Mechanisms Of Salinity Tolerance Research Articles

Chitosan-Induced Activation of the Antioxidant Defense System Counteracts the Adverse Effects of Salinity in Durum Wheat.

The present study was carried out with the aim of (i) evaluating the effect of chitosan (CTS) on the growth of durum wheat under salinity and (ii) examining CTS-regulated mechanisms of salinity tolerance associated with the antioxidant defense system. To achieve these goals, durum wheat seedlings were treated with CTS at different molecular weight, low (L-CTS, 50–190 kDa), medium (M-CTS, 190–310 kDa) and high (H-CTS, 310–375 kDa). The results obtained show that exposure to 200 mM NaCl reduced the shoot and the root dried biomass by 38% and 59%, respectively. The growth impairment induced by salinity was strongly correlated with an increase in the superoxide anion production (5-fold), hydrogen peroxide content (2-fold) and malondialdehyde (MDA) content (4-fold). Seedlings responded to the oxidative stress triggered by salinity with an increase in the total phenolic content (TPC), total flavonoid content (TFC) and total antioxidant activity (TAA) by 67%, 51% and 32%, respectively. A salt-induced increase in the activity of the antioxidant enzymes superoxide dismutase and catalase (CAT) of 89% and 86%, respectively, was also observed. Treatment of salt-stressed seedlings with exogenous CTS significantly promoted seedling growth, with the strongest effects observed for L-CTS and M-CTS, which increased the shoot biomass of stressed seedlings by 32% and 44%, respectively, whereas the root dried biomass increased by 87% and 64%, respectively. L-CTS and M-CTS treatments also decreased the superoxide anion production (57% and 59%, respectively), the hydrogen peroxide content (35% and 38%, respectively) and the MDA content (48% and 56%, respectively) and increased the TPC (23% and 14%, respectively), the TFC (19% and 10%, respectively), the TAA (up to 10% and 7%, respectively) and the CAT activity (29% and 20%, respectively). Overall, our findings indicate that CTS exerts its protective role against the oxidative damages induced by salinity by enhancing the antioxidant defense system. L-CTS and M-CTS were the most effective in alleviating the adverse effect of NaCl, thus demonstrating that the CTS action is strictly related to its molecular weight.

Morphological, physiological, and biochemical responses of Tunisian Urtica pilulifera L. under salt constraint

Urtica pilulifera from Urticaceae family was known by its benefit effects on human health and used in traditional medicine and recently largely used in pharmacological and food fields. In other hand, the salinization of soils is caused by several environmental factors leading to crop losses around the World. The ability of plants to tolerate salt stress is determined by multiple mechanisms. In the present study, morphological, physiological, and biochemical modulations in Urtica pilulifera under salt stress was evaluated to assess its tolerance or sensitization potential to salt stress using different concentrations of NaCl (0, 50, 100 and 150 mM). The studied parameters of Urtica pilulifera were evaluated by cultivating the plant on a hydroponic medium. Results showed that after 15 days of treatment, a reduction in plant growth was noted correlating with leaf chlorosis under 100 mM NaCl and an increased level of proline and soluble sugar. Regression analysis showed that the applied salt concentration was proportional with the activity of antioxidant enzymes including catalase (CAT), guaiacol peroxidase (GPX) and ascorbate peroxidase (APX), both on the arial and the root parts.Cellular damage induced by salinity is strongly correlated with the generation of reactive oxygen species, osmotic damage, and reduction in relative water content. Accelerated antioxidant activity and osmotic adjustment through training osmolytes, are effective salinity tolerance mechanisms developed by Urtica pilulifera.

