Improving Salinity Tolerance Research Articles

Hormesis management of Moringa oleifera with exogenous application of plant growth regulators under saline conditions

The study investigated the adaptability of Moringa oleifera to saline conditions, focusing on its hormesis behavior. It also examined how various plant growth regulators affected growth, physiological parameters, and bioactive compounds of moringa. In the first phase, different NaCl stress levels (0, 50, 100, 150, 200, and 250 mM) were applied. Notably, significant stimulation was observed at 100 mM stress for growth, total phenolics, total flavonoids and total chlorophyll content while 150 mM stress had a marked inhibitory effect, with survival decreasing at 200 and 250 mM NaCl levels. A 38% reduction in root attributes and shoot length, along with a 55% decrease in leaf score, was observed at 150 mM stress. Total phenolics showed a positive correlation with growth attributes. In the second phase, moringa plants grown under 50, 100, and 150 mM NaCl stress were treated with various plant growth regulators, including cytokinin (50 mg L−1), thiourea (5 mM), bezyl amino purine (BAP @50 mg L−1), salicylic acid (50 mg L−1), hydrogen peroxide (H2O2@120 μM), or ascorbic acid (50 mg L−1) to mitigate adverse effects of salinity. Cytokinin, BAP, and salicylic acid applications improved salinity tolerance, enhancing enzymatic, and non-enzymatic antioxidants, and the abundance of kaempferol, quercetin, hydroxybenzoic, and hydroxycinnamic acids. Pearson correlation and principal component analysis manifested relationships among growth parameters, antioxidant activities, flavonoids, and phenolic acids. This study provides new insights into hormesis management for moringa plants and the influence of plant growth regulators on flavonoids and phenolic acid levels in moringa leaves under saline conditions.

Enhancing Chickpea (Cicer arietinum L.) Tolerance to Salinity through Plant Growth Regulators

During the period of 2020-21, a research study was carried out at the Plant Protective Culture Unit within the semi-controlled environmental settings of the Bangladesh Agricultural Research Institute. The aim of the study was to mitigate the negative impacts of salinity stress on chickpea by applying various concentrations of salicylic acid (SA) and gibberellic acid (GA3). Plants were subjected to four different levels of salinity stress, including a control group, mild stress, moderate stress, and severe stress. This was achieved by irrigating them with four varying concentrations of saline water (5, 7.5, 10 and 12.5 dSm-1) starting from the 14th day after sowing (DAS) and continuing until maturity at 100 DAS. On the other hand, the control plants received regular irrigation with tap water. Two concentrations of salicylic acid (SA) specifically 200 ppm and 400 ppm, along with gibberellic acid (GA3) at 10 ppm and 20 ppm, were administered as a foliar spray once a week, commencing at 20 days after sowing (DAS) and continuing until the flowering stage. Data related to chlorophyll levels in the leaves and water-related traits, including relative water content (RWC) and water retention capacity (WRC) were collected seven days after the foliar spray of these plant growth regulators at the flowering stage. Additionally, measurements of total dry weight, yield, and various yield-contributing factors were taken at the point of maturity. The results indicated that chickpea suffered adverse consequences due to salinity stress which included a reduction in chlorophyll content, a decrease in relative water content, a decline in water retention capacity, a decrease in total dry weight and a lower overall yield. However, the foliar application of different doses of salicylic acid (SA) and gibberellic acid (GA3) under varying levels of salinity stress had beneficial effects in alleviating the impact of salinity stress. Interestingly, it was observed that lower concentrations of SA at 200 ppm and GA3 at 10 ppm were more effective in mitigating the adverse effects of salinity stress and improving salinity tolerance in chickpea, especially under mild salinity stress conditions (5 dSm-1) as evidenced by the positive influence on the parameters mentioned above.

How Does Zinc Improve Salinity Tolerance? Mechanisms and Future Prospects.

