Micro and nanoplastics pollution: Sources, distribution, uptake in plants, toxicological effects, and innovative remediation strategies for environmental sustainability.

Microplastics and nanoplastics (MNPs), are minute particles resulting from plastic fragmentation, have raised concerns due to their widespread presence in the environment. This study investigates sources and distribution of MNPs and their impact on plants, elucidating the intricate mechanisms of toxicity. Through a comprehensive analysis, it reveals that these tiny plastic particles infiltrate plant tissues, disrupting vital physiological processes. Micro and nanoplastics impair root development, hinder water and nutrient uptake, photosynthesis, and induce oxidative stress and cyto-genotoxicity leading to stunted growth and diminished crop yields. Moreover, they interfere with plant-microbe interactions essential for nutrient cycling and soil health. The research also explores the translocation of these particles within plants, raising concerns about their potential entry into the food chain and subsequent human health risks. The study underscores the urgency of understanding MNPs toxicity on plants, emphasizing the need for innovative remediation strategies such as bioremediation by algae, fungi, bacteria, and plants and eco-friendly plastic alternatives. Addressing this issue is pivotal not only for environmental conservation but also for ensuring sustainable agriculture and global food security in the face of escalating plastic pollution.

Almond shell-derived biochar decreased toxic metals bioavailability and uptake by tomato and enhanced the antioxidant system and microbial community.

The effectiveness of almond shell-derived biochar (ASB) in immobilizing soil heavy metals (HMs) and its impact on soil microbial activity and diversity have not been sufficiently studied. Hence, a pot study was carried out to investigate the effectiveness of ASB addition at 2, 4, and 6 % (w/w) on soil biochemical characteristics and the bioavailability of Cd, Cu, Pb, and Zn to tomato (Solanum lycopersicum L.) plants, as compared to the control (contaminated soil without ASB addition). The addition of ASB promoted plant growth (up to two-fold) and restored the damage to the ultrastructure of chloroplast organelles. In addition, ASB mitigated the adverse effects of HMs toxicity by decreasing oxidative damage, regulating the antioxidant system, improving soil physicochemical properties, and enhancing enzymatic activities. At the phylum level, ASB addition enhanced the relative abundance of Actinobacteriota, Acidobacteriota, and Firmicutes while decreasing the relative abundance of Proteobacteria and Bacteroidota. Furthermore, ASB application increased the relative abundance of several fungal taxa (Ascomycota and Mortierellomycota) while reducing the relative abundance of Basidiomycota in the soil. The ASB-induced improvement in soil properties, microbial community, and diversity led to a significant decrease in the DTPA-extractable HMs down to 41.0 %, 51.0 %, 52.0 %, and 35.0 % for Cd, Cu, Pb, and Zn, respectively, as compared to the control. The highest doses of ASB (ASB6) significantly reduced the metals content by 26.0 % for Cd, 78.0 % for Cu, 38.0 % for Pb, and 20.0 % for Zn in the roots, and 72.0 % for Cd, 67.0 % for Cu, 46.0 % for Pb, and 35.0 % for Zn in the shoots, as compared to the control. The structural equation model predicts that soil pH and organic matter are driving factors in reducing the availability and uptake of HMs. ASB could be used as a sustainable trial for remediation of HMs polluted soils and reducing metal content in edible plants.

Synergistic influence of selenium and silicon supplementation prevents the oxidative effects of arsenic stress in wheat.

Influence of supplementation of selenium (Se, 1 and 5 µM) and silicon (Si, 0.1 and 0.5 mM) was investigated in wheat under arsenic (30 µM As) stress. Plants grown under As stress exhibited a significant decline in growth parameters however, Se and Si supplementation mitigated the decline significantly. Treatment of Se and Si alleviated the reduction in the intermediate components of chlorophyll biosynthesis pathway and the content of photosynthetic pigments. Arsenic stressed plants exhibited increased reactive oxygen species accumulation and the NADPH oxidase activity which were lowered significantly due to Se and Si treatments. Moreover, Se and Si supplementation reduced lipid peroxidation and activity of lipoxygenase and protease under As stress. Supplementation of Se and Si significantly improved the antioxidant activities and the content of cysteine, tocopherol, reduced glutathione and ascorbic acid. Treatment of Se and Si alleviated the reduction in nitrate reductase activity. Exogenously applied Se and Si mitigated the reduction in mineral elements and reduced As accumulation. Hence, supplementation of Se and Si is beneficial in preventing the alterations in growth and metabolism of wheat under As stress.