Insights into the mechanisms of susceptibility and tolerance against salinity stress in rice plant

ABSTRACT
 Rice (Oryza sativa L.) is an important food crop that is consumed by more than half of the world's population. Soil salinity is a serious problem that reduces rice yield because it is more sensitive to salt stress than other cereal crops. Salinity affects many aspects of the rice plant phases like it has a damaging effect on rice plant growth e.g. germination inhibition, difficulties in the crop establishment, development of the leaf area, decrease in the production of the dry matter, delay in the seed setting and even leading to the sterility. The susceptibility or resistance to high salinity in rice plants is an organized activity of multiple genes which also interact with other components of the different path­ways of stress signals transduction. The salt tolerance genes can be used to produce salinity tolerant rice varieties by using genetic engineering and marker-assisted selection. In this review, we have discussed the effects of salt stress on different growth stages and yield of the rice plant and updated on different stress-responsive genes and salinity tolerance mechanisms which will be helpful to improve the high-yielding rice varieties against the salinity stress. To develop salt-tolerant and high-yielding rice varieties, we have focused on the need to incorporate genomics, phenotyping, and metabolic profiling into breeding and transgenic approaches.

Comparative analysis of responses to field salinity stress in contrasting soybean accessions highlights NaCl exclusion in leaves as a key mechanism for salinity stress tolerance.

Salinity is one of the main limitations to legume productivity in many regions of the world and it is estimated that 50% of all arable land will become affected by salinity by 2050. The impact of field salinity on soybean performance was assessed using two soybean accessions (KCW and HMC) cultivated in salt-treated soil and non-salt treated soil. We used a 30 cm deep field system layered with 0.4 kg/m2 NaCl for the salt-treated experiment while the control field received no salt treatment. The results show that salinity reduces soybean growth and yield as evident from the reduction in the plant shoot length, stem diameter, number of branches, number of pods and seed weight. However, the reduction in these growth parameters was less pronounced in the HMC accession than the KCW accession. Furthermore, Na+ content in leaves of the HMC accession was lower than that of the KCW accession. This proved that salinity has a damaging effect on soybean growth and yield and the relative tolerance of the HMC accession is attributed in part to its ability to restrict Na+ transport to the leaves. While the study emphasizes salt exclusion as a potentially useful mechanism for salinity tolerance in soybean, it provides evidence that the HMC accession is a good genetic resource for breeding soybean varieties with improved salinity stress tolerance.

Genome-Wide Association Mapping of Salinity Tolerance at the Seedling Stage in a Panel of Vietnamese Landraces Reveals New Valuable QTLs for Salinity Stress Tolerance Breeding in Rice.

Rice tolerance to salinity stress involves diverse and complementary mechanisms, such as the regulation of genome expression, activation of specific ion-transport systems to manage excess sodium at the cell or plant level, and anatomical changes that avoid sodium penetration into the inner tissues of the plant. These complementary mechanisms can act synergistically to improve salinity tolerance in the plant, which is then interesting in breeding programs to pyramidize complementary QTLs (quantitative trait loci), to improve salinity stress tolerance of the plant at different developmental stages and in different environments. This approach presupposes the identification of salinity tolerance QTLs associated with different mechanisms involved in salinity tolerance, which requires the greatest possible genetic diversity to be explored. To contribute to this goal, we screened an original panel of 179 Vietnamese rice landraces genotyped with 21,623 SNP markers for salinity stress tolerance under 100 mM NaCl treatment, at the seedling stage, with the aim of identifying new QTLs involved in the salinity stress tolerance via a genome-wide association study (GWAS). Nine salinity tolerance-related traits, including the salt injury score, chlorophyll and water content, and K+ and Na+ contents were measured in leaves. GWAS analysis allowed the identification of 26 QTLs. Interestingly, ten of them were associated with several different traits, which indicates that these QTLs act pleiotropically to control the different levels of plant responses to salinity stress. Twenty-one identified QTLs colocalized with known QTLs. Several genes within these QTLs have functions related to salinity stress tolerance and are mainly involved in gene regulation, signal transduction or hormone signaling. Our study provides promising QTLs for breeding programs to enhance salinity tolerance and identifies candidate genes that should be further functionally studied to better understand salinity tolerance mechanisms in rice.