Salinity stress (SS) is a serious abiotic stress and a major constraint to agricultural productivity across the globe. High SS negatively affects plant growth and yield by altering soil physio-chemical properties and plant physiological, biochemical, and molecular processes. The application of micronutrients is considered an important practice to mitigate the adverse effects of SS. Zinc (Zn) is an important nutrient that plays an imperative role in plant growth, and it could also help alleviate the effects of salt stress. Zn application improves seed germination, seedling growth, water uptake, plant water relations, nutrient uptake, and nutrient homeostasis, therefore improving plant performance and saline conditions. Zn application also protects the photosynthetic apparatus from salinity-induced oxidative stress and improves stomata movement, chlorophyll synthesis, carbon fixation, and osmolytes and hormone accumulation. Moreover, Zn application also increases the synthesis of secondary metabolites and the expression of stress responsive genes and stimulates antioxidant activities to counter the toxic effects of salt stress. Therefore, to better understand the role of Zn in plants under SS, we have discussed the various mechanisms by which Zn induces salinity tolerance in plants. We have also identified diverse research gaps that must be filled in future research programs. The present review article will fill the knowledge gaps on the role of Zn in mitigating salinity stress. This review will also help readers to learn more about the role of Zn and will provide new suggestions on how this knowledge can be used to develop salt tolerance in plants by using Zn.

Physiological and lipidomic response of exogenous choline chloride alleviating salt stress injury in Kentucky bluegrass (Poa pratensis).

Choline participates in plant stress tolerance through glycine betaine (GB) and phospholipid metabolism. As a salt-sensitive turfgrass species, Kentucky bluegrass (Poa pratensis) is the main turfgrass species in cool-season areas. To improve salinity tolerance and investigate the effects of choline on the physiological and lipidomic responses of turfgrass plants under salinity stress conditions, exogenous choline chloride was applied to Kentucky bluegrass exposed to salt stress. From physiological indicators, exogenous choline chloride could alleviate salt stress injury in Kentucky bluegrass. Lipid analysis showed that exogenous choline chloride under salt-stress conditions remodeled the content of phospholipids, glycolipids, and lysophospholipids. Monogalactosyl diacylglycerol, digalactosyl diacylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and lysophosphatidylcholine content were increased and phosphatidic acid content were decreased in plants after exogenous choline chloride under salt treatment. Plant leaf choline content increased, but GB was not detected in exogenous choline chloride treatment plants under nonstress or salt-stress conditions. GB synthesis pathway related genes showed no clear change to choline chloride treatment, whereas cytidyldiphosphate-choline (CDP-choline) pathway genes were upregulated by choline chloride treatment. These results reveal that lipid remodeling through choline metabolism plays an important role in the salt tolerance mechanism of Kentucky bluegrass. Furthermore, the lipids selected in this study could serve as biomarkers for further improvement of salt-sensitive grass species.

Saline-Alkaline Stress Resistance of Cabernet Sauvignon Grapes Grafted on Different Rootstocks and Rootstock Combinations.

Grafting the wine grape variety Cabernet Sauvignon onto salinity-tolerant rootstocks can improve salinity tolerance and grape yields in regions with high salinity soils. In this experiment, the effects of different rootstocks and rootstock combinations on the saline-alkaline stress (modified Hoagland nutrient solution + 50 mmol L-1 (NaCl + NaHCO3)) of Cabernet Sauvignon were studied. Correlation and principal component analyses were conducted on several physiological indicators of saline-alkaline stress. Salinity limited biomass accumulation, induced damage to the plant membrane, reduced the chlorophyll content and photosynthetic capacity of plants, and increased the content of malondialdehyde, sodium (Na+)/potassium (K+) ratio, and antioxidant enzyme activities (superoxide dismutase, peroxidase, and catalase). Significant differences in several indicators were observed among the experimental groups. The results indicate that the saline-alkaline tolerance of Cabernet Sauvignon after grafting was the same as that of the rootstock, indicating that the increased resistance of Cabernet Sauvignon grapes to saline-alkaline stress stems from the transferability of the saline-alkaline stress resistance of the rootstock to the scion.

Overexpression of JsFLS5 in calli improves salinity tolerance by maintaining active oxygen balance and reducing Na+ toxicity in Juglans sigillata.