Alleviation of Adverse Effects of Drought Stress on Growth and Nitrogen Metabolism in Mungbean (Vigna radiata) by Sulphur and Nitric Oxide Involves Up-Regulation of Antioxidant and Osmolyte Metabolism and Gene Expression.

The influence of drought induced by polyethylene glycol (PEG) and the alleviatory effect of nitric oxide (50 µM) and sulphur (S, 1 mM K2SO4) were studied in Vigna radiata. Drought stress reduced plant height, dry weight, total chlorophylls, carotenoids and the content of nitrogen, phosphorous, potassium and sulphur. The foliar applications of NO and sulphur each individually alleviated the decline, with a greater alleviation observed in seedlings treated with both NO and sulphur. The reduction in intermediates of chlorophyll synthesis pathways and photosynthesis were alleviated by NO and sulphur. Oxidative stress was evident through the increased hydrogen peroxide, superoxide and activity of lipoxygenase and protease which were significantly assuaged by NO, sulphur and NO + sulphur treatments. A reduction in the activity of nitrate reductase, glutamine synthetase and glutamate synthase was mitigated due to the application of NO and the supplementation of sulphur. The endogenous concentration of NO and hydrogen sulphide (HS) was increased due to PEG; however, the PEG-induced increase in NO and HS was lowered due to NO and sulphur. Furthermore, NO and sulphur treatments to PEG-stressed seedlings further enhanced the functioning of the antioxidant system, osmolytes and secondary metabolite accumulation. Activities of γ-glutamyl kinase and phenylalanine ammonia lyase were up-regulated due to NO and S treatments. The treatment of NO and S regulated the expression of the Cu/ZnSOD, POD, CAT, RLP, HSP70 and LEA genes significantly under normal and drought stress. The present study advocates for the beneficial use of NO and sulphur in the mitigation of drought-induced alterations in the metabolism of Vigna radiata.

Corrigendum: Supplementation of nitric oxide and spermidine alleviates the nickel stress induced damage to growth, chlorophyll metabolism and photosynthesis by up-regulating ascorbate-glutathione and glyoxalase cycle functioning in tomato.

[This corrects the article DOI: 10.3389/fpls.2022.1039480.].

Different leafy vegetable cropping systems regulate growth, photosynthesis, and PSII functioning in mono-cropped eggplant by altering chemical properties and upregulating the antioxidant system.

Continuous cropping of eggplant threatened regional ecological sustainability by facilitating replanting problems under mono-cropping conditions. Therefore, alternative agronomic and management practices are required to improve crop productivity at low environmental cost for the development of sustainable agricultural systems in different regions. This study examined changes in soil chemical properties, eggplant photosynthesis, and antioxidant functioning in five different vegetable cropping systems over a 2-year period., 2017 and 2018. The results showed that welsh onion-eggplant (WOE), celery-eggplant (CE), non-heading Chinese cabbage-eggplant (NCCE), and leafy lettuce-eggplant (LLE) rotation systems significantly impacted growth, biomass accumulation, and yield than fallow-eggplant (FE). In addition, various leafy vegetable cropping systems, WOE, CE, NCCE, and LLT induced significant increases in soil organic matter (SOM), available nutrients (N, P, and K), and eggplant growth by affecting the photosynthesis and related gas exchange parameters with much evident effect due to CE and NCCE. Moreover, eggplant raised with different leafy vegetable rotation systems showed higher activity of antioxidant enzymes, resulting in lower accumulation of hydrogen peroxide and hence reduced oxidative damage to membranes. In addition, fresh and dry plant biomass was significantly increased due to crop rotation with leafy vegetables. Therefore, we concluded that leafy vegetable crop rotation is a beneficial management practice to improve the growth and yield of eggplant.