Ion transporters and their molecular regulation mechanism in plants

With the global population predicted to grow by at least 25% by 2050, the need for sustainable production of nutritious foods is important for human and environmental health. Recent progress demonstrate that membrane transporters can be used to improve yields of staple crops, increase nutrient content and resistance to key stresses, including salinity, which in turn could expand available arable land. Exposure to salt stress affects plant water relations and creates ionic stress in the form of the cellular accumulation of Na+ and Cl- ions. However, salt stress also impacts heavily on the homeostasis of other ions such as Ca2+, K+, and NO3- and therefore requires insights into how transport and compartmentation of these nutrients are altered during salinity stress. Since Na+ interferes with K+ homeostasis, maintaining a balanced cytosolic Na+/K+ ratio has become a key salinity tolerance mechanism. Achieving this homeostatic balance requires the activity of Na+ and K+ transporters and/or channels. The aim of this review is to seek answers to this question by examining the role of major ions transporters and channels in ions uptake, translocation and intracellular homeostasis in plants.

Contrasting Responses of Guar Genotypes Shed Light on Multiple Component Traits of Salinity Tolerance Mechanisms

Guar (Cyamopsis tetragonoloba (L.) Taub.) is a legume crop, and gum derived from its seeds has various industrial applications. Due to its tolerance to various abiotic stresses, guar can be grown under water-deficit or high-salinity conditions. In this investigation, four diverse guar genotypes that performed at a similar level in field conditions were evaluated in a salinity experiment in the greenhouse lysimeter system. Based on the salt tolerance index (STI) for shoot biomass, root biomass, shoot length, and root length, Matador and PI 268229 were classified as salt-tolerant, and PI 340261 and PI 537281 as salt-sensitive. Leaf Na concentrations were 4- to 5.5-fold higher, and leaf Cl concentrations were 1.6- to 1.9-fold higher in salt-sensitive lines than salt-tolerant lines under salinity. The strong associations between the leaf K concentrations under salinity compared to the control (K-salinity/K-control) ratio and STI for stem and root length advocate higher importance of K-salinity/K-control than total leaf K concentrations. The expression analyses of genes involved in Na+ and Cl− transport revealed the importance of different component traits of salinity tolerance mechanisms, such as the exclusion of Na+/Cl− from the root, sequestration of Cl− in root vacuoles, retrieval of Na+/Cl− from xylem during salinity stress, root-to-shoot Na+/Cl− translocation, and K+-Na+ homeostasis.

Proteomic Investigations to Assess the Impact of Salinity on Vigna radiata L. Genotypes

Background: In our previous study, six cultivars of Mungo (Vigna radiata) were exposed to 100-250 mM NaCl and studied for changes in growth and biomass. Among them, AEM-96 cultivar of the Mung bean [Vigna radiata (L.) Wilczek cv.] was found to tolerate NaCl stress at 250 mM. Objective: The soluble proteome of salt-tolerant mungo cultivar (AEM-96) was compared to the proteome of control mungo to investigate the possible mechanism of salinity tolerance. Methods: Gel-based two-dimensional gel electrophoresis was employed for comparative proteomics. PDQuest-based image analysis of 2D SDS-PAGE was performed. Scatter plots were prepared and total spots were analyzed for 2-fold changes in abundance of protein spot intensities in control and treated gels. Results: In total 517 protein spots were detected; 36 with high significance. Among these 36 spots, 2-fold expression change was analyzed in 27 protein spots. Seven protein spots were upregulated, eight spots were down-regulated, 3 spots were newly induced and 9 spots were silenced, while 9 protein spots did not change their 2-fold abundance under salinity. Protein spots (9 in total) which were 2-fold upregulated and newly induced were excised from the respective gels. The spots were tryptically digested and run on LC-MS/MS for generating peptides and performing a comparative fingerprinting of the proteins. The peptide signal data was loaded on the Mascot (Swissprot) database to retrieve protein IDs. Proteins with the best score were selected, namely isomers of oxygen- evolving enhancer protein 1 (S1-S3), RuBisCO (S4), oxygen-evolving enhancer protein 2 (S5), Heat shock protein 70 isomers (S6-S7), RuBisCO activase (S8), rubber elongation factor (S9) and pathogen-related protein 10 (S10). Conclusion: The identified proteins were found to play important roles in photosynthesis, stress response and plant growth.

