Alleviation of salt-induced photosynthesis and growth inhibition by salicylic acid involves glycinebetaine and ethylene in mungbean (Vigna radiata L.)

Mitigation of Salinity Stress on Pomegranate (Punica granatum L. cv. Wonderful) Plant Using Salicylic Acid Foliar Spray

Salt stress significantly impacts plant morphological structure and physiological processes, resulting in decreased plant growth. Salicylic acid (SA) is a key signal molecule that protects plants from the negative impacts of salinity. Under natural conditions, the pomegranate plant generally exhibits salt-tolerant characteristics. The objective of this study was to elucidate the salt-tolerance level of pomegranate (Punica granatum L. cv. Wonderful) and the effect of the regulating strategy of SA foliar spray on growth, morphological structure, and physiological processes. SA levels were 0, 0.25, 0.50, and 1 mM in the presence of salinity levels of 10, 35, and 70 mM NaCl, respectively. Vegetative growth indices, including stem cross-sectional area, leaf area, and total dry weight, were lowered by salinity treatments. However, SA applications greatly improved morphological characteristics and plant growth under salt stress. The effects of salinity were effectively reversed by SA treatment at 1 mM compared to control and other treatments. Interestingly, SA applications enhanced the chlorophyll, total phenolic, carbohydrate, and proline contents of leaves while decreasing electrolyte leakage (EL), Na, and Cl levels. Moreover, the foliar SA treatments enhanced the nutrient content in the leaves and increased the activities of peroxidase (POD) and catalase (CAT), with a decrease in malondialdehyde (MDA) content. This study suggests that the alleviation of the salinity stress by SA may be due to the activation of the antioxidant enzymatic mechanism and decrease in the lipid peroxidation of the pomegranate plant.

Seed Germination Behavior, Growth, Physiology and Antioxidant Metabolism of Four Contrasting Cultivars under Combined Drought and Salinity in Soybean

Drought and salinity stresses are persistent threat to field crops and are frequently mentioned as major constraints on worldwide agricultural productivity. Moreover, their severity and frequency are predicted to rise in the near future. Therefore, in the present study we investigated the mechanisms underlying plant responses to drought (5, 10 and 15% polyethylene glycol, PEG-6000), salinity (50, 100, and 150 mM NaCl), and their combination, particularly at the seed germination stage, in terms of photosynthesis and antioxidant activity, in four soybean cultivars, viz., PI408105A (PI5A), PI567731 (PI31), PI567690 (PI90), and PI416937 (PI37). Results showed that seed germination was enhanced by 10% PEG and decreased by 15% PEG treatments compared to the control, while seed germination was drastically decreased under all levels of NaCl treatment. Furthermore, combined drought and salinity treatment reduced plant height and root length, shoot and root total weights, and relative water content compared with that of control. However, the reductions were not similar among the varieties, and definite growth retardations were observed in cultivar PI5A under drought and in PI37 under salinity. In addition, all treatments resulted in substantially reduced contents of chlorophyll pigment, anthocyanin, and chlorophyll fluorescence; and increased lipid peroxidation, electrolyte leakage, and non-photochemical quenching in all varieties of soybean as compared to the control plants. However, proline, amino acids, sugars, and secondary metabolites were increased with the drought and salinity stresses alone. Moreover, the reactive oxygen species accumulation was accompanied by improved enzymatic antioxidant activity, such as that of superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase. However, the enhancement was most noticeable in PI31 and PI90 under both treatments. In conclusion, the cultivar PI31 has efficient drought and salinity stress tolerance mechanisms, as illustrated by its superior photosynthesis, osmolyte accumulation, antioxidative enzyme activity, and secondary metabolite regulation, compared to the other cultivars, when stressed.

Utilization of drought-tolerant bacterial strains isolated from harsh soils as a plant growth-promoting rhizobacteria (PGPR)

Drought stress adversely affects plant health and productivity. Recently, drought-resistant bacterial isolates are used to combat drought resistance in crops. In this in vitro study, 20 bacterial isolates were isolated from harsh soil; their drought tolerance was evaluated using four concentrations of polyethylene glycol (PEG) 6000. The two most efficient isolates (DS4 and DS9) were selected and identified using 16S rRNA genetic sequencing. They were registered in the NCBI database and deposited under accession numbers MW916285 and MW916307 for Bacillus cereus (DS4) and Bacillus albus (DS9), respectively. These isolates were screened for plant growth-promoting properties compared to non-stressed conditions. Biochemical parameters; Proline, salicylic acid, gibberellic acid (GA), indole acetic acid (IAA), antioxidant activity, and antioxidant enzymes were measured under the same conditions, and in vitro seed germination was tested under stress conditions and inoculation with selected isolates. The results showed that under the harsh conditions of PEG6000, DS4 produced the highest amount of IAA of 1.61 µg/ml, followed by DS9 with 0.9 µg/ml. The highest amount of GA (49.95 µg/ml) was produced by DS9. On the other hand, the highest amount of siderophore was produced from DS4 isolate followed by DS9. Additionally, DS4 isolate recorded the highest exopolysaccharide (EPS) content of 3.4 mg/ml under PEG (-1.2 MPa) followed by DS9. The antioxidant activity increased in PEG concentrations depending manner, and the activity of the antioxidant enzymes increased, as catalase (CAT) recorded the highest activity in DS4 with an amount of 1.095 mg/ml. additionally, an increase in biofilm formation was observed under drought conditions. The isolated mixture protected the plant from the harmful effects of drought and showed an increase in the measured variables. Under unstressed conditions, the highest rates of emulsification index (EI 24%) were obtained for DS4 and DS9, at 14.92 and 11.54, respectively, and decreased under stress. The highest values of germination, total seedling length, and vigor index were obtained upon inoculation with the combination of two strains, and were 100%, 4.10 cm, and 410, respectively. Therefore, two strains combination is an effective vaccine capable of developing and improving drought tolerance in dryland plants.

Ethylene involvement in the regulation of heat stress tolerance in plants

Because of the rise in global temperature, heat stress has become a major concern for crop production. Heat stress deteriorates plant productivity and alters phenological and physiological responses that aid in precise monitoring and sensing of mild-to-severe transient heat stress. Plants have evolved several sophisticated mechanisms including hormone-signaling pathways to sense heat stimuli and acquire heat stress tolerance. In response to heat stress, ethylene, a gaseous hormone, is produced which is indispensable for plant growth and development and tolerance to various abiotic stresses including heat stress. The manipulation of ethylene in developing heat stress tolerance targeting ethylene biosynthesis and signaling pathways has brought promising out comes. Conversely increased ethylene biosynthesis and signaling seem to exhibit inhibitory effects in plant growth responses from primitive to maturity stages. This review mainly focuses on the recent studies of ethylene involvement in plant responses to heat stress and its functional regulation, and molecular mechanism underlying the plant responses in the mitigation of heat-induced damages. Furthermore, this review also describes the crosstalk between ethylene and other signaling molecules under heat stress and approaches to improve heat stress tolerance in plants.

Foliar Application of Salicylic Acid Improves Salt Tolerance of Sorghum (Sorghum bicolor (L.) Moench)

It has been reported that around the world, approximately 19.5% of all irrigated land and 2.1% of dry land is affected by salt stress, and these percentages continue to increase. Sorghum is the fifth most important cereal in the world and therefore research on its salt tolerance is of global importance. In our research, we focused on foliar application of salicylic acid (SA) on salt-stressed sorghum. We performed a pot experiment with two salt levels (0 and 100 mM sodium chloride NaCl) and five SA concentrations (0, 50, 100, 150 and 200 mg/L). Our results suggest that in saline conditions foliar application of SA induced an adaptive response to salinity by inducing proline accumulation as well as antioxidant enzymes activities and enhanced the protection of the photosynthetic machinery, maintained photosynthesis activities, and improved the growth of sorghum plants. These alleviation effects were depended on applied SA concentration. Under saline condition 150 mg/L, SA was the most effective for relieving the adverse effect of salt stress. Under non-saline conditions 100 mg/L SA was the best for improving sorghum growth and dry matter production. Our results demonstrated that foliar SA application is effective in improving sorghum growth under salinity.

