Plant Antioxidant System Research Articles

Effect of Exogenous NO on the Plant Growth and Antioxidant System of Eggplant Seedlings under High Temperature Stress

Effect of Exogenous NO on the Plant Growth and Antioxidant System of Eggplant Seedlings under High Temperature Stress

Evaluation of expression changes, proteins interaction network, and microRNAs targeting catalase and superoxide dismutase genes under cold stress in rapeseed (Brassica napus L.)

Rapeseed is the third-largest source of plant oil and one of the essential oil plants worldwide. Cold stress is one of the critical factors that affect plant yield. Therefore, improving cold stress tolerance is necessary for yield increase. The present study investigated BnCAT1 and BnCSD1 genes’ expression behavior in a tolerant and sensitive cultivar under cold stress (4 °C). Besides, protein-protein interaction networks of CATs and CSDs enzymes, and their association with other antioxidant enzymes were analyzed. Moreover, the microRNAs targeting BnCAT1 and BnCSD1 genes were predicted. This study indicated many direct and indirect interactions and the association between the components of the plant antioxidant system. However, not only did the CATs and CSDs enzymes have a relationship with each other, but they also interacted directly with ascorbate peroxidase and glutathione reductase enzymes. Also, 23 and 35 effective microRNAs were predicted for BnCAT1 and BnCSD1 genes, respectively. The gene expression results indicated an elevated expression of BnCAT1 and BnCSD1 in both tolerant and sensitive cultivars. However, this increase was more noticeable in the tolerant cultivar. Thus, the BnCSD1 gene had the highest expression in the early hour of cold stress, especially in the 12th h, and the BnCAT1 gene showed the highest expression in the 48th h. This result may indicate a functional relationship between these enzymes.

Study of Superoxide Dismutase Activity in Long-Term Cultivated Artemisia and Althaea "hairy" Roots.

The aim of the study was to evaluate the long-term effect of Agrobacterium rhizogenes genes transfer on plant antioxidant system by the study of superoxide dismutase (SOD) activity in "hairy" roots of Artemisia and Althaeaspp plants. PCR analyses revealed stability of the transformation and presence of bacterial rolB and rolC genes in the "hairy" roots after 4-6years from the transformation event. SOD activity in the roots of untransformed in vitro cultivated plants used for the initiation of "hairy" roots growth was in the range of 45.8 ± 8.7 U/μg (Althaea officinalis) and 275 ± 97.1 U/μg (Artemisia ludoviciana). After a long-term in vitro cultivation more than half of tested "hairy" root lines (54%) showed a significant increase in SOD activity values compared to untransformed roots. The highest SOD activity values of "hairy" root lines (24-fold increase) were founded in A.officinalis (1105 ± 174 U/μg) and A.dracunculus (1356 ± 402 U/μg). The increase of the activity was found also in "hairy" roots of A.vulgaris (up to 375 ± 28.2 U/μg, sevenfold increase), A.ludoviciana (1001 ± 191 U/μg, 3.6-fold increase), and A.tilesii (438 ± 104 U/μg, 1.6-fold increase). The results of our study indicate that transformation by wild-type A.rhizogenes not harboring any foreign genes implementing in SOD activity regulation can often stably activate plant antioxidant enzyme system. This effect, observed in the "hairy" roots of five plant species in 4-6years of the transformation event, obviously, should be taken into account in works aimed at creating transgenic plants by Agrobacterium-mediated transformation.

Microplastic residues in wetland ecosystems: Do they truly threaten the plant-microbe-soil system?