Raffinose accumulation and preferential allocation of carbon (14C) to developing leaves impart salinity tolerance in sugar beet

Sugar beet is a salt-tolerant crop that can be explored for crop production in degraded saline soils. Seeds of multigerm genotypes LKC-2006 (susceptible) and LKC-HB (tolerant) were grown in 150 mM NaCl, from germination to 60 days after sowing, to decipher the mechanism of salinity tolerance at the vegetative stage. The biomass of the root and leaf were maintained in the tolerant genotype, LKC-HB, under saline conditions. Na+ /K+ ratios were similar in roots and leaves of LKC-HB, with lower values under salinity compared to LKC 2006. Infrared temperatures were 0.96°C lower in LKC-HB than in LKC-2006, which helped regulate the leaf water status under stressed conditions. Pulse-chase experiment showed that 14 C photosynthate was preferentially allocated towards the development of new leaves in the tolerant genotype. The sugar profile of leaves and roots showed accumulation of raffinose in leaves of LKC-HB, indicating a plausible role in imparting salinity tolerance by serving as an osmolyte or scavenger. The molecular analysis of the genes responsible for raffinose synthesis revealed an 18-fold increase in the expression of BvRS2 in the tolerant genotype, suggesting its involvement in raffinose synthesis. Our study accentuated that raffinose accumulation in leaves is vital for inducing salinity tolerance and maintenance of shoot dry weight in sugar beet.

Comparative Phenotypic and Transcriptomic Analysis Reveals Key Responses of Upland Cotton to Salinity Stress During Postgermination.

To understand the molecular mechanisms of salinity tolerance during seed germination and post-germination stages, this study characterized phenotypic and transcriptome responses of two cotton cultivars during salinity stress. The two cultivars were salt-tolerant (ST) LMY37 and salt-sensitive (SS) ZM12, with the former exhibiting higher germination rate, growth, and primary-root fresh weight under salinity stress. Transcriptomic comparison revealed that up-regulation of differentially expressed genes (DEGs) was the main characteristic of transcriptional regulation in ST, while SS DEGs were mainly down-regulated. GO and KEGG analyses uncovered both common and specific responses in ST and SS. Common processes, such as reactive oxygen species (ROS) metabolism and cell wall biosynthesis, may be general responses to salinity in cotton. In contrast, DEGs involved in MAPK-signaling pathway activated by ROS, carotenoid biosynthesis pathway and cysteine and methionine metabolism pathway [producing the precursors of stress hormone abscisic acid (ABA) and ethylene (ET), respectively] as well as stress tolerance related transcription factor genes, showed significant expression differences between ST and SS. These differences might be the molecular basis leading to contrasting salinity tolerance. Silencing of GhERF12, an ethylene response factor gene, caused higher salinity sensitivity and increased ROS accumulation after salinity stress. In addition, peroxidase (POD) and superoxide dismutase (SOD) activity obviously declined after silencing GhERF12. These results suggest that GhERF12 is involved in salinity tolerance during early development. This study provides a novel and comprehensive perspective to understand key mechanisms of salinity tolerance and explores candidate genes that may be useful in developing stress-tolerant crops through biotechnology.

Evaluating and Screening of Agro-Physiological Indices for Salinity Stress Tolerance in Wheat at the Seedling Stage.

Soil salinity is a worldwide issue that affects wheat production. A comprehensive understanding of salt-tolerance mechanisms and the selection of reliable screening indices are crucial for breeding salt-tolerant wheat cultivars. In this study, 30 wheat genotypes (obtained from a rapid selection of 96 original varieties) were chosen to investigate the existing screening methods and clarify the salinity tolerance mechanisms in wheat. Ten-day-old seedlings were treated with 150 mM NaCl. Eighteen agronomic and physiological parameters were measured. The results indicated that the effects of salinity on the agronomic and physiological traits were significant. Salinity stress significantly decreased K+ content and K+/Na+ ratio in the whole plant, while the leaf K+/Na+ ratio was the strongest determinant of salinity tolerance and had a significantly positive correlation with salt tolerance. In contrast, salinity stress significantly increased Na+ concentration and relative gene expression (TaHKT1;5, TaSOS1, and TaAKT1-like). The Na+ transporter gene (TaHKT1;5) showed a significantly greater increase in expression than the K+ transporter gene (TaAKT1-like). We concluded that Na+ exclusion rather than K+ retention contributed to an optimal leaf K+/Na+ ratio. Furthermore, the present exploration revealed that, under salt stress, tolerant accessions had higher shoot water content, shoot dry weight and lower stomatal density, leaf sap osmolality, and a significantly negative correlation was observed between salt tolerance and stomatal density. This indicated that changes in stomata density may represent a fundamental mechanism by which a plant may optimize water productivity and maintain growth under saline conditions. Taken together, the leaf K+/Na+ ratio and stomatal density can be used as reliable screening indices for salt tolerance in wheat at the seedling stage.