Impact of Exogenously Sprayed Antioxidants on Physio-Biochemical, Agronomic, and Quality Parameters of Potato in Salt-Affected Soil

Salinity is one of the harsh environmental stresses that destructively impact potato growth and production, particularly in arid regions. Exogenously applied safe-efficient materials is a vital approach for ameliorating plant growth, productivity, and quality under salinity stress. This study aimed at investigating the impact of foliar spray using folic acid (FA), ascorbic acid (AA), and salicylic acid (SA) at different concentrations (100, 150, or 200 mg/L) on plant growth, physiochemical ingredients, antioxidant defense system, tuber yield, and quality of potato (Solanum tuberosum L cv. Spunta) grown in salt-affected soil (EC = 7.14 dS/m) during two growing seasons. The exogenously applied antioxidant materials (FA, AA, and SA) significantly enhanced growth attributes (plant height, shoot fresh and dry weight, and leaves area), photosynthetic pigments (chlorophyll a and b and carotenoids), gas exchange (net photosynthetic rate, Pn; transpiration rate, Tr; and stomatal conductance, gs), nutrient content (N, P, and K), K+/ Na+ ratio, nonenzymatic antioxidant compounds (proline and soluble sugar content), enzymatic antioxidants (catalase (CAT), peroxidase (POX), superoxide dismutase (SOD), and ascorbate peroxidase (APX)) tuber yield traits, and tuber quality (dry matter, protein, starch percentage, total carbohydrates, and sugars percentage) compared with untreated plants in both seasons. Otherwise, exogenous application significantly decreased Na+ and Cl- compared to the untreated control under salt stress conditions. Among the assessed treatments, the applied foliar of AA at a rate of 200 mg/L was more effective in promoting salt tolerance, which can be employed in reducing the losses caused by salinity stress in potato grown in salt-affected soils.

To Fight or to Grow: The Balancing Role of Ethylene in Plant Abiotic Stress Responses

Plants often live in adverse environmental conditions and are exposed to various stresses, such as heat, cold, heavy metals, salt, radiation, poor lighting, nutrient deficiency, drought, or flooding. To adapt to unfavorable environments, plants have evolved specialized molecular mechanisms that serve to balance the trade-off between abiotic stress responses and growth. These mechanisms enable plants to continue to develop and reproduce even under adverse conditions. Ethylene, as a key growth regulator, is leveraged by plants to mitigate the negative effects of some of these stresses on plant development and growth. By cooperating with other hormones, such as jasmonic acid (JA), abscisic acid (ABA), brassinosteroids (BR), auxin, gibberellic acid (GA), salicylic acid (SA), and cytokinin (CK), ethylene triggers defense and survival mechanisms thereby coordinating plant growth and development in response to abiotic stresses. This review describes the crosstalk between ethylene and other plant hormones in tipping the balance between plant growth and abiotic stress responses.

Haematococcus pluvialis Accumulated Lipid and Astaxanthin in a Moderate and Sustainable Way by the Self-Protection Mechanism of Salicylic Acid Under Sodium Acetate Stress

To elucidate the mechanism underlying increased fatty acid and astaxanthin accumulation in Haematococcus pluvialis, transcriptome analysis was performed to gain insights into the multiple defensive systems elicited by salicylic acid combined with sodium acetate (SAHS) stresses with a time course. Totally, 112,886 unigenes and 61,323 non-repeat genes were identified, and genes involved in carbon metabolism, primary and secondary metabolism, and immune system responses were identified. The results revealed that SA and NaAC provide both energy and precursors to improve cell growth of H. pluvialis and enhance carbon assimilation, astaxanthin, and fatty acids production in this microalga with an effective mechanism. Interestingly, SA was considered to play an important role in lowering transcriptional activity of the fatty acid and astaxanthin biosynthesis genes through self-protection metabolism in H. pluvialis, leading to its adaption to HS stress and finally avoiding massive cell death. Moreover, positive correlations between 15 key genes involved in astaxanthin and fatty acid biosynthesis pathways were found, revealing cooperative relation between these pathways at the transcription level. These results not only enriched our knowledge of the astaxanthin accumulation mechanism in H. pluvialis but also provided a new view on increasing astaxanthin production in H. pluvialis by a moderate and sustainable way in the future.

Trichoderma longibrachiatum (TG1) Enhances Wheat Seedlings Tolerance to Salt Stress and Resistance to Fusarium pseudograminearum

Salinity is abiotic stress that inhibits seed germination and suppresses plant growth and root development in a dose-dependent manner. Fusarium pseudograminearum (Fg) is a plant pathogen that causes wheat crown rot. Chemical control methods against Fg are toxic to the environment and resistance has been observed in wheat crops. Therefore, an alternative approach is needed to manage this devastating disease and the effects of salinity. Our research focused on the mycoparasitic mechanisms of Trichoderma longibrachiatum (TG1) on Fg and the induction of defenses in wheat seedlings under salt and Fg stress at physiological, biochemical and molecular levels. The average inhibition rate of TG1 against Fg was 33.86%, 36.32%, 44.59%, and 46.62%, respectively, in the four NaCl treatments (0, 50, 100, and 150 mM). The mycoparasitic mechanisms of TG1 against Fg were coiling, penetration, and wrapping of Fg hyphae. In response to inoculation of TG1 with Fg, significant upregulation of cell wall degrading enzymes (CWDEs) was observed. The expression of β-1, 6-glucan synthase (PP4), endochitinase precursor (PH-1), and chitinase (chi18-15) increased by 1. 6, 1. 9, and 1.3-fold on day 14 compared with day 3. Wheat seedlings with combined TG1 + Fg treatments under different NaCl stress levels decreased disease index by an average of 51.89%; increased the superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activity by an average of 38%, 61%, and 24.96%, respectively; and decreased malondialdehyde (MDA) and hydrogen peroxide (H2O2) content by an average of 44.07% and 41.75% respectively, compared with Fg treated seedlings. The combined TG1 + Fg treatment induced the transcription level of plant defense-related genes resulting in an increase in tyrosin-protein kinase (PR2), chitinase class I (CHIA1), and pathogenesis-related protein (PR1-2) by an average of 1.15, 1.35, and 1.37-fold, respectively compared to Fg treatment. However, the expression levels of phenylalanine ammonia-lyase (PAL) increased 3.40-fold under various NaCl stresses. Our results suggest that TG1 enhances wheat seedling growth and controls wheat crown rot disease by strengthening the plant defense system and upregulating the expression of pathogenesis-related genes under both Fg and salt stress.

Land Suitability Assessment for Pulse (Green Gram) Production through Remote Sensing, GIS and Multicriteria Analysis in the Coastal Region of Bangladesh

The agricultural potential of Bangladesh’s coastal region has been threatened by the impact of climate change. Pulse crops with high nutritional value and low production costs such as green gram constitute an important component of a healthy and accessible diet for the country. In order to optimize the production of this important staple, this research aims to promote climate-smart agriculture by optimizing the identification of the appropriate land. The objective of this research is to investigate, estimate, and identify the suitable land areas for green gram production based on the topography, climate, and soil characteristics in the coastal region of Bangladesh. The methodology of the study included a Geographic Information System (GIS) and the Multicriteria Decision-Making approach: the Analytical Hierarchy Process (AHP). Datasets were collected and prepared using Landsat 8 imagery, the Center for Hydrometeorology and Remote Sensing (CHRS) data portal and the Bangladesh Agricultural Research Council. All the datasets were processed into raster images and then reclassified into four classes: Highly Suitable (S1), Moderately Suitable (S2), Marginally Suitable (S3), and Not Suitable. Then, the AHP results were applied to produce a final green gram suitability map with four classes of suitability. The results of the study found that 12% of the coastal area (344,619.5 ha) is highly suitable for green gram production, while the majority of the land area (82.3% of the area) shows moderately suitable (S2) land. The sensitivity analysis results show that 3.3%, 63.4%, 28.0%, and 1.2% of the study area are S1, S2, S3, and NS, respectively. It is also found that the highly suitable land area belongs mostly to the southeastern part of the country. The result of this study can be utilized by policymakers to adopt a proper green gram production strategy, providing special agricultural incentive policies in the highly suitable area as a provision for the increased food production of the country.

Nanobiotechnological Approaches to Enhance Potato Resistance against Potato Leafroll Virus (PLRV) Using Glycyrrhizic Acid Ammonium Salt and Salicylic Acid Nanoparticles

The present research was aiming to study In-Silico the effect of Glycyrrhizic Acid ammonium salt (GAS) and Salicylic acid (SA) on the coat protein of potato leafroll virus (PLRV). In addition, in-vitro studying the effect of (GAS NPs) and Salicylic acid (SA NPs) nanoparticles at concentrations 0.15, 0.30, 1.25 and 2.5 mM, respectively, to control, decline or reduce the presence of PLRV in potato plants Solanum tuberosum L. selena. (GAS NPs) and (SA NPs) were applied in the MS medium at concentrations 0.15, 0.30, 1.25 and 2.5 mM, respectively. Results revealed that, enhancement or decline the PLRV according to the initiation of specific pathways. The expression level of Kinase 3 gene increased significantly due to the two used concentrations of GAS NPs. While the expression of callose gene was upregulated significantly in response to treatment of PLRV infected plant with (GAS NPs) with concentration (0.30 mM). Treatment with (SA NPs) caused upregulation significance only of callose gene at (2.5 mM) concentration. The molecular modeling results of used compounds (glycyrrhizic acid ammonium salt and salicylic acid) showed highest score of binding and the best rms define value with a very good binding mode and perfect interactions with amino acids of the three subunits (A, B and C) forming the protein coat of leaf roll virus. Glycyrrhizic acid ammonium salt and salicylic acid nanoparticles could be perfect solution to produce potato plant free virus in-vitro. Further larger studies are needed to investigate the role of the studied compounds in vivo.

