Salt Stress Environment Research Articles

Research Advances on Molecular Mechanism of Salt Tolerance in Suaeda.

Simple SummaryThis review comprehensively analyzes the molecular mechanism of Suaeda species under salt stress from aspects of physiology, biochemistry, transcriptomics, proteomics, and metabolomics, providing a theoretical basis for understanding the salt tolerance of Suaeda. The unique genetic and physiological characteristics of Suaeda support their high potential for utilization as promising biological resources to improve agriculture under saline conditions.Plant growth and development are inevitably affected by various environmental factors. High salinity is the main factor leading to the reduction of cultivated land area, which seriously affects the growth and yield of plants. The genus Suaeda is a kind of euhalophyte herb, with seedlings that grow rapidly in moderately saline environments and can even survive in conditions of extreme salinity. Its fresh branches can be used as vegetables and the seed oil is rich in unsaturated fatty acids, which has important economic value and usually grows in a saline environment. This paper reviews the progress of research in recent years into the salt tolerance of several Suaeda species (for example, S. salsa, S. japonica, S. glauca, S. corniculata), focusing on ion regulation and compartmentation, osmotic regulation of organic solutes, antioxidant regulation, plant hormones, photosynthetic systems, and omics (transcriptomics, proteomics, and metabolomics). It helps us to understand the salt tolerance mechanism of the genus Suaeda, and provides a theoretical foundation for effectively improving crop resistance to salt stress environments.

Scrutinizes the Sustainable Role of Halophilic Microbial Strains on Oxygen-Evolving Complex, Specific Energy Fluxes, Energy Flow and Nitrogen Assimilation of Sunflower Cultivars in a Suboptimal Environment.

Environmental extremes such as hypersaline conditions are significant threats to agricultural productivity. The sustainable use of halophilic microbial strains was evaluated in plant in a salt stress environment. Oxygen-evolving complex (OEC), energy compartmentalization, harvesting efficiencies (LHE), specific energy fluxes (SEF), and nitrogen assimilation of oilseed crops (Sunflower cultivars) in a suboptimal environment was examined. Plants were grown in a plastic pot (15 ×18 cm2) containing sterilized (autoclaved at 120°C for 1 h) soil. Twenty-five ml suspension (107 CFU/ml) each of Bacillus cereus strain KUB-15 and KUB-27 (accession number NR 074540.1) and Bacillus licheniformis strain AAB9 (accession number MW362506), were applied via drenching method. Month-old plants were subjected to salt stress via gradual increment method. The energy compartmentalization of microbial inoculated plants exposed to salt stress revealed higher photosystem II (PSII) activity at the donor side, lesser photo-inhibition, and increased performance of oxygen-evolving complex compared to control. High potassium (K+) and low sodium (Na+) ions in treated leaves with the activated barricade of the antioxidant system stimulated by Bacillus strains favored enhanced photochemical efficiency, smooth electron transport, and lesser energy dissipation in the stressed plants. Moreover, the results reveal the increased activity of nitrite reductase (NiR) and nitrate reductase (NR) by microbial inoculation that elevated the nitrogen availability in the salt-stressed plant. The current research concludes that the application of bio-inoculants that reside in the hyper-saline environment offers substantial potential to enhance salt tolerance in sunflowers by modulating their water uptake, chlorophyll, nitrogen metabolism, and better photochemical yield.

Role of Staphylococcus aureus Tet38 in Transport of Tetracycline and Its Regulation in a Salt Stress Environment.