The effect of salinity on the zinc(II) binding efficiency of siderophore functional groups and implications for salinity tolerance mechanisms in barley

The effect of salinity on the zinc(II) binding efficiency of siderophore functional groups and implications for salinity tolerance mechanisms in barley

Arbuscular Mycorrhizal Fungi Improve Growth, Physiological Status and Nutrients Accumulation of Ailanthus altissima Seedlings under Cadmium Pollution and Salinity

Arbuscular mycorrhizal fungi (AMF) are known to alleviate the undesirable effects of biotic and abiotic stresses on plants. The objective of this study was to assess the effect of AMF symbiosis on plant growth, physiology, and nutrients accumulation in leaves and roots of Ailanthus altissima (Mill.) Swingle under Cd and saline conditions. The pot experiment was carried out in factorial based on randomized complete block design (RCBD) with three replications. The treatments included salinity at three levels (non-saline water, 4 ds/m, and 8 ds/m), inoculation with AMF at two levels (uninoculation and Glomus mosseae inoculation) and cadmium (Cd) pollution at three levels (unpolluted soil, 15 mg Cd/kg soil, and 30 mg Cd/kg soil). The results revealed salinity and Cd pollution decreased plant height shoot and root biomass, but AMF increased them. The highest plant height, shoot and root biomass were observed at unpolluted and non-saline water. In contrast, the lowest plant growth was in uninoculated treatments with high salinity and Cd levels. Salinity increased proline content, CAT and SOD activities. Cd pollution did not change the proline concentration in the plants. The highest proline concentration and antioxidant enzyme (SOD and CAT) activities were observed in uninoculated plants with simultaneous application of high Cd and salt levels. Na+ accumulation in roots and leaves increased with salinity, but AMF decreased it. K+ content in leaves and roots decreased with Cd pollution and salinity and AMF increased it. Salinity and Cd pollution significantly accumulated high Cd in roots and leaves. Our work will widely improve the current knowledge of salinity and Cd tolerance mechanisms in tree species.

Comparative transcriptome and tolerance mechanism analysis in the two contrasting wheat (Triticum aestivum L.) cultivars in response to drought and salinity stresses

Drought and salinity are the two important and commonly co-occurring abiotic stresses affecting plant growth and productivity worldwide. Here, we compared the genome-wide transcriptome in the two contrasting wheat cultivars (JM22, drought/salt tolerant; YM20, salt sensitive) in response to drought (10% soil moisture) and salinity (100 mM NaCl) stresses. A total of 295 and 94 genes were characterized as drought and salinity responsive according to their different expression profile between JM22 and YM20 in response to drought and salinity stresses, respectively. Of these, 193 and 67 genes, up-regulated in JM22 while down-regulated/unchanged in YM20 and 103 and 27 genes unchanged in JM22 but down-regulated in YM20, under drought and salinity, respectively. Functional enrichment analysis showed that, JM22 recorded higher expression for genes related to ROS detoxification and defense, in response to drought (e.g. phenolic glucosidemalonyltransferase and anthocyanidin 5,3-O-glucosyltransferase-like) and salinity (flavonoid 3′-monooxygenase and heat shock 70 kDa protein). Meanwhile, genes encoding phytohormone and signal transduction (e.g. cytokinin, LRR receptor kinase and LRK14) were prominently up-regulated in JM22 under drought. F-type H+/Na+-transporting ATPase subunit beta, and Ca2+ signal transduction sensors and key regulatory genes responsible, including zinc finger, NAC and WRKY were showed higher expression in JM22 in salinity stress. Further analysis of genotypic difference in transcriptome in response to drought and salinity, we identified 10 DEGs, annotated to cellular process, metabolic process, osmotic regulation, and MAPK signaling pathway, being co-identified as drought and salinity tolerance associated DEGs. Our results suggest that the co-expression of these genes was important for tolerating and adapting to drought and salinity stresses in JM22. This finding increases our knowledge and understanding of the wheat drought and salinity tolerance mechanism and provides molecular bases in breeding potential under drought and salinity stresses.