Control of Elevated Ion Accumulation, Oxidative Stress, and Lipid Peroxidation with Salicylic Acid-Induced Accumulation of Glycine Betaine in Salinity-Exposed Vigna radiata L

The identification of the sustainable approaches is required for the minimization of adverse impact of worldwide increasing soil salinity on plant growth, development, and productivity. This study investigated the protective role and major mechanism underlying salicylic acid (SA; 0.1, 0.5, or 1.0 mM)-induced glycine betaine (GB)-mediated tolerance to salinity (50 mM NaCl) in mungbean (Vigna radiata L. cultivar Punt Mung). The supply of 0.5 mM SA maximally increased the accumulation of GB (>40%) with respect to the control. This was further corroborated with the increase in water potential, antioxidant system (reduced glutathione (GSH), GSH/GSSG redox state, and glutathione reductase (GR) activity) and decreased Na+ and Cl- accumulation, Na+/K+ ratio, oxidative stress, and lipid peroxidation. This was also associated with the increased photosynthesis (14-18%) and growth (7-12%) parameters. Overall, SA-induced accumulation of GB protected photosynthesis and growth against 50 mM NaCl-accrued impacts in V. radiata through minimizing the accumulation of Na+ and Cl- ions, oxidative stress, and maintaining high GSH level that led to reduced cellular redox environment.

Potassium: A track to develop salinity tolerant plants

Salinity is one of the major constraints to plant growth and development across the globe that leads to the huge crop productivity loss. Salinity stress causes impairment in plant's metabolic and cellular processes including disruption in ionic homeostasis due to excess of sodium (Na⁺) ion influx and potassium (K⁺) efflux. This condition subsequently results in a significant reduction of the cytosolic K⁺ levels, eventually inhibiting plant growth attributes. K⁺ plays a crucial role in alleviating salinity stress by recasting key processes of plants. In addition, K⁺ acquisition and retention also serve as the perquisite trait to establish salt tolerant mechanism. In addition, an intricate network of genes and their regulatory elements are involved in coordinating salinity stress responses. Furthermore, plant growth regulators (PGRs) and other signalling molecules influence K⁺-mediated salinity tolerance in plants. Recently, nanoparticles (NPs) have also been found several implications in plants with respect to their roles in mediating K⁺ homoeostasis during salinity stress in plants. The present review describes salinity-induced adversities in plants and role of K⁺ in mitigating salinity-induced damages. The review also highlights the efficacy of PGRs and other signalling molecules in regulating K⁺ mediated salinity tolerance along with nano-technological perspective for improving K⁺ mediated salinity tolerance in plants.

Crosstalk of plant growth regulators protects photosynthetic performance from arsenic damage by modulating defense systems in rice

Salicylic acid (SA) is a well-known plant growth regulator, which participates in many physiological processes of plants under normal and stressful conditions. In this study, we investigated the impact of SA supplementation on the components of ascorbate-glutathione cycle and glyoxalase system, photosynthesis and growth of rice (Oryza sativa) plants subjected to arsenic (As) stress. Plants grown with As exhibited enhanced As uptake, increased oxidative stress, and photosynthesis and growth inhibition. Application of SA promoted photosynthesis and growth in plants with or without As stress by improving plant defense systems and reducing oxidative stress through interaction with ethylene and nitric oxide (NO). SA acted as an ethylene antagonist, reducing stress ethylene formation under As stress, while NO formation was induced. This resulted in coordinated control over the antioxidant defense systems and enhanced As tolerance, protecting photosynthesis and growth from As-induced damage. The study showed that positive responses of SA in promoting photosynthesis and growth under As stress were the result of its interplay with ethylene and NO, enhanced capacity of defense systems to reduce oxidative stress. The crosstalk of SA with ethylene and NO will be useful in augmenting the performance of rice plants under As stress.

Priming with Nanoscale Materials for Boosting Abiotic Stress Tolerance in Crop Plants

Seed priming is a cost-effective, practical, environmental, and farmer-friendly method to improve seed germination that can potentially increase the growth and yield of plants. The priming process enhances various physiological and biochemical mechanisms of defense and empowers the seeds or seedlings to overcome different environmental stresses. However, under critical circumstances, plants are hindered from absorbing specific chemical priming reagents owing to their larger size, molecular structure, or lack of carriers. Therefore, nanoscale materials having exceptional physiochemical properties and a large surface/volume ratio are expected to be better absorbed by the seeds/seedlings as priming agents in comparison to bulk chemicals and can trigger enhanced molecular interactions at the cellular level. Further, the flexibility in altering the surface chemical properties of the nanomaterials can facilitate better interaction with the seeds/seedlings while inhibiting the wastage of priming agents. In this review, we have systematically discussed the potentiality of various nanostructured materials as priming agents in alleviating the adverse effects of various abiotic stresses, viz., drought, salinity, high temperature, cold temperature, and heavy metals, by studying the growth parameters and physiological and biochemical response of various crop plants subjected to these stress conditions. Also, we have highlighted the molecular mechanism and activation of genes involved in enabling abiotic stress tolerance in plants after being primed with nanostructured materials.

Coordinated Role of Nitric Oxide, Ethylene, Nitrogen, and Sulfur in Plant Salt Stress Tolerance

Salt stress significantly contributes to major losses in agricultural productivity worldwide. The sustainable approach for salinity-accrued toxicity has been explored. The use of plant growth regulators/phytohormones, mineral nutrients and other signaling molecules is one of the major approaches for reversing salt-induced toxicity in plants. Application of the signaling molecules such as nitric oxide (NO) and ethylene (ETH) and major mineral nutrient such as nitrogen (N) and sulfur (S) play significant roles in combatting the major consequences of salt stress impacts in plants. However, the literature available on gaseous signaling molecules (NO/ETH) or/and mineral nutrients (N/S) stands alone, and major insights into the role of NO or/and ETH along with N and S in plant-tolerance to salt remained unclear. Thus, this review aimed to (a) briefly overview salt stress and highlight salt-induced toxicity, (b) appraise the literature reporting potential mechanisms underlying the role of gaseous signaling molecules and mineral nutrient in salt stress tolerance, and (c) discuss NO and ETH along with N and S in relation to salt stress tolerance. In addition, significant issues that have still to be investigated in this context have been mentioned.

Abscisic Acid in Coordination with Nitrogen Alleviates Salinity-Inhibited Photosynthetic Potential in Mustard by Improving Proline Accumulation and Antioxidant Activity

This investigation was done to assess the role of abscisic acid (ABA; 25 µM) and/or nitrogen (N; 10 mM) in the alleviation of salinity (NaCl; 100 mM)-induced reduction in photosynthetic activity and growth, N and sulfur (S) assimilation of mustard (Brassica juncea L.) cv. RH0-749. Salinity treatment caused oxidative stress and significantly elevated the content of both H2O2 and thiobarbituric acid reactive substances (TBARS), and impaired photosynthetic activity and growth, but increased the content of nitrogenous osmolyte proline and the activity of antioxidant enzymes involved in the metabolism of reactive oxygen species. The application of 25 µM ABA under a controlled condition negatively affected photosynthesis and growth. However, ABA, when combined with N, minimized oxidative stress and mitigated the salinity-inhibited effects by increasing the activity of antioxidant enzymes (superoxide dismutase, SOD; glutathione reductase, GR; ascorbate peroxidase, APX) and proline content. Overall, the supplementation of 10 mM N combined with 25 µM ABA provides an important strategy for enhancing the photosynthetic potential of B. juncea under saline conditions.

Integrated transcriptomics and metabolomics analysis to characterize alkali stress responses in canola (Brassica napus L.)

BACKGROUND

Soil salinization is a major constraint limiting agricultural development and affecting crop growth and productivity, especially in arid and semi-arid regions. Understanding the molecular mechanism of the adaptability of canola to salt stress is very important to improve the salt tolerance of canola and promote its cultivation in saline alkali soil.

