes in Growth, Osmolyte Accumulation and Antioxidant Metabolism of Three Maize Hybrids

Consequences of drought stress in crop production systems are perhaps more deleterious than other abiotic stresses under changing climatic scenarios. Regulations of physio-biochemical responses of plants under drought stress can be used as markers for drought stress tolerance in selection and breeding. The present study was conducted to appraise the performance of three different maize hybrids (Dong Dan 80, Wan Dan 13, and Run Nong 35) under well-watered, low, moderate and SD conditions maintained at 100, 80, 60, and 40% of field capacity, respectively. Compared with well-watered conditions, drought stress caused oxidative stress by excessive production of reactive oxygen species (ROS) which led to reduced growth and yield formation in all maize hybrids; nevertheless, negative effects of drought stress were more prominent in Run Nong 35. Drought-induced osmolyte accumulation and strong enzymatic and non-enzymatic defense systems prevented the severe damage in Dong Dan 80. Overall performance of all maize hybrids under drought stress was recorded as: Dong Dan 80 > Wan Dan 13 > Run Nong 35 with 6.39, 7.35, and 16.55% yield reductions. Consequently, these biochemical traits and differential physiological responses might be helpful to develop drought tolerance genotypes that can withstand water-deficit conditions with minimum yield losses.

Exogenous IAA differentially affects growth, oxidative stress and antioxidants system in Cd stressed Trigonella foenum-graecum L. seedlings: Toxicity alleviation by up-regulation of ascorbate-glutathione cycle

In the present study, effect of exogenous indole-3-acetic acid at their different levels (i.e. low; IAAL, 10µM and high; IAAH, 100µM) were studied on growth, oxidative stress biomarkers and antioxidant enzymes (SOD, POD, CAT and GST), and metabolites (AsA and GSH) as well as enzymes (APX, GR and DHAR) of ascorbate-glutathione cycle in Trigonella foenum-graecum L. seedlings grown under cadmium (Cd1, 3mgCd kg(-1) soil and Cd2, 9mgCd kg(-1) soil) stress. Cadmium (Cd) at both doses caused reduction in growth which was correlated with enhanced lipid peroxidation and damage to membrane as a result of excess accumulation of O2(•-) and H2O2. Cd also enhanced the oxidation of AsA and GSH to DHA and GSSG, respectively which give a clear sign of oxidative stress, despite of accelerated activity of enzymatic antioxidants: SOD, CAT, POD, GST as well as APX, DHAR (except in Cd2 stress) and GR. Exogenous application of IAAL resulted further rise in the activities of these enzymes, and maintained the redox status (> ratios: AsA/DHA and GSH/GSSG) of cells. The maintained redox status of cells under IAAL treatment declined the level of ROS in Cd1 and Cd2 treated seedlings thereby alleviated the Cd toxicity and this effect was more pronounced under Cd1 stress. Contrary to this, exogenous IAAH suppressed the activity of DHAR and GR and disturbed the redox status (< ratios: AsA/DHA and GSH/GSSG) of cells, hence excess accumulation of ROS further aggravated the Cd induced damage. Thus, overall results suggest that IAA at low (IAAL) and high (IAAH) doses affected the Cd toxicity differently by regulating the ascorbate-glutathione cycle as well as activity of other antioxidants in Trigonella seedlings.

Cadmium-Induced Hydrogen Accumulation Is Involved in Cadmium Tolerance in Brassica campestris by Reestablishment of Reduced Glutathione Homeostasis

Hydrogen gas (H2) was recently proposed as a therapeutic antioxidant and signaling molecule in clinical trials. However, the underlying physiological roles of H2 in plants remain unclear. In the present study, hydrogen-rich water (HRW) was used to characterize the physiological roles of H2 in enhancing the tolerance of Brassica campestris against cadmium (Cd). The results showed that both 50 μM CdCl2 and 50%-saturated HRW induced an increase of endogenous H2 in Brassica campestris seedlings, and HRW alleviated Cd toxicity related to growth inhibition and oxidative damage. Seedlings supplied with HRW exhibited increased root length and reduced lipid peroxidation, similar to plants receiving GSH post-treatment. Additionally, seedlings post-treated with HRW accumulated higher levels of reduced glutathione (GSH) and ascorbic acid (AsA) and showed increased GST and GPX activities in roots. Molecular evidence illustrated that the expression of genes such as GS, GR1 and GR2, which were down-regulated following the addition of Cd, GSH or BSO, could be reversed to varying degrees by the addition of HRW. Based on these results, it could be proposed that H2 might be an important regulator for enhancing the tolerance of Brassica campestris seedlings against Cd, mainly by governing reduced glutathione homeostasis.