The escalating global climate change significantly threatens plant growth, development, and production through salinity stress. Flavonoids, a crucial category of secondary metabolites, have been extensively studied for their role in modulating plant growth and development mechanisms in the face of biological and abiotic stress. The flavonol synthetase (FLS) gene plays a key role in the biosynthesis and accumulation of flavonoids. To investigate the correlation between salt tolerance and flavonol synthesis, JsFLS5 was overexpressed in the callus of Juglans sigillata cv. "Qianhe-7." This study shows that the upregulation of JsFLS5 significantly elevates the overall flavonoid content by modulating the expression of genes associated with flavonoid synthesis under salinity stress conditions. Additionally, the overexpressing callus exhibited enhanced resistance to salt stress compared to the wild-type callus, as evidenced by reduced levels of reactive oxygen species accumulation, electrolyte leakage, and malondialdehyde content in the overexpressing callus relative to the wild type (WT). Moreover, the overexpressing callus showed higher antioxidant enzyme activity and a more efficient ascorbic acid-glutathione cycle. Furthermore, the concentration of Na+ in the overexpressing callus was lower than WT, resulting in a decreased Na+ /K+ ratio. These findings suggest that JsFLS5 overexpression in calli effectively mitigates the oxidative damage induced by osmotic stress and reduces Na+ toxicity by enhancing flavonoid synthesis under salt stress conditions. Consequently, this study offers a novel perspective for comprehending the role of JsFLS5 in the response to abiotic stress in J. sigillata.

Co-inoculation of Bacillus velezensis and Stenotrophomonas maltophilia strains improves growth and salinity tolerance in maize (Zea mays L.)

Limiting factors for plant growth, such as low nutrient availability and intolerance to high salinity, may impair the production of several crops. Plant growth-promoting bacteria (PGPB) present a potential solution to mitigate these limitations by stimulating plant growth and development. This study aimed to identify the strains LGMB12, LGMB319, and LGMB426 (Bacillus velezensis) and LGMB417 (Stenotrophomonas maltophilia), and to assess single and co-inoculation effects of these bacteria on the growth promotion of maize (Zea mays L.) plants under normal conditions and in high salinity environments. These strains were identified through Bayesian inference multilocus analysis using 16 S rRNA, gyrA, recA, and rpoB genes. Antibiosis analysis revealed that the strains did not inhibit each other's growth. Thirteen inoculation conditions were tested in greenhouse experiments including controls, inoculation of each strain separately and in the six pairs of combinations to evaluate growth promotion and salinity tolerance, using 75 and 100 mM NaCl in the irrigation water. The results revealed that co-inoculation yielded the best outcomes, highlighting the synergistic effects of combining the strains. Overall, this study emphasizes the potential of co-inoculation with Bacillus velezensis and Stenotrophomonas maltophilia strains as a strategy to enhance plant growth and improve salinity tolerance in maize cultivation. Further investigations are warranted to explore their application as bioinputs in agricultural settings.

Fulvic Acid Improves Salinity Tolerance of Rice Seedlings: Evidence from Phenotypic Performance, Relevant Phenolic Acids, and Momilactones.

Salinity is a severe stress that causes serious losses in rice production worldwide. This study, for the first time, investigated the effects of fulvic acid (FA) with various concentrations of 0.125, 0.25, 0.5, and 1.0 mL/L on the ability of three rice varieties, Koshihikari, Nipponbare, and Akitakomachi, to cope with a 10 dS/m salinity level. The results show that the T3 treatment (0.25 mL/L FA) is the most effective in stimulating the salinity tolerance of all three varieties by enhancing their growth performance. T3 also promotes phenolic accumulation in all three varieties. In particular, salicylic acid, a well-known salt-stress-resistant substance, is found to increase during salinity stress in Nipponbare and Akitakomachi treated with T3 by 88% and 60%, respectively, compared to crops receiving salinity treatment alone. Noticeably, the levels of momilactones A (MA) and B (MB) fall in salt-affected rice. However, their levels markedly rise in rice treated with T3 (by 50.49% and 32.20%, respectively, in Nipponbare, and by 67.76% and 47.27%, respectively, in Akitakomachi), compared to crops receiving salinity treatment alone. This implies that momilactone levels are proportional to rice tolerance against salinity. Our findings suggest that FA (0.25 mL/L) can effectively improve the salinity tolerance of rice seedlings even in the presence of a strong salt stress of 10 dS/m. Further studies on FA application in salt-affected rice fields should be conducted to confirm its practical implications.