The ecological stress of microplastic contamination to ecosystem functioning and biota raises concerns worldwide, but the impacts of microplastics on wetland ecosystems (e.g., plants, microbes, and soil) have not been fully elucidated. In this study, we used a controlled pot experiment to determine the effects of different types (PS, PVC, PP and PE) of microplastics on the growth performance of wetland plants, soil chemical properties, enzyme systems and microbial communities. Microplastics can change the germination strategies of seeds, and there was also a reduction in fresh weight and plant height in Bacopa sp. Chlorophyllb synthesiswas significantly reduced in mixed microplastic treatments compared with controls. Microplastic addition in soil caused higher concentrations of reactive oxygen species in plants, which led to increased lipid peroxidation and activation of the antioxidant defence system. The organic matter, potassium, total nitrogen and phosphorus changed significantly in the presence of the four forms of microplastics, while soil pH was not substantially affected. Microplastics had a negative effect on soil enzyme activity, for example, PS MP particles significantly decreased sucrase activities in the soil after 40days. The results of this study showed that microplastic addition decreased the richness and diversity of bacterial. When soil was exposed to polystyrene microplastics, the richness and diversity of algae significantly increased on the soil surface. Thus, microplastics can alters the structure of soil microbial communities, resulting in the enrichment of some special soil microbial taxa involved in nitrogen cycling. These results indicate both the direct and indirect effects of plastic residues on the plant-microbe-soil system, which has implications for potential further impacts on wetland ecosystem functioning.

Nanoparticles as Potential Improvement for Conventional Fertilisation in the Cultivation of Raphanus sativus var. sativus

The use of nanoparticles in fertilisation has confirmed positive effects on plant growth and yield. Simultaneously, there is still little research into the effects of nanoparticles on the antioxidant system of plants. Due to the positive effect of nano zinc oxide on plants and the special property of nano zero-valent iron, these particles were selected for the research. The nano zero-valent iron is crucial for plants as it is present in agglomerations on the surface of roots where it increases the absorptive surface of the rhizosphere and causes elongation of the roots. The study aims to determine the influence of selected nanoparticles as a potential improvement for conventional fertilisation by magnesium (Mg), calcium (Ca), phosphorus (P) and nitrogen (N). After the cultivation, the influence of nanoparticles on the accumulation of macronutrients in plant tissues, biometric parameters, and physiological response (chlorophyll and antioxidant system) of radish (Raphanus sativus) were assessed. The solution used in this study helped to increase the content of nitrates (V) in radish roots by 31.7–73.2% compared to conventional fertilisation. Nevertheless, nanoparticles supplementation resulted in a decrease in the concentrations of magnesium, iron (Fe) and zinc (Zn) in plants. The high dose of used fertilisers increased the thickness and length of tubers by approximately 50.0%, compared to the control samples. The “Macro 2 + nano” variant caused an increase of plant biomass up to 70.0%. The analysis of the antioxidant system showed that the application of macronutrients with nanoparticles increased the concentration of polyphenols in plant tubers by 46.0–55.6%. Interestingly, while implemented conditions caused a 1.5-fold increase in CAT activity in leaves, at the same time the decrease in CAT activity in plant roots was observed. Based on the obtained results of the enzymatic antioxidant system and biometric parameters of plants, it can be concluded that (in laboratory conditions) nZVI and nanoZnO are efficient components of fertilisers. However, the effects on other organisms must be investigated before implementing a method for widespread use.

Plant Growth-Promoting Rhizobacteria as a Green Alternative for Sustainable Agriculture

Environmental stress is a major challenge for sustainable food production as it reduces yield by generating reactive oxygen species (ROS) which pose a threat to cell organelles and biomolecules such as proteins, DNA, enzymes, and others, leading to apoptosis. Plant growth-promoting rhizobacteria (PGPR) offers an eco-friendly and green alternative to synthetic agrochemicals and conventional agricultural practices in accomplishing sustainable agriculture by boosting growth and stress tolerance in plants. PGPR inhabit the rhizosphere of soil and exhibit positive interaction with plant roots. These organisms render multifaceted benefits to plants by several mechanisms such as the release of phytohormones, nitrogen fixation, solubilization of mineral phosphates, siderophore production for iron sequestration, protection against various pathogens, and stress. PGPR has the potential to curb the adverse effects of various stresses such as salinity, drought, heavy metals, floods, and other stresses on plants by inducing the production of antioxidant enzymes such as catalase, peroxidase, and superoxide dismutase. Genetically engineered PGPR strains play significant roles to alleviate the abiotic stress to improve crop productivity. Thus, the present review will focus on the impact of PGPR on stress resistance, plant growth promotion, and induction of antioxidant systems in plants.

Cr (VI)-induced oxidative damage impairs ammonia assimilation into organic forms in Solanum lycopersicum L.