Differential activity of wheat antioxidant defense system and alterations in the accumulation of osmolytes at different developmental stages as influenced by marigold (Tagetes erecta L.) leachates.

Experiments were conducted to evaluate the effectivity of Tagetes erecta L. leachates on various growth, physiological, and biochemical parameters of wheat at different stages of growth. Results suggested that Triticum aestivum L. seedlings/plants when exposed to higher concentrations of marigold leachates (10%, 20%, and 30% w/v of fresh parts and 5% and 10% w/v of dry parts) exhibited enhanced lipid peroxidation along with an increase in the activity of protease and phenylalanine ammonia lyase. Treatment with higher concentrations of leachates of fresh (30% w/v) and dry (10% w/v) T. erecta upregulated the activity of superoxide dismutase, catalase, ascorbate peroxidase, guaiacol peroxidase, glutathione S-transferase, and glutathione reductase and also increased the non-enzymatic components of antioxidant defense such as glutathione, ascorbic acid, and total phenols along with osmotic constituents comprising free proline, free sugars, and free amino acids in wheat. The growth and yield attributes of wheat exhibited a slight increase at treatments with lower concentrations (1% w/v) of dry leachates, whereas a decrease was recorded at higher concentrations (10% w/v). In general, treatments with flower leachates (higher concentrations) showed greater influence as compared with those with leaf leachates. Identification and understanding the mechanism of function of allelochemicals in these leachates may pave a way for further experimentation on Tagetes erecta L crop while it is cultivated and decomposed in the field.

Supplementation of nitric oxide and spermidine alleviates the nickel stress-induced damage to growth, chlorophyll metabolism, and photosynthesis by upregulating ascorbate-glutathione and glyoxalase cycle functioning in tomato.

Experiments were conducted to evaluate the role of exogenously applied nitric oxide (NO; 50 µM) and spermidine (Spd; 100 µM) in alleviating the damaging effects of Ni (1 mM NiSO46H2O) toxicity on the growth, chlorophyll metabolism, photosynthesis, and mineral content in tomato. Ni treatment significantly reduced the plant height, dry mass, and the contents of glutamate 1-semialdehyde, δ-amino levulinic acid, prototoporphyrin IX, Mg-prototoporphyrin IX, total chlorophyll, and carotenoids; however, the application of NO and Spd alleviated the decline considerably. Supplementation of NO and Spd mitigated the Ni-induced decline in photosynthesis, gas exchange, and chlorophyll fluorescence parameters. Ni caused oxidative damage, while the application of NO, Spd, and NO+Spd significantly reduced the oxidative stress parameters under normal and Ni toxicity. The application of NO and Spd enhanced the function of the antioxidant system and upregulated the activity of glyoxalase enzymes, reflecting significant reduction of the oxidative effects and methylglyoxal accumulation. Tolerance against Ni was further strengthened by the accumulation of proline and glycine betaine due to NO and Spd application. The decrease in the uptake of essential mineral elements such as N, P, K, and Mg was alleviated by NO and Spd. Hence, individual and combined supplementation of NO and Spd effectively alleviates the damaging effects of Ni on tomato.

Regulatory hubs and strategies for improving heavy metal tolerance in plants: Chemical messengers, omics and genetic engineering.

Heavy metal (HM) accumulation in the agricultural soil and its toxicity is a major threat for plant growth and development. HMs disrupt functional integrity of the plants, induces altered phenological and physiological responses and slashes down qualitative crop yield. Chemical messengers such as phytohormones, plant growth regulators and gasotransmitters play a crucial role in regulating plant growth and development under metal toxicity in plants. Understanding the intricate network of these chemical messengers as well as interactions of genes/metabolites/proteins associated with HM toxicity in plants is necessary for deciphering insights into the regulatory circuit involved in HM tolerance. The present review describes (a) the role of chemical messengers in HM-induced toxicity mitigation, (b) possible crosstalk between phytohormones and other signaling cascades involved in plants HM tolerance and (c) the recent advancements in biotechnological interventions including genetic engineering, genome editing and omics approaches to provide a step ahead in making of improved plant against HM toxicities.