RESULTS

To identify the metabolomic and transcriptomic mechanisms of canola under alkaline salt stress, we collected roots of control (no salt treatment) and 72 h Na₂CO₃-stressed canola seedlings (hydroponics) for metabolic profiling of metabolites, supplemented with RNA-Seq analysis and real-time quantitative PCR validation. Metabolomic analysis showed that the metabolites of amino acids and fatty acids were higher accumulated under alkaline salt stress, including L-proline, L-glutamate, L-histidine, L-phenylalanine, L-citrulline, L-tyrosine, L-saccharopine, L-tryptophan, linoleic acid, dihomo gamma linolenic acid, alpha linolenic acid, Eric acid, oleic acid and neuronic acid, while the metabolism of carbohydrate (sucrase, alpha, alpha trehalose), polyol (ribitol), UDP-D-galactose, D-mannose, D-fructose and D-glucose 6-phosphate decreased. Transcriptomic and metabolomic pathway analysis indicated that carbohydrate metabolism may not play an important role in the resistance of canola to alkaline salt stress. Organic acid metabolism (fatty acid accumulation) and amino acid metabolism are important metabolic pathways in the root of canola under alkaline salt stress.

CONCLUSIONS

These results suggest that the genes and metabolites involved in fatty acid metabolism and amino acids metabolism in roots of canola may regulate salt tolerance of canola seedlings under alkaline salt stress, which improves our understanding of the molecular mechanisms of salt tolerance in canola.

Modulation of salt-induced stress impact in Gladiolus grandiflorus L. by exogenous application of salicylic acid

Salinity is challenging threats to the agricultural system and leading cause of crop loss. Salicylic acid (SA) is an important endogenous signal molecule, which by regulating growth and physiological processes improves the plant ability to tolerate salt stress. Considering the prime importance of Gladiolus grandiflorus (L.) in the world's cut-flower market, the research work was undertaken to elucidate salinity tolerance in G. grandiflorus by exogenous application of SA irrigated with saline water. Results revealed that increasing salinity (EC: 2, 4 and 6 dS m^-1) considerably altered morpho-growth indices (corm morphology and plant biomass) in plants through increasing key antioxidants including proline content and enzymes activity (superoxide dismutase, catalase and peroxidase), while negatively affected the total phenolic along with activity of defense-related enzymes (phenylalanine ammonia lyase, and polyphenol oxidase activity). SA application (50-200 ppm) in non-saline control or saline conditions improved morpho-physiological traits in concentration-dependent manners. In saline conditions, SA minimized salt-stress by enhancing chlorophyll content, accumulating organic osmolytes (glycine betaine and proline content), total phenolic, and boosting activity of antioxidant and defense-related enzymes. Principle component analysis based on all 16 morphological and physiological variables generated useful information regarding the classification of salt tolerant treatment according to their response to SA. These results suggest SA (100 or 150 ppm) could be used as an effective, economic, easily available and safe phenolic agent against salinity stress in G. grandiflorus.

Ethylene Supplementation Combined with Split Application of Nitrogen and Sulfur Protects Salt-Inhibited Photosynthesis through Optimization of Proline Metabolism and Antioxidant System in Mustard (Brassica juncea L.)

In the present study, the potential of ethylene as ethephon (an ethylene source) was investigated individually and in combination with split doses of nitrogen (N) and sulfur (S) soil treatments for removal of the damaging effects of salt stress (100 mM NaCl) in mustard (Brassica juncea L.). Plants were grown with 50 mg N plus 50 mg S kg^-1 soil at sowing time and an equivalent dose at 20 days after sowing [N50 + S50]_{0d and 20d}. Ethephon at 200 μL L^‒1 was applied to combined split doses of N and S with or without NaCl. Plants subjected to NaCl showed a decrease in growth and photosynthetic characteristics as well as N and S assimilation, whereas proline metabolism and antioxidants increased. The application of ethephon to plants grown with split N and S doses significantly enhanced photosynthetic efficiency by increasing the assimilation of N and S, improving the concentration of proline and induction of the antioxidant system with or without NaCl. The regulation of ethylene and/or split forms of N and S application may be potential tools for not just overcoming salt stress effects in this species and in related Brassicaceae but also enhancing their photosynthesis and growth potential through increased nutrient assimilation.

Study of the capacity of the essential oil of Lantana montevidensis to modulate the action of fluconazole on Candida albicans and Candida tropicalis strains

In recent decades, fungal infections have been increasing, as well as the indiscriminate use of large-scale antifungal. The objective of the present study was to characterize the chemical components of L. montevidensis leaf essential oil (EOLm) and evaluate its antifungal potential and fluconazole modulating activity against Candida strains. The essential oil was obtained by hydrodistillation and its chemical components were determined by Gas Chromatography coupled to Mass Spectrometry. The antifungal activity was determined by the microdilution method to determine the minimum inhibitory concentration. The modulatory activity of fluconazole by the oil (EOLm) was evaluated against the four Candida strains. Our results demonstrated a predominance of β-Caryophyllene (34.96%) and Germacrene D (25.49%), while (E)-Caryophyllene (0.08%) and δ-Cadinene (0.13%) were the minor constituents. For the antifungal activity, it was evidenced that the EOLm did not inhibit the growth of Candida albicans (CA LM 77 and CA INQS 40006) and Candida tropicalis (CT INCQS 40042 and CT LM 23), but, potentiated the effect of fluconazole in particular against C. tropicalis, although the FIC index indicates indifferent modulation for all strains tested. This study strongly suggests that administration of the fluconazole in combination with plant essential oils can provide a new opportunity to improve the outcome of the drug effect.

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.

β-Sitosterol differentially regulates key metabolites for growth improvement and stress tolerance in rice plants during prolonged UV-B stress

BACKGROUND

Elevated ultraviolet-B (UV-B) radiation is potentially deleterious to many organisms specifically crop plants and has become a global challenge. Rice is an exceptionally important staple food which is grown worldwide, and many efforts have been done recently to improve rice varieties against UV-B stress. This current study aims to investigate the effects of exogenous application of β-sitosterol (βSito) on growth improvement and tolerance level of rice plants against prolonged UV-B stress. The physiological and metabolic responses were evaluated in rice plants not supplemented with βSito (Nβ) and those supplemented with βSito (Sβ).

RESULTS

The Nβ and Sβ plants were grown under non-stress (ns) and under prolonged UV-B stress (uvs) conditions and termed as Nβ^ns, Sβ^ns and Nβ^uvs, Sβ^uvs, respectively. The application of βSito contributes positively under non-stress and specifically to UV-B stress in terms of improving numerous physiological parameters associated with growth and development such as shoot and root length, RWC, whole plant biomass, chlorophyll pigments, and photosynthetic-related parameters (Pn, Gs, Tr, WUEi, Fv/Fm, and NPQ) in Sβ compared with Nβ plants. Moreover, enhanced oxidative stress tolerance of Sβ^uvs vs. Nβ^uvs plants under stress was attributed to low levels of ROS and substantial trigger in activities of antioxidant enzymes (SOD, POD, CAT, and APX). Metabolic analysis was performed using GC-TOFMS, which revealed higher accumulation of several key metabolites including organic acids, sugars, amino acids, and others in Sβ^uvs vs. Nβ^uvs plants, which were mainly reduced in Nβ plants under stress vs. non-stress conditions.

CONCLUSION

These results provide useful data regarding the important role of βSito on growth maintenance and modulation of several metabolites associated with osmotic and redox adjustments during UV-B stress tolerance in rice plants. Importantly, βSito-regulated plasticity could further be explored specifically in relation to different environmental stresses in other economically useful crop plants.

SA-Mediated Regulation and Control of Abiotic Stress Tolerance in Rice

Environmental or abiotic stresses are a common threat that remains a constant and common challenge to all plants. These threats whether singular or in combination can have devastating effects on plants. As a semiaquatic plant, rice succumbs to the same threats. Here we systematically look into the involvement of salicylic acid (SA) in the regulation of abiotic stress in rice. Studies have shown that the level of endogenous salicylic acid (SA) is high in rice compared to any other plant species. The reason behind this elevated level and the contribution of this molecule towards abiotic stress management and other underlying mechanisms remains poorly understood in rice. In this review we will address various abiotic stresses that affect the biochemistry and physiology of rice and the role played by SA in its regulation. Further, this review will elucidate the potential mechanisms that control SA-mediated stress tolerance in rice, leading to future prospects and direction for investigation.