Chromium (Cr) is a dangerous metal that has been found in the environment in high amounts as the result of numerous human activities, with proven negative effects on various organisms, including plants. The exposure of some plant species to this metal resulted in reduced growth, impaired nutrient uptake, and led to an overproduction of reactive oxygen species (ROS), ultimately causing oxidative damage. Nevertheless, studies regarding the impact of Cr on nitrogen (N) metabolism, the main limiting factor for plant growth, either directly or through the occurrence of oxidative stress, are scarce. Thus, this work aimed to explore the interplay between ammonia (NH4+) assimilation, redox homeostasis and antioxidant (AOX) system of tomato plants exposed to increased concentrations of Cr (VI) (0, 5 and 10 µM). The results revealed that Cr (VI) induced biometric damages, with roots being the most affected organ. Glutamine synthetase (GS) was differentially influenced by the metal at the gene expression, protein and activity levels, whereas glutamate dehydrogenase (GDH) activity was enhanced. Moreover, in Cr (VI)-treated plants, the observed oxidative damage was dependent on metal concentration and plant organ, with a differential accumulation of ROS and a generalized increase of lipid peroxidation (LP) recorded, being paired with an overall failure of the enzymatic antioxidant (AOX) system. Still, the non-enzymatic AOX component had a relevant role in the protection of plants against Cr (VI). Overall, the obtained results suggest that Cr (VI)-mediated plant growth reduction resulted from the occurrence of oxidative stress, coupled with the lack of enzymatic AOX defense, which, consequently, affected the NH4+ assimilatory route.

Impact of biostimulant and saline water on cape gooseberry (Physalis peruviana L.) in Brazil.

Production of Physalis peruviana L. has gained prominence in Northeastern Brazil. However, salinity limits the crop development in the Brazilian semiarid. Thus, this research aimed to evaluate the application of Acadian® biostimulant as mitigant of the deleterious effects of salinity on growth and gas exchange of P. peruviana plants. The experiment was combining different electrical conductivity of irrigation water (0.50, 1.23, 3.00, 4.44, and 5.50 dS m-1) and biostimulant doses (0.00, 1.45, 5.00, 8.55, and 10.00mL L-1). The main variables evaluated were plant height, stem diameter, number of leaves, root length, leaf area, specific leaf area, leaf area ratio, absolute and relative growth rate for plant height, and gas exchange. Experimental results showed that an increase in electrical conductivity of irrigation water had negatively affected the growth components and gas exchange in P. peruviana. Also, the application of seaweed-based biostimulant improves the photosynthetic capacity (43.3%), reduces transpiration rate (26.5%) and water loss by this process, further it attenuated the deleterious effects of salinity on specific leaf area, leaf area ratio, and stomatal conductance. To further elucidate the effectiveness of biostimulant application as a mitigant of salt stress, research aimed at the biochemical and enzyme activities of the plant's antioxidant system should be conducted to better understand this process.

Foliar melatonin stimulates cotton boll distribution characteristics by modifying leaf sugar metabolism and antioxidant activities during drought conditions.

Drought is a severe abiotic stress affecting the plant's antioxidant system and interrupting compatible solute translocation processes, which leads to low productivity. Melatonin acts as a common growth regulator enhancing the plants defense system and regulates sugar metabolism in challenging environments. Melatonin treatments enable plants to be tolerant to abiotic stresses via enhancing their recovery potential, but its impact using various concentrations has not yet been studied in leaf physiological aspects when applied to cotton foliage during their peak flowering and boll loading stage. The overall objective of this research was to facilitate cotton boll distribution characteristics by modifying cotton leaf sugar metabolism and antioxidant activity by applying foliar melatonin (0, 25, 50, and 100 μmol l-1 ) under drought levels with a relative soil water content of 75%, 60%, and 45% ± 5 (FC1, FC2, and FC3, respectively). Higher rates of melatonin application (100 μmol l-1 ) enhanced boll distribution characteristics and controlled the boll shedding rate during drought conditions. An increase in melatonin rates proved to be more helpful in stimulating cotton sympodial leaf physiological attributes, including leaf gas exchange parameters, sugar metabolism, proline content, and antioxidants defense system as compared with less or no melatonin application during all FC conditions and showed the most significant effect at a higher melatonin concentration (M100) at 7-21 DAF. The total proline content and antioxidant activity were enhanced in the M100 treatment during all FC levels, which caused a reduction in the total malondialdehyde (MDA) contents and hydrogen peroxide (H2 O2 ) concentrations in cotton leaves. Moreover, sugar metabolism responsible genes GhSusA and SPS2 showed an upsurge in expression levels and enhanced sucrose degradation in M100 treatments during all FC levels. Furthermore, cotton boll attributes showed also a positive relation with leaf physiological and gas exchange attributes. The results suggested that foliar melatonin application during the flowering initiation stage improved the overall performance and is helpful for cotton crops productivity against drought stress.