Expression of triploid heterosis in the biomass productivity of energy willow plants under salinity stress

Bioenergy production from short rotation woody species grown on saline soil provides multiple environmental advantages. Breeding of energy willow for salinity tolerance can support green energy utilization. Here, we quantify triploid heterosis in biomass traits under salt stresses. Crosses between diploid cultivars (Tora and Inger) and our autotetraploid plants (PPE-2/6 and PPE-7) resulted in TH16/24 and TH21/2 triploid hybrid genotypes. Growth characteristics of shoots and roots of triploid hybrids and their parental plants were monitored by pixel-based phenotyping under high salt stress (NaCl 2.0 g kg −1/EC: 8.71 mS cm−1) in greenhouse. Different values of Mid-Parent Heterosis (MPH %) were recorded by comparing these two crossing combinations and top or above views (for TH16/24 plants: 3.66% (side pixels) and 22.25% (above pixels) and for TH21/2 plants: 63.30% (side pixels) and 72.10% (above pixels). At the end of the growing period, considerable MPH values were detected in biomass parameters of TH16/24 and TH21/2 plants (shoot length: 18.26%/26.28%; green biomass weight: 40.28%/52.40%; stem diameter: 15.40%/13.98%) in soil with 2.0 g NaCl kg−1. The TH21/2 hybrid plants expressed higher hybrid vigor than plants from the TH16/24 genotype. The TH21/2 hybrid plants exhibited better water use efficiency than their parental plants and showed high MPH values for K+/Na+ ratio in soil containing 2.0 g NaCl kg−1. The presented data support a conclusion that heterosis depending on crossing partners can ensure improvement in salinity tolerance for triploid hybrids. Field experiment has been initiated for the characterization of these hybrids under natural saline soil.

Allantoin improves salinity tolerance in Arabidopsis and rice through synergid activation of abscisic acid and brassinosteroid biosynthesis.

Soil salinity stress is one of the major bottlenecks for crop production. Although, allantoin is known to be involved in nitrogen metabolism in plants, yet several reports in recent time indicate its involvement in various abiotic stress responses including salinity stress. However, the detail mechanism of allantoin involvement in salinity stress tolerance in plants is not studied well. Moreover, we demonstrated the role of exogenous application of allantoin as well as increased concentration of endogenous allantoin in rendering salinity tolerance in rice and Arabidopsis respectively, via., induction of abscisic acid (ABA) and brassinosteroid (BR) biosynthesis pathways. Exogenous application of allantoin (10µM) provides salt-tolerance to salt-sensitive rice genotype (IR-29). Transcriptomic data after exogenous supplementation of allantoin under salinity stress showed induction of ABA (OsNCED1) and BR (Oscytochrome P450) biosynthesis genes in IR-29. Further, the key gene of allantoin biosynthesis pathway i.e., urate oxidase of the halophytic species Oryza coarctata was also found to induce ABA and BR biosynthesis genes when over-expressed in transgenic Arabidopsis. Thus, indicating that ABA and BR biosynthesis pathways were involved in allantoin mediated salinity tolerance in both rice and Arabidopsis. Additionally, it has been found that several physio-chemical parameters such as biomass, Na+/K+ ratio, MDA, soluble sugar, proline, allantoin and chlorophyll contents were also associated with the allantoin-mediated salinity tolerance in urate oxidase overexpressed lines of Arabidopsis. These findings depicted the functional conservation of allantoin for salinity tolerance in both plant clades.

Sett priming with salicylic acid improves salinity tolerance of sugarcane (Saccharum officinarum L.) during early stages of crop development

Sugarcane (Saccharum officinarum L.), a globally cultivated carbohydrate producing crop of industrial importance is being challenged by soil salinity due to its glycophytic nature. Water stress coupled with cellular and metabolic alterations resulting from excess sodium (Na+) ion accumulation is irreversibly damaging during early crop developmental stages that often results in complete crop failure. This study therefore aimed to explore the potential of salicylic acid as a sett priming material to mitigate the negative effects of salt stress on sugarcane during germination and early growth stages. Five doses of salicylic acid (0 [hydropriming] [control], 0.5 mM, 1 mM, 1.5 mM and 2 mM) were tested against three levels of salinity (0.5 dS m−1 [control], 4 dS m−1, and 8 dS m−1) within a polyhouse environment. Results revealed 11.2%, 18.5%, 25.4%, and 38.6%, average increase in final germination, germination energy, seedling length and seedling vigor index respectively with a subsequent reduction of 21% mean germination time. Investigations during early seedling growth revealed 21.6%, 17.5%, 27.0%, 39.9%, 10.7%, 11.5%, 17.5%, 47.9%, 35.3% and 20.5% overall increase in plant height, total leaf area, shoot dry matter, root dry matter, leaf greenness, relative water content, membrane stability index, proline content, total antioxidant activity and potassium (K+) ion accumulation respectively with a subsequent reduction of 24.9% Na+ ion accumulation and 35.8% Na+/K+ ratio due to salicylic acid priming. Germination, seedling growth and recovery of physiochemical traits were highly satisfactory in primed setts than non-primed ones even under 8 dS m−1 salinity level. This study should provide useful information for strategizing salinity management approaches for better productivity of sugarcane.