Improving growth and photosynthetic performance of drought stressed tomato by application of nano-organic fertilizer involves up-regulation of nitrogen, antioxidant and osmolyte metabolism.

Organic fertilizer usage is been introduced into agricultural practices for preventing the damaging effects of chemical fertilizers. Present study investigated the beneficial role of organic fertilizer (nano-vermicompost) on the growth, oxidative stress parameters, antioxidant and nitrogen metabolism, osmolyte accumulation and mineral elements in tomato under drought stress. Drought stress resulted in reduced growth and biomass accumulation by triggering oxidative stress due to excess accumulation of reactive oxygen species (ROS) and reduced mineral uptake. Application of nano-vermicompost proved significantly beneficial in improving growth and mitigating the drought induced growth decline. Nano-vermicompost increased growth and dry matter content and ameliorated the decline in chlorophyll contents, photosynthesis and PSII activity more significantly at higher concentration (100 mg kg-1 soil). ROS accumulation was significantly reduced by nano-vermicompost application thereby enhancing the membrane stability under normal as well as drought conditions. Furthermore, lipid peroxidation and activities of protease and lypoxygenase were significantly reduced. Drought up-regulated antioxidant system and application of nano-vermicompost further enhanced the activities of antioxidant enzymes and the contents of non-enzymatic antioxidant components. Accumulation of osmolytes including proline, glycine betaine and sugars increased significantly due to nano-vermicompost application. Besides, decline in the activity of nitrate reductase and content of essential mineral elements like nitrogen, potassium and phosphorous was also ameliorated by nano-vermicompost application.

Nitric oxide donor, sodium nitroprusside, mitigates mercury toxicity in different cultivars of soybean.

The present study reveals the effect of mercury (Hg) and sodium nitroprusside (SNP) on plant growth and metabolism in soybean cultivars (Pusa-24, Pusa-37and Pusa-40). Mercury stress decreased growth and biomass yield, and gas exchange attributes in all soybean cultivars. External supplementation of SNP mitigated Hg toxicity by improving growth and gas exchange parameters. Electrolyte leakage (EL) increased accompanied with elevated levels of malondialdehyde (MDA) and H2O2 under Hg stress, however, they were found to be reduced in all cultivars upon the exogenous application of SNP. The activities of anti-oxidative enzymes, superoxide dismutase and catalase (SOD and CAT) and those enzymes involved in the ascorbate-glutathione pathway were impaired by Hg stress, but they were regulated by the application of SNP. Accumulation of Hg and NO in the shoots and roots were also regulated by the application of NO. Although, all three cultivars were affected by Hg stress, Pusa-37 was relatively less affected. Mercury stress affected the growth and development of different soybean cultivars, but Pusa-37 being tolerant was less affected. Pusa-37 was found to be more responsive to SNP than Pusa-24, Pusa-40 under Hg toxicity. The external supplementation of SNP could be a sustainable approach to economically utilize Hg affected soils.

Comparative transcriptome analysis reveals the regulatory effects of acetylcholine on salt tolerance of Nicotiana benthamiana.

Salinity is a major cause of crop losses worldwide. Acetylcholine (ACh) can ameliorate the adverse effects of abiotic stresses on plant growth, including salinity stress; however, the underlying molecular mechanisms of this process are unclear. Here, seedlings of Nicotiana benthamiana grown under normal conditions or exposed to 150 mmol L-1 NaCl salinity stress were then treated with a root application of 10 µM ACh. Exogenous ACh application resulted in the downregulation of the activity of the antioxidant enzymes, ascorbate peroxidase, and catalase. ACh-treated plants had lower levels of reactive oxygen species, including the superoxide anion radical and hydrogen peroxide. Transcriptome analysis indicated that ACh treatment under salt stress promoted the differential expression of 658 genes in leaves of N. benthamiana (527 were upregulated and 131 were downregulated). Gene ontology enrichment and Kyoto Encyclopedia of Genes and Genomes pathway analyses revealed that exogenous ACh application was associated with a substantial increase in the transcripts of genes related to cell wall peroxidases, xyloglucan endotransglucosylases or hydrolases, and expansins, indicating that ACh activates cell wall biosynthesis in salt-stressed plants. ACh also enhanced the expression of genes associated with the auxin, gibberellin, brassinosteroid, and salicylic acid signalling pathways, indicating that ACh induces the activation of these pathways under salt stress. Collectively, these findings indicate that ACh-induced salt tolerance in N. benthamiana seedlings is mediated by the inhibition of antioxidant enzymes, activation of cell wall biosynthesis, and hormone signalling pathways. Stress-induced genes involved in osmotic regulation and oxidation resistance were induced by ACh under salt stress. The genes whose transcript levels were elevated by ACh treatment in salt-stressed N. benthamiana could be used as molecular markers of the physiological status of plants under salt stress.