Comparison and Characterization of a Cell Wall Invertase Promoter from Cu-Tolerant and Non-Tolerant Populations of Elsholtzia haichowensis

Cell wall invertase (CWIN) activity and the expression of the corresponding gene were previously observed to be significantly elevated in a Cu-tolerant population of Elsholtzia haichowensis relative to a non-tolerant population under copper stress. To understand the differences in CWIN gene regulation between the two populations, their CWIN promoter β-glucuronidase (GUS) reporter vectors were constructed. GUS activity was measured in transgenic Arabidopsis in response to copper, sugar, and phytohormone treatments. Under the copper treatment, only the activity of the CWIN promoter from the Cu-tolerant population was slightly increased. Glucose and fructose significantly induced the activity of CWIN promoters from both populations. Among the phytohormone treatments, only salicylic acid induced significantly higher (p < 0.05) activity of the Cu-tolerant CWIN promoter relative to the non-tolerant promoters. Analysis of 5′-deletion constructs revealed that a 270-bp promoter fragment was required for SA induction of the promoter from the Cu-tolerant population. Comparison of this region in the two CWIN promoters revealed that it had 10 mutation sites and contained CAAT-box and W-box cis-elements in the Cu-tolerant promoter only. This work provides insights into the regulatory role of SA in CWIN gene expression and offers an explanation for differences in CWIN expression between E. haichowensis populations.

Mitigation of saline conditions in watermelon with mycorrhiza and silicon application

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Salt stress effects agronomic traits and uptake of minerals.

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Salt stress also enhanced the oxidative stress biomarkers like hydrogen peroxide (H₂O₂).

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Supplementation of Mycorrhiza enhances the agronomical traits and alleviates slat stress.

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Silicon application also mitigates the salt stress through modulating antioxidant enzymes.

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The combination of Mycorrhiza and Silicon were more effective than their individual effect.

Citrullus lanatus L. is critical vegetable for salinity stress. Arbuscular mycorrhizal fungi (AMF) and silicon treatments are known to help as bio-ameliorator of saline soils that can improve salinity tolerance in plants. But their combined effect has never been examined on watermelon therefore, present study investigated the effect of inoculation with the Arbuscular mycorrhizal fungi (AMF) along with silicon on the growth and yield parameters, antioxidant enzyme activities, pigment and mineral content of Citrullus lanatus L. plants grown during salt stress conditions. Outcomes from the study point out that salt stressed watermelon plants showed the best morphological and biochemical values when inoculated with Silicon (4 mM) + Glomus mosseae + Gigaspora gigantean. In addition, the plants inoculated by similar treatment demonstrated less osmotic activity, electrolyte leakage, as well as peroxide content. Treatments comprising Silicon (4 mM) with either Glomus mosseae and Gigaspora gigantean also performed significantly similar for most of the traits studied in the present investigation and better than the treatment only with either one of Glomus mosseae and Gigaspora gigantean. Antioxidant efficiency of melon was certainly appreciably enhanced after incubation with AMF and Si combination in salinity stress. Overall, the application of mycorrhiza and silicon can be considered to overcome the salinity stress in watermelon.

The intricacy of silicon, plant growth regulators and other signaling molecules for abiotic stress tolerance: An entrancing crosstalk between stress alleviators

Unfavorable environmental conditions are the critical inimical to the sustainable agriculture. Among various novel strategies designed to protect plants from abiotic stress threats, use of mineral elements as 'stress mitigators' has emerged as the most crucial and interesting aspect. Silicon (Si) is a quasi-essential nutrient that mediates plant growth and development and interacts with plant growth regulators (PGRs) and signaling molecules to combat abiotic stress induced adversities in plants and increase stress tolerance. PGRs are one of the most important chemical messengers that mediate plant growth and development during stressful conditions. However, the individual roles of Si and PGRs have extensively defined but their exquisite crosstalk with each other to mediate plant stress responses is still indiscernible. The present review is an upfront effort to delineate an intricate crosstalk/interaction between Si and PGRs to reduce abiotic stress adversities. The combined effects of interaction of Si with other signaling molecules such as reactive oxygen species (ROS), nitric oxide (NO) and calcium (Ca²⁺) for the survival of plants under stress and optimal conditions are also discussed.

Seed priming with gibberellic acid induces high salinity tolerance in Pisum sativum through antioxidants, secondary metabolites and up-regulation of antiporter genes

Salinity is one of the major abiotic stresses that limit productivity of pulse crops all over the world. Seed priming with phytohormone(s) is one of the most promising, authentic and cost-effective methods to mitigate the deleterious effect of salinity. The study was conducted to investigate potential of seed priming with gibberellic acid (GA3 ) to cope up with the adverse effects of salinity (0, 100, 200 and 300 mm NaCl) in pea (Pisum sativum L.) seedlings. There were different responses to salinity, which induced oxidative stress, higher accumulation of Na+ in shoots and roots and inhibition of photosynthetic traits. However, seed priming with GA3 showed promising effects on physiological traits under salinity stress and alleviated the adverse effects of salinity by inducing the antioxidant system, proline production, total phenol and flavonoid content and regulating ion homeostasis, along with up-regulation of Na+ /H+ antiporters (SOS1 and NHX1). Plants adapt and prevent high salt accumulation by inducing expression of Na+ /H+  antiporter (SOS1 and NHX1) proteins that enhance Na+ sequestration. Thus, seed priming with GA3 is important in alleviation of high salinity stress and can be used as a criterion for developing salt-tolerant cultivars.

Phosphorus supplementation modulates nitric oxide biosynthesis and stabilizes the defence system to improve arsenic stress tolerance in mustard

The interaction of mineral nutrients with metals/metalloids and signalling molecules is well known. In the present study, we investigated the effect of phosphorus (P) in mitigation of arsenic (As) stress in mustard (Brassica juncea L.). The study was conducted to investigate potential of 30 mg P·kg^-1 soil P supplement (diammonium phosphate) to cope up with the adverse effects of As stress (24 mg As·kg^-1 soil) in mustard plants Supplementation of P influenced nitric oxide (NO) generation, which up-regulated proline metabolism, ascorbate-glutathione system and glyoxalase system and alleviated the effects of on photosynthesis and growth. Arsenic stress generated ROS and methylglyoxal content was scavenged through P-mediated NO, and reduced As translocation from roots to leaves. The involvement of NO under P-mediated alleviation of As stress was substantiated with the use of cPTIO (NO biosynthesis inhibitor) and SNP (NO inducer). The reversal of P effects on photosynthesis under As stress with the use of cPTIO emphasized the role of P-mediated NO in mitigation of As stress and protection of photosynthesis The results suggested that P reversed As-induced oxidative stress by modulation of NO formation, which regulated antioxidant machinery. Thus, P-induced regulatory interaction between NO and reversal of As-induced oxidative stress for the protection of photosynthesis may be suggested for sustainable crops.

Zinc oxide nanoparticles (ZnO-NPs) induce salt tolerance by improving the antioxidant system and photosynthetic machinery in tomato

Zinc oxide nanoparticles (ZnO-NPs) has been demonstrated to positively regulate plant tolerance to multiple environmental stresses. However, till date little information has been gained regarding the role of ZnO-NPs in the salt stress regulation in plants. Hence, the objective of our study was to investigate the role of ZnO-NPs in the regulation of salt tolerance in tomato (Lycopersicon esculentum Mill.). In this regard, the tomato plants were subjected to salt stress by using NaCl (150 mM) at the time of transplantation [15 days after sowing (DAS)]. Foliar application of ZnO-NPs at different levels viz., 10, 50 and 100 mg/L in the presence/absence of NaCl (150 mM) was carried out at 25 DAS and sampling was done at 35 DAS. Results of our study revealed that foliar spray of ZnO-NPs significantly increased shoot length (SL) and root length (RL), biomass, leaf area, chlorophyll content and photosynthetic attributes of tomato plants in the presence/absence of salt stress. Besides, the application of ZnO-NPs mitigates the negative impacts of salt stress on tomato growth, and enhanced protein content and antioxidative enzyme activity such as peroxidase (POX), superoxide dismutase (SOD) and catalase (CAT) under salt stress. In conclusion, the ZnO-NPs plays an important role in the alleviation of NaCl toxicity in tomato plants. Hence, the ZnO-NPs can be used to boost the growth performance and mitigate the adverse effects caused by NaCl in tomato.

Application of Exogenous Protectants Mitigates Salt-Induced Na+ Toxicity and Sustains Cotton (Gossypium hirsutum L.) Seedling Growth: Comparison of Glycine Betaine and Salicylic Acid

Soil salinization adversely affects agricultural productivity. Mitigating the adverse effects of salinity represents a current major challenge for agricultural researchers worldwide. The effects of exogenously applied glycine betaine (GB) and salicylic acid (SA) on mitigating sodium toxicity and improving the growth of cotton seedlings subjected to salt stress remain unclear. The treatments in a phytotron included a control (CK, exogenously untreated, non-saline), two NaCl conditions (0 and 150 mM), four exogenous GB concentrations (0, 2.5, 5.0, and 7.5 mM), and four exogenous SA concentrations (0, 1.0, 1.5, and 2.0 mM). The shoot and roots exposed to 150 mM NaCl without supplementation had significantly higher Na+ and reduced K+, Ca2+, and Mg2+ contents, along with lowered biomass, compared with those of CK. Under NaCl stress, exogenous GB and SA at all concentrations substantially inversed these trends by improving ion uptake regulation and biomass accumulation compared with NaCl stress alone. Supplementation with 5.0 mM GB and with 1.0 mM SA under NaCl stress were the most effective conditions for mitigating Na+ toxicity and enhancing biomass accumulation. NaCl stress had a negative effect on plant growth parameters, including plant height, leaf area, leaf water potential, and total nitrogen (N) in the shoot and roots, which were improved by supplementation with 5.0 mM GB or 1.0 mM SA. Supplementation with 5.0 mM exogenous GB was more effective in controlling the percentage loss of conductivity (PLC) under NaCl stress.