Rhizosphere Engineering With Plant Growth-Promoting Microorganisms for Agriculture and Ecological Sustainability

The rhizosphere is undoubtedly the most complex microhabitat, comprised of an integrated network of plant roots, soil, and a diverse consortium of bacteria, fungi, eukaryotes, and archaea. The rhizosphere conditions have a direct impact on crop growth and yield. Nutrient-rich rhizosphere environments stimulate plant growth and yield and vice versa. Extensive cultivation exhaust most of the soils which need to be nurtured before or during the next crop. Chemical fertilizers are the major source of crop nutrients but their uncontrolled and widespread usage has posed a serious threat to the sustainability of agriculture and stability of an ecosystem. These chemicals are accumulated in the soil, drained in water, and emitted to the air where they persist for decades causing a serious threat to the overall ecosystem. Plant growth-promoting rhizobacteria (PGPR) present in the rhizosphere convert many plant-unavailable essential nutrients e.g., nitrogen, phosphorous, zinc, etc. into available forms. PGPR produces certain plant growth hormones (such as auxin, cytokinin, and gibberellin), cell lytic enzymes (chitinase, protease, hydrolases, etc.), secondary metabolites, and antibiotics, and stress alleviating compounds (e.g., 1-Aminocyclopropane-1- carboxylate deaminase), chelating agents (siderophores), and some signaling compounds (e.g., N-Acyl homoserine lactones) to interact with the beneficial or pathogenic counterparts in the rhizosphere. These multifarious activities of PGPR improve the soil structure, health, fertility, and functioning which directly or indirectly support plant growth under normal and stressed environments. Rhizosphere engineering with these PGPR has a wide-ranging application not only for crop fertilization but developing eco-friendly sustainable agriculture. Due to severe climate change effects on plants and rhizosphere biology, there is growing interest in stress-resilient PGPM and their subsequent application to induce stress (drought, salinity, and heat) tolerance mechanism in plants. This review describes the three components of rhizosphere engineering with an explicit focus on the broader perspective of PGPM that could facilitate rhizosphere engineering in selected hosts to serve as an efficient component for sustainable agriculture.

Salinity tolerance of <i>Avena sativa</i> fodder genotypes

Oats (Avena sativa L.) is an important winter season fodder cultivated in many parts of the world. India faces huge shortages of green forage and possesses large salt-affected areas, so identification of salt-tolerant material offers scope for breeding of cultivars for increasing production from salt-affected soils. Forty-eight genotypes of oats comprised of cultivars, germplasm accessions and advanced breeding lines were evaluated with the aim of identifying salt-tolerant genotypes for use on saline soils and/or in programs to breed more salt-tolerant cultivars. Screening was carried out at different growth stages in both pot and field studies. Germination and seedling vigor at different levels of salinity in terms of electrical conductivity (EC), i.e. EC4, EC8, EC12 and EC16, were assessed. Field-level salinity tolerance was assessed in pits where soils had EC ranging from 3.3 to 3.6 dS/m and pH 9.6. Sand culture experiments were carried out on 2 genotypes at different levels of NaCl solution as well as saline soil scrap solution so as to simulate a real field situation. Na, K, Ca and proline concentrations were estimated to understand the mechanism of salinity tolerance of the crop. The study resulted in identification of some suitable genotypes with acceptable levels of salt tolerance, which can be used in developing productive cultivars for saline soils.

Transcript Analysis of Two Spinach Cultivars Reveals the Complexity of Salt Tolerance Mechanisms

Increasing soil salinization threatens global crop productivity. An understanding of the genetic networks involved in salinity tolerance mechanisms of high-value crops, such as spinach, is lacking....