Integration of silicon and secondary metabolites in plants: a significant association in stress tolerance.

As sessile organisms, plants are unable to avoid being subjected to environmental stresses that negatively affect their growth and productivity. Instead, they utilize various mechanisms at the morphological, physiological, and biochemical levels to alleviate the deleterious effects of such stresses. Amongst these, secondary metabolites produced by plants represent an important component of the defense system. Secondary metabolites, namely phenolics, terpenes, and nitrogen-containing compounds, have been extensively demonstrated to protect plants against multiple stresses, both biotic (herbivores and pathogenic microorganisms) and abiotic (e.g. drought, salinity, and heavy metals). The regulation of secondary metabolism by beneficial elements such as silicon (Si) is an important topic. Silicon-mediated alleviation of both biotic and abiotic stresses has been well documented in numerous plant species. Recently, many studies have demonstrated the involvement of Si in strengthening stress tolerance through the modulation of secondary metabolism. In this review, we discuss Si-mediated regulation of the synthesis, metabolism, and modification of secondary metabolites that lead to enhanced stress tolerance, with a focus on physiological, biochemical, and molecular aspects. Whilst mechanisms involved in Si-mediated regulation of pathogen resistance via secondary metabolism have been established in plants, they are largely unknown in the case of abiotic stresses, thus leaving an important gap in our current knowledge.

Mechanism of Allium Crops Bulb Enlargement in Response to Photoperiod: A Review.

The photoperiod marks a varied set of behaviors in plants, including bulbing. Bulbing is controlled by inner signals, which can be stimulated or subdued by the ecological environment. It had been broadly stated that phytohormones control the plant development, and they are considered to play a significant part in the bulb formation. The past decade has witnessed significant progress in understanding and advancement about the photoperiodic initiation of bulbing in plants. A noticeable query is to what degree the mechanisms discovered in bulb crops are also shared by other species and what other qualities are also dependent on photoperiod. The FLOWERING LOCUS T (FT) protein has a role in flowering; however, the FT genes were afterward reported to play further functions in other biological developments (e.g., bulbing). This is predominantly applicable in photoperiodic regulation, where the FT genes seem to have experienced significant development at the practical level and play a novel part in the switch of bulb formation in Alliums. The neofunctionalization of FT homologs in the photoperiodic environments detects these proteins as a new class of primary signaling mechanisms that control the growth and organogenesis in these agronomic-related species. In the present review, we report the underlying mechanisms regulating the photoperiodic-mediated bulb enlargement in Allium species. Therefore, the present review aims to systematically review the published literature on the bulbing mechanism of Allium crops in response to photoperiod. We also provide evidence showing that the bulbing transitions are controlled by phytohormones signaling and FT-like paralogues that respond to independent environmental cues (photoperiod), and we also show that an autorelay mechanism involving FT modulates the expression of the bulbing-control gene. Although a large number of studies have been conducted, several limitations and research gaps have been identified that need to be addressed in future studies.

Combined Kinetin and Spermidine Treatments Ameliorate Growth and Photosynthetic Inhibition in Vigna angularis by Up-Regulating Antioxidant and Nitrogen Metabolism under Cadmium Stress.