High-Throughput Sequencing Identifies Novel and Conserved Cucumber (Cucumis sativus L.) microRNAs in Response to Cucumber Green Mottle Mosaic Virus Infection

Seedlings of Cucumis sativus L. (cv. 'Zhongnong 16') were artificially inoculated with Cucumber green mottle mosaic virus (CGMMV) at the three-true-leaf stage. Leaf and flower samples were collected at different time points post-inoculation (10, 30 and 50 d), and processed by high throughput sequencing analysis to identify candidate miRNA sequences. Bioinformatic analysis using screening criteria, and secondary structure prediction, indicated that 8 novel and 23 known miRNAs (including 15 miRNAs described for the first time in vivo) were produced by cucumber plants in response to CGMMV infection. Moreover, gene expression profiles (p-value <0.01) validated the expression of 3 of the novel miRNAs and 3 of the putative candidate miRNAs and identified a further 82 conserved miRNAs in CGMMV-infected cucumbers. Gene ontology (GO) analysis revealed that the predicted target genes of these 88 miRNAs, which were screened using the psRNATarget and miRanda algorithms, were involved in three functional categories: 2265 in molecular function, 1362 as cellular components and 276 in biological process. The subsequent Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that the predicted target genes were frequently involved in metabolic processes (166 pathways) and genetic information processes (40 pathways) and to a lesser degree the biosynthesis of secondary metabolites (12 pathways). These results could provide useful clues to help elucidate host-pathogen interactions in CGMMV and cucumber, as well as for the screening of resistance genes.

Biomarkers of ecotoxicological oxidative stress in an urban environment: using evergreen plant in industrial areas

Plants react to air pollution by increased production of reactive oxygene species and oxidative stress, which triggers multiple defense mechanisms. In this study, some parameters that serve as biomarkers for antioxidative defense, such as glutathione S-transferase (GST) activity, glutathione (GSH), malondialdehyde, chlorophyll and total soluble protein contents, were investigated on the needles of Cedrus libani (A. Rich.) grown around two industrial areas in Eskisehir. The measurements revealed that metabolism in needles of C. libani trees is largely directed towards defence against ROS, due to effects of air pollution in the sampling areas. We observed significant increases in all parameters, except chlorophyll contents, which were strongly decreased. However, these sharp changes were also prominent not only between sampling sites and control site, but also among the areas investigated, suggesting the quantitative influence of the extent of pollution. Together with total soluble protein contents, the correlation between GST activities and GSH contents suggests that damage due to oxidative stress was most probably reduced due to the increased antioxidant capacity. Therefore, we can suggest C. libani as a good model for biomonitoring atmospheric quality with the oxidative stress parameters providing an effective measure for early environmental assessment due to their sensitivities of even low levels of pollution.

Gene knockout of glutathione reductase 3 results in increased sensitivity to salt stress in rice

Glutathione reductase (GR) is one of important antioxidant enzymes in plants. This enzyme catalyzes the reduction of glutathione disulfide (GSSG) to reduced glutathione (GSH) with the accompanying oxidation of NADPH. Previously, we showed that salt-stress-responsive GR3 is a functional protein localized in chloroplasts and mitochondria in rice. To learn more about the role of GR3 in salt-stress tolerance, we investigated the response to 100 mM NaCl treatment in wild-type rice (WT); GR3 knockout mutant of rice (gr3); and the functional gr3-complementation line (C1). Rice GR3 was primarily expressed in roots at the seedling stage and ubiquitously expressed in all tissues except the sheath at heading stage. GR3 promoter-GUS was expressed in the vascular cylinder and cortex of root tissues in rice seedlings, vascular tissue of nodes, embryo and aleurone layer of seeds, and young flowers. Under both normal and salt-stress conditions, total GR activity was decreased by 20 % in gr3. Oxidative stress, indicated by malondialdehyde content, was greater in gr3 than the WT under salt stress. As compared with the WT, gr3 was sensitive to salt and methyl viologen; it showed inhibited growth, decreased maximal efficiency of photosystem II, decreased GSH and GSSG contents, and the ratio of GSH to GSSG. Conversely, the gr3-complementation line C1 rescued the tolerance to methyl viologen and salinity and recovered the growth and physiological damage caused by salinity. These results reveal that GR3 plays an important role in salt stress tolerance by regulating the GSH redox state in rice.