Response of Olive Shoots to Salinity Stress Suggests the Involvement of Sulfur Metabolism

Global warming has two dangerous global consequences for agriculture: drought, due to water scarcity, and salinization, due to the prolonged use of water containing high concentrations of salts. Since the global climate is projected to continue to change over this century and beyond, choosing salt-tolerant plants could represent a potential paramount last resort for exploiting the secondary saline soils. Olive is considered moderately resistant to soil salinity as compared to other fruit trees, and in the present study, we investigated the influence of NaCl solutions (ranging from 0 to 200 mM) in a salt-tolerant (cv Canino) and two of its transgenic lines (Canino AT17-1 and Canino AT17-2), overexpressing tobacco osmotin gene, and in a salt-sensitive (Sirole) olive cultivar. After four weeks, most of the shoots of both Canino and Sirole plants showed stunted growth and ultimate leaf drop by exposure to salt-enriched media, contrary to transgenic lines, that did not show injuries and exhibited a normal growth rate. Malondialdehyde (MDA) content was also measured as an indicator of the lipid peroxidation level. To evaluate the role of the S assimilatory pathway in alleviating the adverse effects of salt stress, thiols levels as well as extractable activities of ATP sulfurylase (ATPS) and O-acetyl serine(thiol)lyase (OASTL), the first and the last enzyme of the S assimilation pathway, respectively, have been estimated. The results have clearly depicted that both transgenic lines overexpressing osmotin gene coped with increasing levels of NaCl by the induction of S metabolism, and particularly increase in OASTL activity closely paralleled changes of NaCl concentration. Linear correlation between salt stress and OASTL activity provides evidence that the S assimilation pathway plays a key role in adaptive response of olive plants under salt stress conditions.

Combined ability of salicylic acid and spermidine to mitigate the individual and interactive effects of drought and chromium stress in maize (Zea mays L.)

Application of the growth regulator salicylic acid (SA) and the polyamine spermidine (Spd) can be used to manage various plant abiotic stresses. We aimed to evaluate the sole and combined effects of SA and Spd on maize (Zea mays) under individual and combined drought and chromium (Cr) stress. Drought, Cr, and drought + Cr treatments caused oxidative stress by inducing higher production of reactive oxygen species (H₂O₂, O₂^-), enhanced malondialdehyde content and increased relative membrane permeability. Increased oxidative stress and higher Cr uptake in the host plant reduced the content of carotenoids, other photosynthetic pigments and protein, and changed carbohydrate metabolism. Combined drought + Cr stress was more damaging for the growth of maize plants than the individual stresses. Exogenous treatments of SA and Spd alleviated the adverse effects of drought and Cr toxicity, reflected by accumulations of osmolytes, antioxidants and endogenous polyamines. Single applications of Spd (0.1 mM) increased plant height, shoot fresh weight, leaf area, above-ground dry matter accumulation and polyamine content under drought, Cr, and drought + Cr stress conditions. However, the combined treatment SA + Spd (0.25 mM + 0.05 mM) was more effective in increasing protein and water contents, photosynthetic pigments, and carotenoids. The same treatment increased Cr tolerance in the maize plants by decreasing uptake of this heavy metal from root to shoot. The SA + Spd treatment also decreased oxidative stress by promoting antioxidant enzyme activities, and enhanced levels of proline, soluble sugars, and carbohydrate contents under individual and combined stress conditions. Results indicate that the combined half-dose application of SA + Spd may be utilized to boost the tolerance in maize under individual as well as combined drought and Cr stress conditions.

Transcriptome skimming of lentil (Lens culinaris Medikus) cultivars with contrast reaction to salt stress

Extensive transcriptomic skimming was conducted to decipher molecular, morphological, physiological, and biochemical responses in salt-tolerant (PDL-1) and salt-sensitive (L-4076) cultivars under control (0 mM NaCl) and salinity stress (120 mM NaCl) conditions at seedling stage. Morphological, physiological, and biochemical studies revealed that PDL-1 exhibited no salt injury and had higher K⁺/Na⁺ ratio, relative water content (RWC), chlorophyll, glycine betaine, and soluble sugars in leaves while lower H₂O₂ induced fluorescence signals in roots as compared to L-4076. Transcriptomic profile revealed a total of 17,433 significant differentially expressed genes (DEGs) under different treatments and cultivar combinations that include 2557 upregulated and 1533 downregulated transcripts between contrasting cultivars under salt stress. Accuracy of transcriptomic analysis was validated through quantification of 10 DEGs via quantitative real-time polymerase chain reaction (qRT-PCR). DEGs were functionally characterized by Gene Ontology (GO) analysis and assigned to various metabolic pathways using MapMan. DEGs were found to be significantly associated with phytohormone-mediated signal transduction, cellular redox homoeostasis, secondary metabolism, nitrogen metabolism, and cellular stress signaling. The present study revealed putative molecular mechanism of salinity tolerance in lentil together with identification of 5643 simple sequence repeats (SSRs) and 176,433 single nucleotide polymorphisms (SNPs) which can be utilized to enhance linkage maps density along with detection of quantitative trait loci (QTLs) associated with traits of interests. Stress-related pathways identified in this study divulged plant functioning that can be targeted to improve salinity stress tolerance in crop species.

Comparative Transcriptome Analysis of Two Contrasting Chinese Cabbage (Brassica rapa L.) Genotypes Reveals That Ion Homeostasis Is a Crucial Biological Pathway Involved in the Rapid Adaptive Response to Salt Stress

Salt is the most important limiting factor in plant yield and quality. Different Chinese cabbage cultivars appeared different salt tolerances, but there are few studies attempting to elucidate the mechanism underlying this phenomenon. In this study, 100 mmol L^-1 NaCl was found to be the most suitable treatment concentration according to a sprouting bag test of 39 Chinese cabbage cultivars, and through comprehensive comparison and analysis, the relative values of fresh weight and electrolyte leakage in leaves proved to be convenient indicators for the identification of salt tolerance in Chinese cabbage. We analyzed the physiological responses of Qinghua45 (salt-tolerant) and Biyuchunhua (salt-sensitive) in terms of the growth indexes, ion homeostasis and Photosynthesis, the results indicated that Qinghua45 could ensure osmotic regulation, ion homeostasis and photosynthesis under salt stress. Next, we compared the transcriptome dynamics of the two cultivars. Overall, 2,859 differentially expressed genes (DEGs) were identified, and the number of DEGs in Qinghua45 was significantly less than that in Biyuchunhua. VDAC promoted the release of Ca²⁺, which indirectly promoted the transport of Na⁺ to vacuoles through the SOS₂ pathway. Cation/H (+) antiporter 17 and V-H + -ATPase improve the exchange of Na⁺ and H⁺ and maintain Na⁺ in the vacuoles, thereby reducing the injury affected by salt stress. Increases in galactinol synthase and soluble protein synthesis helped relieve osmotic stress caused by salt, together, they regulated the Na⁺ content and chlorophyll biosynthesis of the plant and enabled the plant to adapt to salt stress over time.

Foliar-Applied Glutathione Mitigates Cadmium-Induced Oxidative Stress by Modulating Antioxidant-Scavenging, Redox-Regulating, and Hormone-Balancing Systems in Brassica napus

The antioxidant glutathione (GSH) mitigates adverse physio-metabolic effects and defends against abiotic types of stress, such as cadmium (Cd) stress. However, its function and role in resisting Cd phytotoxicity by leveraging plant antioxidant-scavenging, redox-regulating, and hormone-balancing systems have not been comprehensively and systematically demonstrated in the Cd-hyperaccumulating plant Brassica napus L. cv. Tammi (oilseed rape). In this study, the effects of exogenously applied GSH to the leaves of B. napus seedlings exposed to Cd (10 μM) were investigated. As a result, Cd stress alone significantly inhibited growth and increased the levels of reactive oxygen species (ROS) and the bioaccumulation of Cd in the seedlings compared with those in unstressed controls. Furthermore, Cd stress induced an imbalance in plant stress hormone levels and decreases in endogenous GSH levels and GSH redox ratios, which were correlated with reductions in ascorbate (AsA) and/or nicotinamide adenine dinucleotide phosphate (NADPH) redox states. However, the exogenous application of GSH to Cd-stressed B. napus seedlings reduced Cd-induced ROS levels and enhanced antioxidant-scavenging defenses and redox regulation by both increasing seedling AsA, GSH, and NADPH concentrations and rebalancing stress hormones, thereby enhancing Cd uptake and accumulation. These results demonstrate that GSH improved plant redox status by upregulating the AsA-GSH-NADPH cycle and reestablishing normal hormonal balance. This indicates that exogenously applied GSH can mitigate Cd phytotoxicity in B. napus and possibly other plants. Therefore, GSH can potentially be applied to Cd-polluted soil for plant remediation.