Priming of Plant Defenses against Ophiostoma novo-ulmi by Elm (Ulmus minor Mill.) Fungal Endophytes.

Some fungal endophytes of forest trees are recognized as beneficial symbionts against stresses. In previous works, two elm endophytes from the classes Cystobasidiomycetes and Eurotiomycetes promoted host resistance to abiotic stress, and another elm endophyte from Dothideomycetes enhanced host resistance to Dutch elm disease (DED). Here, we hypothesize that the combined effect of these endophytes activate the plant immune and/or antioxidant system, leading to a defense priming and/or increased oxidative protection when exposed to the DED pathogen Ophiostoma novo-ulmi. To test this hypothesis, the short-term defense gene activation and antioxidant response were evaluated in DED-susceptible (MDV1) and DED-resistant (VAD2 and MDV2.3) Ulmus minor genotypes inoculated with O. novo-ulmi, as well as two weeks earlier with a mixture of the above-mentioned endophytes. Endophyte inoculation induced a generalized transient defense activation mediated primarily by salicylic acid (SA). Subsequent pathogen inoculation resulted in a primed defense response of variable intensity among genotypes. Genotypes MDV1 and VAD2 displayed a defense priming driven by SA, jasmonic acid (JA), and ethylene (ET), causing a reduced pathogen spread in MDV1. Meanwhile, the genotype MDV2.3 showed lower defense priming but a stronger and earlier antioxidant response. The defense priming stimulated by elm fungal endophytes broadens our current knowledge of the ecological functions of endophytic fungi in forest trees and opens new prospects for their use in the biocontrol of plant diseases.

The role of antioxidants in the mechanisms of adaptation of <i>Poa Pratensis </i>L. under the influence of wooden plants

The article analyzes the results on the content of peroxidase, phenolic compounds and ascorbic acid in the leaves of meadow bluegrass during the growing season under plantations of woody plants (scots pine and ash-leaved maple). The peroxidase activity in the leaves of plant samples was determined by the method of A.N. Boyarkin, the content of ascorbic acid - by the titrimetric method using sodium 2,6-dichlorophenolindophenol, water-soluble phenolic compounds - by the Leventhal-Neubauer method. Mutual regulation of the plant antioxidant defense system was established, expressed in an increase in the level of ascorbic acid, but a decrease in the activity of peroxidase and phenolic compounds. The accumulation of metabolites in the studied plants varied depending on the phases of the growing season and growing conditions. Scots pine had the greatest inhibitory effect on the studied species than ash-leaved maple. The results obtained can be used to assess the state of the ground cover and the structure of the phytocenosis.

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

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

Genome-Wide Analysis and Expression Profile of Superoxide Dismutase (SOD) Gene Family in Rapeseed (Brassica napus L.) under Different Hormones and Abiotic Stress Conditions.