Humic Acid Modulates Ionic Homeostasis, Osmolytes Content, and Antioxidant Defense to Improve Salt Tolerance in Rice.

The sensitivity of rice plants to salinity is a major challenge for rice growth and productivity in the salt-affected lands. Priming rice seeds in biostimulants with stress-alleviating potential is an effective strategy to improve salinity tolerance in rice. However, the mechanisms of action of these compounds are not fully understood. Herein, the impact of priming rice seeds (cv. Giza 179) with 100 mg/L of humic acid on growth and its underlaying physiological processes under increased magnitudes of salinity (EC = 0.55, 3.40, 6.77, 8.00 mS/cm) during the critical reproductive stage was investigated. Our results indicated that salinity significantly reduced Giza 179 growth indices, which were associated with the accumulation of toxic levels of Na+ in shoots and roots, a reduction in the K+ and K+/Na+ ratio in shoots and roots, induced buildup of malondialdehyde, electrolyte leakage, and an accumulation of total soluble sugars, sucrose, proline, and enzymic and non-enzymic antioxidants. Humic acid application significantly increased growth of the Giza 179 plants under non-saline conditions. It also substantially enhanced growth of the salinity-stressed Giza 179 plants even at 8.00 mS/cm. Such humic acid ameliorating effects were associated with maintaining ionic homeostasis, appropriate osmolytes content, and an efficient antioxidant defense system. Our results highlight the potential role of humic acid in enhancing salt tolerance in Giza 179.

The Efficiency of Humic Acid for Improving Salinity Tolerance in Salt Sensitive Rice (Oryza sativa): Growth Responses and Physiological Mechanisms

High-yielding rice cultivars exhibit a great performance in non-saline fields; however, their growth and productivity are greatly reduced in salt-affected lands. Humic acid has a promising stress-mitigating potential and can be effective in improving salt tolerance in salinity sensitive rice cultivars. Herein, seeds of Giza 177 (high-yielding but salt-sensitive rice cultivar) were primed in 40 mg/l humic acid, sown, and maintained. Then growth and physiological responses of the humic acid-primed plants to increased levels of salinity (EC: 0.55, 3.40, 6.77, and 8.00 mS/cm) were evaluated at the reproductive stage. Increasing salinity induced a progressive retardation in plant height, leaf area, fresh and dry weights. Such retardation was associated with Na+ buildup in shoot and root, high electrolyte leakage and accumulation of malondialdehyde, total soluble sugars, sucrose, glucose, proline, total soluble proteins, flavonoids, and phenolics. In contrast, salinity reduced K+, K+/Na+ ratio, total carbohydrates, and the activity of catalase, peroxidase, and polyphenol oxidase. Humic acid enhanced growth under non-saline and saline conditions. The humic acid-induced improvement in salt tolerance was associated with the reduction of Na+ toxicity, increasing K+/Na+ ratio, regulating osmolytes concentration, and enhancing the activities of antioxidant enzymes and thus reduce the oxidative stress. These results indicate that humic acid successfully reduced the salinity-induced plant damage, improved metabolism, and maintained active growth of Giza 177 under saline irrigation.

The biochar-based nanocomposites improve seedling emergence and growth of dill by changing phytohormones and sugar signaling under salinity

Biochar-based nanocomposites (BNCs) with a high level of sodium sorption capacity may improve salinity tolerance and seedling establishment of dill. Thus, a pot experiment was conducted to evaluate the effects of solid biochar (30 g solid biochar kg-1 soil) and biochar-based nanocomposites of iron (BNC-FeO) and zinc (BNC-ZnO) in individual (30 g BNC kg-1 soil) and a combined form (15 g BNC-FeO + 15 g BNC-ZnO kg-1 soil) on dill seedling growth in different levels of salt stress (non-saline, 6 and 12 dSm-1). Salinity caused a decrease in emergence percentage and emergence rate of seedlings. Increasing salinity of soil up to 12 dSm-1 decreased the biomass of dill seedlings by about 77%. Application of biochar and particularly BNCs increased the content of potassium, calcium, magnesium, iron, and zinc, reducing and non-reducing sugars, total sugars, invertase and sucrose synthase activities, leaf water content, gibberellic acid, and indole-3-acetic acid in dill plants, leading to an improvement in seedling growth (shoot length, root length, and dry weight) under saline conditions. Sodium content was noticeably decreased by BNC treatments (9-21%), which reduced mean emergence rate and stress phytohormones such as abscisic acid (31-43%), jasmonic acid (21-42%), and salicylic acid (16-23%). Therefore, BNCs especially in combined form can potentially improve emergence and growth of dill seedlings under salt stress, through reducing sodium content and endogenous stress hormones, and enhancing sugars and growth promoting hormones.