Pot experiments were conducted to investigate the probable beneficial role of the individual as well as combined application of kinetin (50 µM Kn) and spermidine (200 µM Spd) on Vigna angularis under cadmium (Cd) stress. Cd treatment reduced growth by declining the content of chlorophylls and carotenoids, photosynthesis, and gas exchange parameters. Exogenously, Kn and Spd application enhanced the photosynthetic parameters and up-regulated the antioxidant system by improving the activities of antioxidant enzymes and the content of non-enzymatic components. In addition, the application of Kn and Spd resulted in significant improvement in the content of sugars, proline, and glycine betaine, ameliorating the decline in relative water content. Oxidative stress parameters including hydrogen peroxide, superoxide, lipid peroxidation, lipoxygenase activity, and electrolyte leakage increased due to Cd stress; however, the application of Kn and Spd imparted a significant decline in all these parameters. Further, reduced Cd uptake was also observed due to Kn and Spd application. Total phenols and flavonoids also increased due to Kn and Spd treatments under normal as well as Cd stress conditions, which may have further helped with the elimination of reactive oxygen species. Reduction in the activity of nitrate reductase and the content of nitrogen was ameliorated due to the exogenous application of Kn and Spd. Therefore, the exogenous application of Kn and Spd benefited Vigna angularis counteracting the damaging effects of Cd stress by up-regulating the tolerance mechanisms, including antioxidant and osmolyte metabolism.

Sodium nitroprusside (SNP) improves tolerance to arsenic (As) toxicity in Vicia faba through the modifications of biochemical attributes, antioxidants, ascorbate-glutathione cycle and glyoxalase cycle.

The present study was conducted to evaluate the effect of arsenic (As) toxicity and the mitigating role of nitric oxide (NO) donor sodium nitroprusside (SNP) on Vicia faba. Arsenics stress decreased the growth and biomass yield, and photosynthetic pigments, but it enhanced As accumulation. Supplementation of NO enhanced the afore-mentioned parameters except As accumulation which decreased in both shoot and root. Supplementation of NO enhanced the shoot tolerance index (Shoot TI%), root tolerance index (Root TI%) but it declined the As translocation factor (TF). Application of NO alleviated the As-induced decline in net assimilation rate, stomatal conductance, transpiration and leaf relative water content. The levels of proline and glycine betaine (GB) further increased due to NO application, whereas malondialdehyde (MDA), hydrogen peroxide (H2O2), electrolyte leakage (EL) and methylglyoxal (MG) declined considerably. Activities of enzymatic antioxidants such as superoxide dismutase (SOD) and catalase (CAT) increased under As stress. Supplementation of NO up-regulated the enzymes involved in Asc-Glu cycle and glyoxalase cycle under As toxicity. Another experiment was setup to authenticate whether NO was certainly able to alleviate As toxicity. For this purpose, the NO scavenger [2-(4-carboxy-2 phenyl)-4,4,5,5-tertamethylimidazoline-1-oxyl-3-oxide (cPTIO)] was added to As and NO supplemented plants. Addition of cPTIO to NO supplemented As-treated plants showed the same effect when As alone was supplied to plants. In conclusion, addition of NO to the growth medium maintained the plant performance under As toxicity through modulation of physio-biochemical attributes, antioxidant enzymes, and the Asc-Glu and glyoxalase systems.

Combined effects of brassinosteroid and kinetin mitigates salinity stress in tomato through the modulation of antioxidant and osmolyte metabolism.