Silicon mediated improvement in the growth and ion homeostasis by decreasing Na+ uptake in maize (Zea mays L.) cultivars exposed to salinity stress

Silicon (Si), a major contributing constituent for plant resistance against abiotic stresses. In spite of this, the detailed mechanisms underlying the potential of Si in mitigating salt toxicity in maize (Zea mays L.) are still poorly understood. The present study deals with the response of Si application on growth, gaseous exchange, ion homeostasis and antioxidant enzyme activities in two maize cultivars (P1574 and Hycorn 11) grown under saline conditions. Salt stress remarkably reduced the plant tissue (roots and shoots) biomass, relative water contents (RWC), membrane stability index (MSI), gaseous exchange characteristics, and antioxidant enzymatic activities i.e., superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX) and catalase (CAT). However, salt-induced phytotoxicity increased the plant tissue concentration of malondialdehyde (MDA), hydrogen peroxide (H₂O₂), Na⁺/K⁺ ionic ratio, Na⁺ translocation (root to shoot), and its uptake. The detrimental effects were more prominent in Hycorn 11 cultivar than the P1574 cultivar at higher salinity level (S2; 160 mM NaCl). The addition of Si alleviated salt toxicity, which was more obvious in P1574 relative to Hycorn 11 as demonstrated by an increasing trend in RWC, MSI, and activities of SOD, POD, APX and CAT. Besides, Si-induced mitigation of salt stress was due to the depreciation in Na⁺/K⁺ ratio, Na⁺ ion uptake at the surface of maize roots, translocation in plant tissues and thereby significantly reduced Na⁺ ion accumulation. The findings showed a new dimension regarding the beneficial role of Si in maize plants grown under salt toxicity.

TaYS1A, a Yellow Stripe-Like Transporter Gene, Is Required for Wheat Resistance to Puccinia striiformis f. sp. Tritici

Yellow stripe-like (YSL) transporters are required for the transportation of metal-phytosiderophores and are structurally related to metal-nicotianamine complexes. Some studies also reported the involvement of YSL transporters in pathogen-induced defense. However, the molecular mechanisms of YSL genes involved in biotic stress responses are still not clear, especially in cereal crops. This study aimed to functionally characterize TaYS1A during the interaction of wheat and Puccinia striiformis f. sp. tritici (Pst), the causal agent of stripe rust disease. TaYS1A was localized in the cell membrane of wheat protoplasts and Nicotiana benthamiana cells. TaYS1A was significantly up-regulated in wheat leaves after being infected with the avirulent Pst isolate CYR23 and after treatment with salicylic acid (SA). Silencing of TaYS1A by the virus-induced gene silencing method enhanced the susceptibility of wheat to Pst accompanied by reducing the accumulation of SA and H2O2 and down-regulating the transcriptions of TaPR1 and TaPR2. In addition, TaYS1A was found to interact with TaNH2, a homolog of OsNH2, by yeast-two-hybrid assay, and silencing of TaYS1A diminished the expression of TaNH2. Our findings suggested the existence of positive regulation of TaYS1A in providing resistance against Pst by modulating SA-induced signaling and offered new insight into the biological role of YSL in wheat against pathogens.

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.

Salicylic acid mediated reduction in grain cadmium accumulation and amelioration of toxicity in Oryza sativa L. cv Bandana

Contamination of agricultural fields with Cadmium (Cd) due to several agricultural practices is increasing worldwide. The rice plants can easily take up Cd and accumulate it into different parts, including the grains, posing a threat to human health even at low concentration exposure. Several phytohormones, including Salicylic acid (SA) have been investigated since long for its alleviating properties under various biotic and abiotic stress conditions. In the present study, 100 μM SA application to ameliorate 25 μM Cd stress was studied for 72 h in hydroponics in Oryza sativa cv. Bandana seedlings. Pot experiments were done with same treatment condition and plants were grown till maturity. SA application to Cd exposed rice seedlings alleviated the stress condition, which was established by several physiological, biochemical, histochemical and gene expression analysis. SA treatment to Cd stressed seedlings showed elevated photosynthetic pigment content, on-protein thiol content and relieved the Cd induced growth inhibition considerably. It lowered the accumulation of ROS like, O2^- and H₂O₂ with a regulated antioxidative enzymatic activity. SA application in Cd exposed rice seedlings had upregulated expression of OsHMA3 and OsPCS1 whereasOsNRAMP2 gene was downregulated. Co-application of SA and Cd led to higher yield and improved agronomic traits in comparison to only Cd exposed plants under pot experimentation. Daily intake of Cd and Carcinogenic risk were also reduced by 99.75% and 99.99% respectively in the SA treated Cd stressed plants. SA positively affected the growth and tolerance of rice seedlings to Cd stress. Hence, SA addition to Cd contaminated soil can ensure rice cultivation without posing health risk to consumers.

Silver Nanoparticle Regulates Salt Tolerance in Wheat Through Changes in ABA Concentration, Ion Homeostasis, and Defense Systems

Salinity is major abiotic stress affecting crop yield, productivity and reduces the land-usage area for agricultural practices. The purpose of this study is to analyze the effect of green-synthesized silver nanoparticle (AgNP) on physiological traits of wheat (Triticum aestivum) under salinity stress. Using augmented and high-throughput characterization of synthesized AgNPs, this study investigated the proximity of AgNPs-induced coping effects under stressful cues by measuring the germination efficiency, oxidative-biomarkers, enzymatic and non-enzymatic antioxidants, proline and nitrogen metabolism, stomatal dynamics, and ABA content. Taken together, the study shows a promising approach in salt tolerance and suggests that mechanisms of inducing the salt tolerance depend on proline metabolism, ions accumulation, and defense mechanisms. This study ascertains the queries regarding the correlation between nanoparticles use and traditional agriculture methodology; also significantly facilitates to reach the goal of sustainable developments for increasing crop productivity via much safer and greener approachability.

Exogenous kinetin and putrescine synergistically mitigate salt stress in Luffa acutangula by modulating physiology and antioxidant defense

Salinity is one of the most vicious environmental constraints that hamper agricultural production. Experiments were done to explore the significant role of sole and synergistic supplementation of kinetin (100 µM KN) and putrescine (100 µM PUT) on Luffa acutangula in NaCl (100 mM) treatment. The harmful effects of salinity on growth were manifested by decreased seedling length, biomass, and pigment contents. We studied the effect of KN, and PUT in preventing salt (NaCl) induced physiological disorders and oxidative damages in 20-day-old Luffa acutangula seedlings. The individual application of KN and PUT increased growth and biochemical parameters, whereas combined KN + PUT treatment showed significant enhancement in growth, photosynthetic pigment content, and osmolyte accumulation in salt-affected plants. Application of KN and PUT also prevented hydrogen peroxide and superoxide production as confirmed by inhibition in electrolyte leakage and lipid peroxidation. Kinetin and PUT application upregulated the antioxidant defense system by enhancing antioxidant enzymes and non-enzymatic contents. Luffa seedlings treated with NaCl + KN + PUT showed 79, 26, 74, and 73% rise in superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase enzymes, respectively, in comparison to NaCl-stressed Luffa acutangula. Findings revealed that synergistic utilization of KN and PUT modulate growth and biochemical processes in seedlings efficaciously in comparison to the individual application under salt stress, and it may be due to a regulatory crosstalk mechanism.