Interplay between membrane proteins and membrane protein-lipid pertaining to plant salinity stress.

High salinity in agricultural lands is one of the predominant issues limiting agricultural yields. Plants have developed several mechanisms to withstand salinity stress, but the mechanisms are not effective enough for most crops to prevent and persist the salinity stress. Plant salt tolerance pathways involve membrane proteins that have a crucial role in sensing and mitigating salinity stress. Due to a strategic location interfacing two distinct cellular environments, membrane proteins can be considered checkpoints to the salt tolerance pathways in plants. Related membrane proteins functions include ion homeostasis, osmosensing or ion sensing, signal transduction, redox homeostasis, and small molecule transport. Therefore, modulating plant membrane proteins' function, expression, and distribution can improve plant salt tolerance. This review discusses the membrane protein-protein and protein-lipid interactions related to plant salinity stress. It will also highlight the finding of membrane protein-lipid interactions from the context of recent structural evidence. Finally, the importance of membrane protein-protein and protein-lipid interaction is discussed, and a future perspective on studying the membrane protein-protein and protein-lipid interactions to develop strategies for improving salinity tolerance is proposed.

Physiological Role of Arbuscular Mycorrhizae and Vitamin B1 on Productivity and Physio-Biochemical Traits of White Lupine (Lupinus termis L.) Under Salt Stress

AbstractArbuscular mycorrhizalfungi (AMF) have a key role in natural and agricultural ecosystems affecting plant nutrition, soil biological activity and modifying the availability of nutrients. Thiamine (Vitamin B1) is an essential coenzyme which incorporated in a wide range of plant metabolic processes. Thus, this research aimed to study the possibility of mitigating the negative effect of salinity stress on white lupine plant via using AMF and Vit B1through assessment growth, various physiological traits and yield components of the white lupine plant. AMF was added to the soil (0.0 and 7 g pot−1) and Vit B1was foliar applied to white lupine seedlings (0.0, 100 and 200 mgL−1) and watered by two levels of salinity (0.0 or 5000 mgL−1). Salinity stress (5000 mgL−1) resulted in significant reductions in growth photosynthetic pigments constituents, endogenous indole acetic acid (IAA), some elements & productivity of white lupine in comparison to control plants. While, increasing phenols, some osmolytes and sodium compared to control (plants irrigated by tap water). Adding AMF to soil with the recommended dose boosted white lupine growth, certain physiological aspects and productivity in white lupine plants under irrigation with saltwater (5000 mgL−1). Furthermore, exogenous Vit B1 treatment with 100 & 200 mgL−1not only enhanced growth and seeds productivity of white lupine plants under normal irrigation but also, improved salinity tolerance by increasing white lupine growth and productivity via inmproving photosynthetic pigments, osmolytes levels and element contents compared to their corresponding controls. Finally it could be concluded that, 200 mgL−1Vit B1 wit AMF treatment shows superiority in inducing maximum improving white lupine plant salinity tolerance.

Improvement of Salinity Tolerance in Water-Saving and Drought-Resistance Rice (WDR)

Rice is one of the most economically important staple food crops in the world. Soil salinization and drought seriously restrict sustainable rice production. Drought aggravates the degree of soil salinization, and, at the same time, increased soil salinity also inhibits water absorption, resulting in physiological drought stress. Salt tolerance in rice is a complex quantitative trait controlled by multiple genes. This review presents and discusses the recent research developments on salt stress impact on rice growth, rice salt tolerance mechanisms, the identification and selection of salt-tolerant rice resources, and strategies to improve rice salt tolerance. In recent years, the increased cultivation of water-saving and drought-resistance rice (WDR) has shown great application potential in alleviating the water resource crisis and ensuring food and ecological security. Here, we present an innovative germplasm selection strategy of salt-tolerant WDR, using a population that is developed by recurrent selection based on dominant genic male sterility. We aim to provide a reference for efficient genetic improvement and germplasm innovation of complex traits (drought and salt tolerance) that can be translated into breeding all economically important cereal crops.