Superoxide dismutase (SOD) is an important enzyme that acts as the first line of protection in the plant antioxidant defense system, involved in eliminating reactive oxygen species (ROS) under harsh environmental conditions. Nevertheless, the SOD gene family was yet to be reported in rapeseed (Brassica napus L.). Thus, a genome-wide investigation was carried out to identify the rapeseed SOD genes. The present study recognized 31 BnSOD genes in the rapeseed genome, including 14 BnCSDs, 11 BnFSDs, and six BnMSDs. Phylogenetic analysis revealed that SOD genes from rapeseed and other closely related plant species were clustered into three groups based on the binding domain with high bootstrap values. The systemic analysis exposed that BnSODs experienced segmental duplications. Gene structure and motif analysis specified that most of the BnSOD genes displayed a relatively well-maintained exon–intron and motif configuration within the same group. Moreover, we identified five hormones and four stress- and several light-responsive cis-elements in the promoters of BnSODs. Thirty putative bna-miRNAs from seven families were also predicted, targeting 13 BnSODs. Gene ontology annotation outcomes confirm the BnSODs role under different stress stimuli, cellular oxidant detoxification processes, metal ion binding activities, SOD activity, and different cellular components. Twelve BnSOD genes exhibited higher expression profiles in numerous developmental tissues, i.e., root, leaf, stem, and silique. The qRT-PCR based expression profiling showed that eight genes (BnCSD1, BnCSD3, BnCSD14, BnFSD4, BnFSD5, BnFSD6, BnMSD2, and BnMSD10) were significantly up-regulated under different hormones (ABA, GA, IAA, and KT) and abiotic stress (salinity, cold, waterlogging, and drought) treatments. The predicted 3D structures discovered comparable conserved BnSOD protein structures. In short, our findings deliver a foundation for additional functional investigations on the BnSOD genes in rapeseed breeding programs.

Barley stripe mosaic virus γb protein disrupts chloroplast antioxidant defenses to optimize viral replication.

The plant antioxidant system plays important roles in response to diverse abiotic and biotic stresses. However, the effects of virus infection on host redox homeostasis and how antioxidant defense pathway is manipulated by viruses remain poorly understood. We previously demonstrated that the Barley stripe mosaic virus (BSMV) γb protein is recruited to the chloroplast by the viral αa replicase to enhance viral replication. Here, we show that BSMV infection induces chloroplast oxidative stress. The versatile γb protein interacts directly with NADPH-dependent thioredoxin reductase C (NTRC), a core component of chloroplast antioxidant systems. Overexpression of NbNTRC significantly impairs BSMV replication in Nicotiana benthamiana plants, whereas disruption of NbNTRC expression leads to increased viral accumulation and infection severity. To counter NTRC-mediated defenses, BSMV employs the γb protein to competitively interfere with NbNTRC binding to 2-Cys Prx. Altogether, this study indicates that beyond acting as a helicase enhancer, γb also subverts NTRC-mediated chloroplast antioxidant defenses to create an oxidative microenvironment conducive to viral replication.

Arbuscular mycorrhizal fungi alleviate salinity stress in peanut: Evidence from pot‐grown and field experiments

AbstractArbuscular mycorrhizal fungi (AMF) species are essential for sustainable agriculture of legume crops; however, the AMF response in legume crops, especially from the perspective of physiological and molecular mechanisms under salinity conditions, is largely unknown. In this study, peanut (Arachis hypogaea L.) seeds were inoculated with AMF to investigate its salinity stress alleviation effects using the pot‐grown and 2‐year field experiments. Seeds from two peanut cultivars (HY22 and HY25) were inoculated with AMF Rhizophagus irregularis SA and Funneliformis mosseae BEG95 (1:1), and the physiological and transcriptional responses were compared between the AMF‐inoculated and non‐inoculated peanut plants. Under the salinity stress, compared with the control samples, the AMF‐inoculated plants showed higher net photosynthetic rate, leaf relative water content (RWC), plant height, osmolyte accumulation, but lower leaf relative electrolyte conductivity (REC). Also, the malondialdehyde (MDA) concentration was reduced while the antioxidant enzymes such as superoxide dismutase (SOD), guaiacol peroxidase (G‐POD), catalase (CAT), and ascorbate peroxidase (APX) were activated. Furthermore, transcriptome data revealed that AMF potentially alleviates salt stress by regulating redox processes, cell wall assembly, cell growth, and other similar processes. In the 2‐year field experiment, AMF‐inoculated peanut seeds of HY22 and HY25 were cultivated in both non‐saline and saline soils. Under salinity conditions, AMF inoculation induced the total protein concentration by 11.11 and 2.32% in kernels and further increased the peanut pod yield by 21.83 and 21.89% in HY22 and HY25, respectively. In non‐saline soil too, AMF increased the peanut pod yield by 11.47 and 23.98% in HY22 and HY25, respectively. Taken together, these results strongly demonstrate that the combination of AMF Rhizophagus irregularis SA and Funneliformis mosseae BEG95 (1:1) can alleviate salinity stress in peanuts by improving plant growth, photosystem, and antioxidant system. Additionally, it increases the peanut pod yield under both normal and salinity conditions.