Salinity stress reduces growth and yield productivity of most crop plants. Potentiality of kinetin (Kn) and epi-brassinolide (EBL), either individually or combinedly in preventing the salinity (100 mM NaCl) stress mediated oxidative damage and photosynthetic inhibition was studied in Solanum lycopersicum. Combined application of Kn and EBL imparted much prominent impact on the growth, photosynthesis and metabolism of antioxidants, osmolytes and secondary metabolites. Synthesis of chlorophylls and carotenoids increased and the photosynthetic parameters like stomatal conductance, intercellular CO2 concentration and net photosynthesis were significantly improved due to application of Kn and EBL. Photosystem II functioning (Fv/Fm), photochemical quenching and electron transport rate (ETR) improved significantly in Kn and EBL treated plants imparting significant decline in salinity induced non-photochemical quenching. Exogenous Kn and EBL effectively prevented the oxidative damage by significantly declining the generation of hydrogen peroxide and superoxide under saline and non-saline conditions as reflected in lowered lipid peroxidation and electrolyte leakage. Reduced oxidative damage in Kn and EBL treated plants was accompanied down-regulation of protease and lipoxygenase concomitant with up-regulation of the antioxidant system and the accumulation of compatible osmolytes. Treatment of Kn and EBL proved effective in enhancing the contents of redox homeostasis, ascorbic acid and reduced glutathione, and the secondary metabolites assisting the enzymatic antioxidant system in combating the salinity stress efficiently. Results suggest that combined application of Kn and EBL regulate growth and photosynthesis in tomato more effectively than their individual application through a probable regulatory crosstalk mechanism.

Nitrogen availability prevents oxidative effects of salinity on wheat growth and photosynthesis by up-regulating the antioxidants and osmolytes metabolism, and secondary metabolite accumulation.

BACKGROUND: Salinity is one of the damaging abiotic stress factor. Proper management techniques have been proposed to considerably lower the intensity of salinity on crop growth and productivity. Therefore experiments were conducted to assess the role of improved nitrogen (N) supplementation on the growth and salinity stress tolerance in wheat by analyzing the antioxidants, osmolytes and secondary metabolites. RESULTS: Salinity (100 mM NaCl) stress imparted deleterious effects on the chlorophyll and carotenoid synthesis as well as the photosynthetic efficiency. N supplementation resulted in increased photosynthetic rate, stomatal conductance and internal CO2 concentration with effects being much obvious in seedlings treated with higher N dose. Under non-saline conditions at both N levels, protease and lipoxygenase activity reduced significantly reflecting in reduced oxidative damage. Such effects were accompanied by reduced generation of toxic radicals like hydrogen peroxide and superoxide, and lipid peroxidation in N supplemented seedlings. Antioxidant defence system was up-regulated under saline and non-saline growth conditions due to N supplementation leading to protection of major cellular processes like photosynthesis, membrane structure and function, and mineral assimilation. Increased osmolyte and secondary metabolite accumulation, and redox components in N supplemented plants regulated the ROS metabolism and NaCl tolerance by further strengthening the antioxidant mechanisms. CONCLUSIONS: Findings of present study suggest that N availability regulated the salinity tolerance by reducing Na uptake and strengthening the key tolerance mechanisms.

24-Epibrassinolide (EBR) Confers Tolerance against NaCl Stress in Soybean Plants by Up-Regulating Antioxidant System, Ascorbate-Glutathione Cycle, and Glyoxalase System.

: The present research was performed to assess the effect of 24-epibrassinolide (EBR) on salt-stressed soybean plants. Salt stress suppressed growth, biomass yield, gas exchange parameters, pigment content, and chlorophyll fluorescence, but all these parameters were up-regulated by EBR supply. Moreover, salt stress increased hydrogen peroxide, malondialdehyde, and electrolyte leakage. EBR supplementation reduced the accumulation of oxidative stress biomarkers. The activities of superoxide dismutase and catalase, and the accumulation of proline, glycinebetaine, total phenols, and total flavonoids increased with NaCl stress, but these attributes further increased with EBR supplementation. The activities of enzymes and the levels of non-enzymatic antioxidants involved in the Asc-Glu cycle also increased with NaCl stress, and further enhancement in these attributes was recorded by EBR supplementation. Salinity elevated the methylglyoxal content, but it was decreased by the EBR supplementation accompanying with up-regulation of the glyoxalase cycle (GlyI and GlyII). Salinity enhanced the Na+ uptake in root and shoot coupled with a decrease in uptake of Ca2+, K+, and P. However, EBR supplementation declined Na+ accumulation and promoted the uptake of the aforementioned nutrients. Overall, EBR supplementation regulated the salt tolerance mechanism in soybean plants by modulating osmolytes, activities of key enzymes, and the levels of non-enzymatic antioxidants.