Nitric oxide, calmodulin and calcium protein kinase interactions in the response of Brassica napus to salinity stress.

Involvement of nitric oxide (NO) in plant metabolism and its connection with phytohormones has not been fully described, thus information about the role of this molecule in signalling pathways remains fragmented. In this study, the effects of NO on calmodulin (CAM), calcium protein kinase (CPK), content of phytohormones and secondary metabolites in canola plants under salinity stress were investigated. We applied 100 μM sodium nitroprusside as an NO source to canola plants grown under saline (100 mM NaCl) and non-saline conditions at the vegetative stage. Plant growth was negatively affected by salinity, but exogenous NO treatment improved growth. NO caused a significant increase in activity of CAT, SOD and POX through their enhanced gene expression in stressed canola. Salinity-responsive genes, namely CAM and CPK, were induced by NO in plants grown under salinity. NO application enhanced phenolic compounds, such as gallic acid and coumaric acid and flavonoid compound,s catechin, diadzein and kaempferol, in plants subjected to salinity. NO treatment enhanced abscisic acid and brassinosteroids but decreased auxin and gibberellin in stressed canola plants. The impacts of NO in improving stress tolerance in canola required CAM and CPK. Also, NO signalling re-established the phytohormone balance and resulted in enhanced tolerance to salt stress. Furthermore, NO improved salinity tolerance in canola by increasing enzymatic and non-enzymatic antioxidant content.

B-type response regulator hst1 controls salinity tolerance in rice by regulating transcription factors and antioxidant mechanisms

Salinity is a serious environmental problem that limits plant yield in almost half of the agricultural fields. The hitomebore salt tolerant 1(hst1) is a mutant B-type response regulator gene that was reported to improve salinity tolerance in the ‘YNU31-2-4' (YNU) genotype. The sister line (SL) is salt-sensitive, and the nearest genomic relative of the YNU plant has the OsRR22 gene, which is the non-mutant form of the hst1 gene. Biochemical and comprehensive transcriptome analysis of SL and YNU plants was performed to clarify the salinity tolerance mechanism(s) mediated by the hst1 gene. The hst1 gene reduced Na+ ions, lipid peroxidation, and H2O2 content, and improve proline and antioxidant enzymes activities under salt stress. Various transporter and gene-specific transcriptional regulator genes up-regulated in presence of the hst1 gene under saline conditions, identifying that post-stress transcription factors (OsbHLH056, OsH43, OsGRAS29, and OsMADS1) contributed to improved salinity tolerance in YNU plants. Specifically, OsSalT, miR156, and OsLPT1.16 genes were up-regulated, while upstream (OsHKs and OsHPs) and downstream regulators of the OsRR22 gene were down-regulated in YNU plants under saline conditions. Notably, the transcription factors reprogramming, upstream and downstream genes, indicate that these pathways are transcriptionally regulated by the hst1 gene. The findings of the regulatory role of the hst1 gene on plant transcriptome provide a greater understanding of hst1–mediated salt tolerance in rice plants. This knowledge will contribute to understanding the salinity tolerance mechanisms in rice and the evolution of salt-tolerant crops with the ability to withstand higher salinity to ensure food security during climate change.

Soil Salinity is a Serious Environmental Threat to Plant Diseases- A review

The rise in sea level, which causes an increase in salinity in both surface and ground water systems, is among the resultant effects of global climate change. Soil salinity is one of the notable environmental factors contributing to infectious plant diseases. Stress due to soil salinity affects plant tolerance to biotic stress by attenuating their immunity to pathogens leading to prevention of defence genes expression, reduced antioxidant activity and weakening of defence signalling proteins. The pathogen virulence and pathogenicity as well as an enhancement of pathogen development and multiplication are all influenced by soil salinity. Restriction of water absorption, toxic ion build up in plant tissues, nutrient deficiency, hormonal and metabolic imbalance, oxidative stress as physiological effects of salt stress, significantly affect the degree and occurrence of plant diseases. Thus, level of soil salinity is directly proportional to the severity and incidence of plant diseases. Controlling the effect of salinity by improving salinity tolerance in plants and deployment of salinity control measures will provide a long lasting solution on its effect on plant diseases. This will also serve as an approach to plant economic disease control.