Nigella sativa callus treated with sodium azide exhibit augmented antioxidant activity and DNA damage inhibition

Nigella sativa L. (NS) is an herbaceous plant, possessing phytochemicals of therapeutic importance. Thymoquinone is one of the active phytochemicals of NS that confers noteworthy antioxidant properties. Sodium azide, an agent of abiotic stress, can modulates antioxidant system in plants. In the present investigation, sodium azide (0, 5 µM, 10 µM, 20 µM, 50 µM, 100 µM and 200 µM) doses administered to the in vitro NS callus cultures for production/modification of secondary metabolites with augmented activity. 200 µM sodium azide treated NS callus exhibited maximum peroxidase activity (1.286 ± 0.101 nanokatal mg−1 protein) and polyphenol oxidase activity (1.590 ± 0.110 nanokatal mg−1 protein), while 100 µM sodium azide treated NS callus for optimum catalase activity (1.250 ± 0.105 nanokatal mg−1 protein). Further, 200 µM sodium azide treated NS callus obtained significantly the highest phenolics (3.666 ± 0.475 mg g−1 callus fresh weight), 20 µM sodium azide treated NS callus, the highest flavonoids (1.308 ± 0.082 mg g−1 callus fresh weight) and 100 µM sodium azide treated NS callus, the highest carotenes (1.273 ± 0.066 mg g−1 callus fresh weight). However, NS callus exhibited a decrease in thymoquinone yield/content vis-à-vis possible emergence of its analog with 5.3 min retention time and an increase in antioxidant property. Treatment with 200 µM sodium azide registered significantly the lowest percent yield of callus extract (4.6 ± 0.36 mg g−1 callus fresh weight) and thymoquinone yield (16.65 ± 2.52 µg g−1 callus fresh weight) and content (0.36 ± 0.07 mg g−1 callus dry weight) and the highest antioxidant activity (3.873 ± 0.402%), signifying a negative correlation of the former with the latter. DNA damage inhibition (24.3 ± 1.7%) was recorded significantly maximum at 200 µM sodium azide treatment. Sodium azide treated callus also recorded emergence of a new peak at 5.3 min retention time (possibly an analog of thymoquinone with augmented antioxidant activity) whose area exhibits significantly negative correlation with callus extract yield and thymoquinone yield/content and positive correlation with antioxidant activity and in vitro DNA damage inhibition. Thus, sodium azide treatment to NS callus confers possible production of secondary metabolites or thymoquinone analog (s) responsible for elevated antioxidant property and inhibition to DNA damage. The formation of potent antioxidants through sodium azide treatment to NS could be worthy for nutraceutical and pharmaceutical industries.

Exogenous melatonin induces drought stress tolerance by promoting plant growth and antioxidant defence system of soybean plants.

Melatonin is an indolamine bioactive molecule that regulates a wide range of physiological processes during plant growth and enhances abiotic stress tolerance. Here we examined the putative role of exogenous melatonin application (foliar or root zone) in improving drought stress tolerance in soybean seedlings. Pre-treatment of soybean seedlings with melatonin (50 and 100 µM) was found to significantly mitigate the negative effects of drought stress on plant growth-related parameters and chlorophyll content. The beneficial impacts against drought were more pronounced by melatonin application in the rhizosphere than in foliar treatments. The melatonin-induced enhanced tolerance could be attributed to improved photosynthetic activity, reduction of abscisic acid and drought-induced oxidative damage by lowering the accumulation of reactive oxygen species and malondialdehyde. Interestingly, the contents of jasmonic acid and salicylic acid were significantly higher following melatonin treatment in the root zone than in foliar treatment compared with the control. The activity of major antioxidant enzymes such as superoxide dismutase, catalase, polyphenol oxidase, peroxidase and ascorbate peroxidase was stimulated by melatonin application. In addition, melatonin counteracted the drought-induced increase in proline and sugar content. These findings revealed that modifying the endogenous plant hormone content and antioxidant enzymes by melatonin application improved drought tolerance in soybean seedlings. Our findings provide evidence for the stronger physiological role of melatonin in the root zone than in leaves, which may be useful in the large-scale field level application during drought.