Water Uptake from Different Soil Depths for Desert Plants in Saline Lands of Dunhuang, NW China

Salinization is a major threat to the sustainability of land and water resources, especially in arid and semiarid regions. Understanding the water uptake from different soil depths for desert plants is useful for exploring salinity-tolerance mechanism in desert plants in extremely-arid and salinity-affected area. To understand water uptake from different soil depths for desert plants in Dunhuang, NW China, we used oxygen isotope composition in plant xylem water and soil water to determine the water sources in three different saline sites differing in their degree of soil electrical conductance (site 2 < site 1 < site 3). The co-existing desert plants in each saline site extracted different depth of soil water respectively: K. foliatum mainly used shallow soil water (0–20 cm); H. caspica and N. tangutorum mainly used deep soil water (40–200 cm); A. sparsifolia used water from the 120–200 cm soil layers, while T. ramosissima and E. angustifolia mainly extracted deeper soil water (>200 cm). Compared to that in saline site 2, Tamarix ramosissima and Alhagi sparsifolia can switch their water sources to deeper soil water when enduring more salt stress. Also, a significant and positive correlation between soil EC and soil water δ18O values was observed, indicating the evaporation would cause increase in salt concentration and isotopic enrichment in the upper soil profile. Overall, our results suggest that plants may explore deeper soil water to adapt to salt stress under severe salinity. This work may contribute to selecting salt-tolerant plants species which is vital to saline soil rehabilitation and utilization.

Recent progress in understanding salinity tolerance in plants: Story of Na+/K+ balance and beyond

High salt concentrations in the growing medium can severely affect the growth and development of plants. It is imperative to understand the different components of salt-tolerant network in plants in order to produce the salt-tolerant cultivars. High-affinity potassium transporter- and myelocytomatosis proteins have been shown to play a critical role for salinity tolerance through exclusion of sodium (Na+) ions from sensitive shoot tissues in plants. Numerous genes, that limit the uptake of salts from soil and their transport throughout the plant body, adjust the ionic and osmotic balance of cells in roots and shoots. In the present review, we have tried to provide a comprehensive report of major research advances on different mechanisms regulating plant tolerance to salinity stress at proteomics, metabolomics, genomics and transcriptomics levels. Along with the role of ionic homeostasis, a major focus was given on other salinity tolerance mechanisms in plants including osmoregulation and osmo-protection, cell wall remodeling and integrity, and plant antioxidative defense. Major proteins and genes expressed under salt-stressed conditions and their role in enhancing salinity tolerance in plants are discussed as well. Moreover, this manuscript identifies and highlights the key questions on plant salinity tolerance that remain to be discussed in the future.

Integrated analysis of transcriptomic and metabolomic data to evaluate responses to hypersalinity stress in the gill of the razor clam (Sinonovacula constricta)

Salinity is an important ecological factor that affects physiological metabolism, survival, and distribution of marine organisms. Despite changes in the osmolarity and composition of the cytosol during salinity shifts, marine mollusks are able to maintain their metabolic function. The razor clam (Sinonovacula constricta) survives the wide range of salinity in the intertidal zone via changes in behavior and physiology. To explore the stress responses and mechanisms of salinity tolerance in razor clams, we collected transcriptomic and metabolomic data from a control group (salinity 20‰, S20) and a salinity-stress group (salinity 35‰, S35). The transcriptome data showed that genes related to the immune system, cytoskeleton remodeling, and signal transduction pathways dominated in the S35 group to counteract hypersalinity stress in the gill. The metabolomic analysis showed that 142 metabolites were significantly different between the S35 and S20 groups and that amino acid and carbohydrate metabolism were affected by hypersalinity stress. Levels of amino acids and energy substances, such as l-proline, isoleucine, and fructose, were higher in the gill of the S35 group. The combination of transcriptomic and metabolomic data indicated that metabolism of amino acids, carbohydrates, and lipids was enhanced in the gill during adaptation to high salinity. These results clarified the complex physiological processes involved in the response to hyperosmotic stress and maintenance of metabolism in the gill of razor clams. These findings provide a reference for further study of the biological responses of euryhaline shellfish to hyperosmotic stress and a molecular basis for the search for populations with high salinity tolerance.