Physical and chemical indices of cucumber seedling leaves under dibutyl phthalate stress

Phthalic acid ester (PAE) pollution to soil can lead to phytotoxicity in plants and potential health risks to human being. Dibutyl phthalate (DBP) as a kind of PAE has a large usage amount and large residues in soil. To analyze antioxidant responses of plants to DBP stress, effects of varying DBP concentrations on cucumber seedlings growth had been investigated. Malonaldehyde (MDA), hydrogen peroxide (H2O2), chlorophyll, proline, glutathione (GSH), and oxidized glutathione (GSSH) contents and activities of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and peroxidase (POD) were studied. The results showed that H2O2 content increased in cucumber seedlings with the increase of DBP concentration. The chlorophyll content in the higher DBP significantly declined compared to the control. In the present study, a disturbance of the GSH redox balance was evidenced by a marked decrease in GSH/GSSG ratio in cucumber seedlings subjected DBP stress. Our results indicated that DBP treatment not only inhibited antioxidant capacity and antioxidant enzyme activity in seedlings' leaves but might also induce chlorophyll degradation or reduce the synthesis of chlorophyll. Moreover, it could also enhance the accumulation of reactive oxygen species (ROS) which induced membrane lipid peroxidation. DBP also altered the ultrastructure of mesophyll cells, damaged membrane structure of chloroplast and mitochondrion, and increased the number and size of starch grains in chloroplasts reducing the photosynthetic capacity.

Compartment-specific importance of glutathione during abiotic and biotic stress

The tripeptide thiol glutathione (γ-L-glutamyl-L-cysteinyl-glycine) is the most important sulfur containing antioxidant in plants and essential for plant defense against abiotic and biotic stress conditions. It is involved in the detoxification of reactive oxygen species (ROS), redox signaling, the modulation of defense gene expression, and the regulation of enzymatic activities. Even though changes in glutathione contents are well documented in plants and its roles in plant defense are well established, still too little is known about its compartment-specific importance during abiotic and biotic stress conditions. Due to technical advances in the visualization of glutathione and the redox state through microscopical methods some progress was made in the last few years in studying the importance of subcellular glutathione contents during stress conditions in plants. This review summarizes the data available on compartment-specific importance of glutathione in the protection against abiotic and biotic stress conditions such as high light stress, exposure to cadmium, drought, and pathogen attack (Pseudomonas, Botrytis, tobacco mosaic virus). The data will be discussed in connection with the subcellular accumulation of ROS during these conditions and glutathione synthesis which are both highly compartment specific (e.g., glutathione synthesis takes place in chloroplasts and the cytosol). Thus this review will reveal the compartment-specific importance of glutathione during abiotic and biotic stress conditions.

Exogenous 5-aminolevulenic acid promotes seed germination in Elymus nutans against oxidative damage induced by cold stress

The protective effects of 5-aminolevulenic acid (ALA) on germination of Elymus nutans Griseb. seeds under cold stress were investigated. Seeds of E. nutans (Damxung, DX and Zhengdao, ZD) were pre-soaked with various concentrations (0, 0.1, 0.5, 1, 5, 10 and 25 mg l⁻¹) of ALA for 24 h before germination under cold stress (5°C). Seeds of ZD were more susceptible to cold stress than DX seeds. Both seeds treated with ALA at low concentrations (0.1–1 mg l⁻¹) had higher final germination percentage (FGP) and dry weight at 5°C than non-ALA-treated seeds, whereas exposure to higher ALA concentrations (5–25 mg l⁻¹) brought about a dose dependent decrease. The highest FGP and dry weight of germinating seeds were obtained from seeds pre-soaked with 1 mg l⁻¹ ALA. After 5 d of cold stress, pretreatment with ALA provided significant protection against cold stress in the germinating seeds, significantly enhancing seed respiration rate and ATP synthesis. ALA pre-treatment also increased reduced glutathione (GSH), ascorbic acid (AsA), total glutathione, and total ascorbate concentrations, and the activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR), whereas decreased the contents of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂), and superoxide radical (O₂^•−) release in both germinating seeds under cold stress. In addition, application of ALA increased H⁺-ATPase activity and endogenous ALA concentration compared with cold stress alone. Results indicate that ALA considered as an endogenous plant growth regulator could effectively protect E. nutans seeds from cold-induced oxidative damage during germination without any adverse effect.