Molecular Cloning and Functional Characterization of Heat Stress-Responsive Superoxide Dismutases in Garlic (Allium sativum L.).

Superoxide dismutases (SODs) are key antioxidant enzymes that can detoxify the superoxide radicals generated by various stresses. Although various plant SODs have been suggested to improve stress tolerance, SODs in garlic, an economically important vegetable grown worldwide, remain relatively unknown. In this study, we found that heat stress strongly induced the activities of Cu/ZnSODs, FeSODs, and MnSODs in garlic leaves. In addition, we cloned four garlic SODs (AsSODs) and suggest that heat stress-increased SOD activity was reflected at least by the induction of these AsSODs. The results of the agro-infiltration assay suggested that the cloned AsSODs encoded functional SOD enzymes belonging to the Cu/ZnSOD and MnSOD families. As a first step toward understanding the enzymatic antioxidant system in garlic plants, our results provide a solid foundation for an in-depth analysis of the physiological functions of the AsSOD family.

Analysis of the biodegradation and phytotoxicity mechanism of TNT, RDX, HMX in alfalfa (Medicago sativa)

The aim of this study was to reveal the mechanism underlying the toxicity of TNT (trinitrotoluene), RDX (cyclotrimethylene trinitroamine), and HMX (cyclotetramethylene tetranitramine) explosives pollution in plants. Here, the effects of exposure to these three explosives were examined on chlorophyll fluorescence, antioxidant enzyme activity, and the metabolite spectrum in alfalfa (Medicago sativa) plants. The degradation rates for TNT, RDX, and HMX by alfalfa were 26.8%, 20.4%, and 18.4%, respectively, under hydroponic conditions. TNT caused damage to the microstructure of the plant roots and inhibited photosynthesis, whereas RDX and HMX induced only minor changes. Exposure to any of the three explosives caused disturbances in the oxidase system. Non-targeted metabolomics identified a total of 6185 metabolites. TNT exposure induced the appearance of 609 differentially expressed metabolites (189 upregulated, 420 downregulated), RDX exposure induced 197 differentially expressed metabolites (155 upregulated and 42 downregulated), and HMX induced 234 differentially expressed metabolites (132 upregulated and 102 downregulated). Of these differentially expressed metabolites, lipids and lipid-like molecules were the main metabolites induced by explosives poisoning. TNT mainly caused significant changes in the alanine, aspartate, and glutamate metabolism metabolic pathways, RDX mainly caused disorders in the arginine biosynthesis metabolic pathway, and HMX disrupted the oxidative phosphorylation metabolic pathway. Taken together, the results show that exposure to TNT, RDX, and HMX leads to imbalances in plant photosynthetic characteristics and antioxidant enzyme systems, changes the basic metabolism of plants, and has significant ecotoxicity effects.

The potential of microbes and sulfate in reducing arsenic phytoaccumulation by maize (Zea mays L.) plants.

Arsenic (As) contamination in soil-plant system is an important environmental, agricultural and health issue globally. The microbe- and sulfate-mediated As cycling in soil-plant system may depend on soil sulfate levels, and it can be used as a potential strategy to reduce plant As uptake and improve plant growth. Here, we investigated the role of soil microbes (SMs) to examine As phytoaccumulation using maize as a test plant, under varying sulfate levels (S-0, S-5, S-25mmolkg-1) and As stress. The addition of sulfate and SMs promoted maize plant growth and reduced As concentration in shoots compared to sulfate-treated plants without SMs. Results revealed that theSMs-S-5 treatment proved to be the most promising in reducing As uptake by 27% and 48% in root and shoot of the maize plants, respectively. The SMs-S treatments, primarily with S-5, enhanced plant growth, shoot dry biomass, Chl a, b and total Chl (a + b) contents, and gas exchange attributes of maize plants. Similarly, the antioxidant defense in maize plants was increased significantly in SMs-S-treated plants, notably with SMs-S-5 treatment. Overall, the SMs-S-5-treated plants possessed improved plant growth, dry biomass, physiology and antioxidant defense system and decrease in plant shoot As concentration. The outcomes of this study suggest that sulfate supplementation in soil along with SMs could assist in reducing As accumulation by maize plants, thus providing a sustainable and eco-friendly bioremediation strategy in limiting As exposure.