Co-application of bio-fertilizer and salicylic acid improves growth, photosynthetic pigments and stress tolerance in wheat under drought stress

Drought stress hampers the growth and productivity of wheat crop worldwide. Thus far, different strategies have been proposed to improve drought tolerance in wheat but the combined application of plant growth-promoting rhizobacteria formulated bio-fertilizer (BF) and salicylic acid (SA) has not been thoroughly explored yet. Therefore, a pot experiment was conducted to observe the effect of SA, BF, and their combination on wheat plants under optimal and drought stress conditions. Seeds priming was done with BF (10⁷ CFU mL^-1). After 2 weeks of germination, SA (one mM) was applied as a foliar spray. Drought stress was applied by withholding water supply at three-leaf stage (30 d old plants) for the next 15 d until soil moisture dropped to 10%. Foliar application of SA increased the bacterial population of BF significantly compared to the sole application of BF under irrigated as well as drought stress conditions. Co-application of BF and foliar spray of SA induced drought tolerance in wheat plants by enhancing plant biomass, photosynthetic pigments, relative water content and osmolytes, and activities of the defense-related system. Plants treated with SA and BF together under drought stress had significantly increased leaf water status, Chl a, Chl b, and carotenoids synthesis by 238%, 125%, 167%, and 122%, respectively. Moreover, the co-application of SA and BF showed maximum SOD, POD, APX, and CAT activities by 165%, 85%, 156%, and 169% in the leaves while 153%, 86%, 116% and 200% in roots under drought stress. Similarly, the combined treatment exhibited a pronounced decrease in MDA content by 54% while increased production of proteins and proline by 145% and 149%, respectively. Our results showed that the co-application of SA and BF induced better drought tolerance as compared with the sole application of SA or BF. The results obtained herein suggest that combined application of BF and SA can be applied to the wheat crop to greatly improve drought tolerance in field conditions.

Negative effects of long-term moderate salinity and short-term drought stress on the photosynthetic performance of Hybrid Pennisetum

Plants are always suffering periods of soil water deficit and sustained soil salinity during their life cycle. Unraveling the mechanisms underpinning the responses of plants, especially the photosynthesis, to drought, salinity, and co-occurring stresses is critical for both the protection of natural vegetation and the stabilization of crop production. To better understand the downregulation of photosynthetic capability induced by soil salinity and drought, gas exchange parameters, leaf pigment contents, and chlorophyll (Chl) a fluorescence transients were analyzed in leaves of Hybrid Pennisetum. Our results showed that long-term moderate salinity, short-term drought, and the combination of these stressors decreased leaf pigment content by 11.4-31.5% and net photosynthetic rate (P_n) by 14.6-67.6% compared to those in untreated plants. The reduction of P_n in Hybrid Pennisetum under long-term salinity stress mainly occurred by stomatal limitation, whereas non-stomatal limitation played a dominant role under short-term drought stress. The changes in Chl a fluorescence kinetics (especially the appearance of the L-band and K-band) in both stress treatments showed that salinity and drought stress damaged the structural stability of photosystem II (PSII) and disturbed the equilibrium between the electrons at the acceptor and donor sides of PSII. Furthermore, although the negative effect of drought stress on leaf photosynthesis was much greater than that of salinity stress, moderate salt stress alleviated the negative effect of drought stress on the photosynthetic performance of Hybrid Pennisetum after long acclimation times.

Responses of ajowan (Trachyspermum ammi L.) to exogenous salicylic acid and iron oxide nanoparticles under salt stress

This research with a factorial arrangement was undertaken to investigate physiological responses of ajowan plants to foliar treatment of salicylic acid (1 mM) and nano-Fe₂O₃ (3 mM) under various salinity levels (0, 4, 8, 12 dS m^-1 NaCl, respectively). Rising salinity enhanced sodium and endogenous SA contents, soluble sugars, protein, glycine betaine, proline, antioxidant enzymes activities, ROS generation, and lipid peroxidation, while reduced potassium and iron contents, membrane stability index, leaf water content, leaf pigments, root and shoot biomasses, and seed yield. Application of particularly SA and SA+nano-Fe₂O₃ alleviated salt toxicity via enhancing K⁺ uptake, K⁺/Na⁺ ratio, Fe content, endogenous level of SA, the activities of antioxidant enzymes (superoxide dismutase, catalase, peroxidase, and polyphenol oxidase), and most of the osmolytes. These changes were resulted in improving membrane stability index, leaf water content, leaf pigments, root and shoot growth, and finally seed yield of plants under moderate and severe salinities. Therefore, these treatments can additively enhance salt tolerance and physiological performance of ajowan through increasing antioxidant capacity, osmolytes, and photosynthetic pigments. Graphical Abstract .

Responses of leaf gas exchange attributes, photosynthetic pigments and antioxidant enzymes in NaCl-stressed cotton (Gossypium hirsutum L.) seedlings to exogenous glycine betaine and salicylic acid

BACKGROUND

Application of exogenous glycine betaine (GB) and exogenous salicylic acid (SA) mitigates the adverse effects of salinity. Foliar spraying with exogenous GB or SA alleviates salt stress in plants by increasing leaf gas exchange and stimulating antioxidant enzyme activity. The effects of foliar application of exogenous GB and SA on the physiology and biochemistry of cotton seedlings subjected to salt stress remain unclear.

RESULTS

Results showed that salt stress of 150 mM NaCl significantly reduced leaf gas exchange and chlorophyll fluorescence and decreased photosynthetic pigment quantities and leaf relative water content. Foliar spray concentrations of 5.0 mM exogenous GB and 1.0 mM exogenous SA promoted gas exchange and fluorescence in cotton seedlings, increased quantities of chlorophyll pigments, and stimulated the antioxidant enzyme activity. The foliar spray also increased leaf relative water content and endogenous GB and SA content in comparison with the salt-stressed only control. Despite the salt-induced increase in antioxidant enzyme content, exogenous GB and SA in experimental concentrations significantly increased the activity of glutathione reductase, ascorbate peroxidase, superoxide dismutase, catalase and peroxidase, and decreased malondialdehyde content under salt stress. Across all experimental foliar spray GB and SA concentrations, the photochemical efficiency of photosystem II (FV/FM) reached a peak at a concentration of 5.0 mM GB. The net photosynthetic rate (Pn) and FV/FM were positively correlated with chlorophyll a and chlorophyll b content in response to foliar spraying of exogenous GB and SA under salt stress.

CONCLUSIONS

We concluded, from our results, that concentrations of 5.0 mM GB or 1.0 mM SA are optimal choices for mitigating NaCl-induced damage in cotton seedlings because they promote leaf photosynthesis, increase quantities of photosynthetic pigments, and stimulate antioxidant enzyme activity. Among, 5.0 mM GB and 1.0 mM SA, the best performance in enhancing endogenous GB and SA concentrations was obtained with the foliar application of 1.0 mM SA under salt stress.

Morpho-physiological and molecular responses of two Libyan bread wheat cultivars to plant growth regulators under salt stress

To study the effects of salt stress and plant growth regulators (kinetin, gibberellic acid, potassium) on growth, yield, glycine betaine content, phosphoenolpyruvate carboxylase (PEPC) and ribulose biphosphate carboxylase (RBC) gene expression of two Libyan bread wheat varieties, a factorial design of greenhouse experiment with three replications was conducted. Results revealed that salt stress significantly reduced plant growth and productivity of both varieties. Moreover, the addition of kinetin + potassium and gibberellic acid + potassium had improved the performance of the morpho-metric parameters of both genotypes under salt stress; but the performance was more effective for kinetin treatment than for gibberellic acid. At the biochemical level, the results showed that salt stress increased glycine betaine contents in both varieties with different proportions. This increase is more elevated in the presence of kinetin + potassium than the treatment with gibberellic acid+ potassium, which showed an almost similar result as in only salt stress. At the molecular level, the effects of salt stress and plant growth regulators on the PEPC and RBC gene expression showed that the increase was significantly higher for kinetin, gibberellic acid, and salt stress when compared to the control. Highlights - Salt stress reduced plant growth and productivity of bread wheat varieties. - Growth regulator improved the performance of the morphometric parameters. - The performance was more effective for kinetin treatment than for gibberellic acid. - Kinetin improved the glycine betaine gene expression more than gibberellic acid. - Kinetin increased significantly the phosphoenolpyruvate carboxylase and ribulose biphosphate carboxylase gene expression.

The role of salicylic acid and gibberellin signaling in plant responses to abiotic stress with an emphasis on heavy metals

Salicylic acid (SA) and gibberellins (GAs), as two important plant growth hormones, play a key role in increasing plant tolerance to abiotic stress. They contribute to the increased plant antioxidant activities in ROS scavenging, which is related to the enzymes involved in H₂O₂-detoxifying. In photosynthetic cycles, the endogenous form of these phytohormones enhances photosynthetic properties such as stomatal conductance, net photosynthesis (PN), photosynthetic oxygen evolution, and efficiency of carboxylation. Furthermore, in cell cycle, they are able to influence division and expansion of cell growth in plants under stress, leading to increased growth of radicle cells in a meristem, and ultimately contributing to the increased germination rate and lengths of shoot and root in the stress-affected plants. In the case of crosstalk between SA and GA, exogenous GA₃ can upregulate biosynthesis of SA and consequently result in rising levels of SA, enhancing plant defense response to environmental abiotic stresses. The aim of this paper was to investigate the mechanisms related to GA and SA phytohormones in amelioration of abiotic stress, in particular, heavy metal stress.