Staphylococcus aureus Tet38 efflux pump has multiple functions, including conferring resistance to tetracycline and other compounds and enabling internalization and survival within epithelial cells. In this study, we evaluated the effects of sodium and potassium on tet38 expression. These monovalent cations are known to play a role in transport by the related S. aureus TetK and B. subtilis TetL transporters. tet38 transcription decreased with increasing sodium concentrations by means of direct repression by the salt stress-dependent KdpD/E regulator. tet38 transcription increased 20-fold and tetracycline minimum inhibitory concentration (MIC) increased 4-fold in a ΔkdpD mutant. KdpE bound specifically to the tet38 promoter. Under extreme salt stress, the survival of S. aureus with intact tet38 was reduced compared to that of a Δtet38 mutant. To study the effect of sodium on Tet38 function, we generated constructs overexpressing tet38 and tetK and introduced them into Escherichia coli TO114, which is deficient in major sodium transporters. Tet38 tetracycline efflux was directly demonstrated in a fluorescence assay, and tetracycline efflux of both Tet38 and TetK was abolished by the protonophore carbonyl cyanide 3-chlorophenylhydrazone (CCCP). In contrast, NaCl inhibited efflux by Tet38 but not TetK, whereas KCl inhibited efflux by TetK but not Tet38. Cell-associated Na increased with heterologous overexpression of Tet38. These data indicate that S. aureus Tet38 is a tetracycline efflux pump regulated by the KdpD/E regulator. Under salt stress, S. aureus adjusted its survival in part by reducing the expression of tet38 through KdpD/E. The mechanisms by which Tet38 is detrimental to salt tolerance in S. aureus and inhibited by sodium remain to be determined. IMPORTANCE This study shows that S. aureus Tet38 is a tetracycline efflux pump regulated by KdpD/E regulator. These findings are the first direct demonstration of Tet38-mediated tetracycline efflux, which had previously been inferred from its ability to confer tetracycline resistance. Under salt stress, S. aureus adjusts its survival in part by reducing the expression of tet38 through KdpD/E. We demonstrated the differences in the respective functions of S. aureus Tet38 and other tetracycline efflux transporters (S. aureus TetK, B. subtilis TetL) regarding their transport of tetracycline and Na+/K+. Notably, sodium selectively reduced tetracycline efflux by Tet38, and potassium selectively reduced tetracycline efflux by TetK. The multiple functions of Tet38 emphasize its importance in bacterial adaptation to and survival in diverse environments.

Study on the Relationship of Ions (Na, K, Ca) Absorption and Distribution to Photosynthetic Response of Salix matsudana Koidz Under Salt Stress.

To identify the key indicators for salt tolerance evaluation of Salix matsudana Koidz, we explored the relationship of ion absorption and distribution with chlorophyll, fluorescence parameters (leaf performance index, maximum photochemical efficiency), and photosynthetic gas parameters (net photosynthetic rate, transpiration, stomatal conductance, intercellular carbon dioxide concentration) under salt stress. We established 4 treatment groups and one control group based on salinity levels of NaCl hydroponic solutions (171, 342, 513, and 684 mm). The Na+/K+, Na+/Ca2+, chlorophyll fluorescence, and photosynthetic parameters of leaves were measured on the 1st, 3rd, 5th, 8th, 11th, and 15th days to analyze the correlations of chlorophyll, chlorophyll fluorescence and photosynthetic parameters to the ion distribution ratio. The results showed that (1) The ratio of the dry weight of roots to leaves gradually increased with increasing salt concentration, whereas the water content of leaves and roots first increased and then decreased with increasing time. (2) The content of Na+, Na+/K+, and Na+/Ca2+ in roots and leaves increased with increasing salt stress concentration and treatment time, and the difference gradually narrowed. (3) Ca2+ was lost more than K+ under salt stress, and Na+/Ca2+ was more sensitive to the salt stress environment than Na+/K+. (4) Because the root system had a retention effect, both Na+/K+ and Na+/Ca2+ in roots under different NaCl concentrations and different treatment times were higher than those in leaves, and Na+/Ca2+ was much higher than Na+/K+ in roots. (5) Na+/K+ had a higher correlation with fluorescence parameters than Na+/Ca2+. Among them, Na+/K+ had a significantly negative correlation with the maximum photochemical efficiency, and the correlation coefficient R2 was 0.8576. (6) Photosynthetic gas parameters had a higher correlation with Na+/Ca2+ than with Na+/K+. Among them, significantly negative correlations were noted between Na+/Ca2+ and Gs as well as between Na+/Ca2+ and E under salt stress. The correlation between Na+/Ca2+ and Gs was the highest with a correlation coefficient of 0.9368. (7) Na+/K+ and Na+/Ca2+ had no significant correlation with chlorophylls. Na+/Ca2+ was selected as a key index to evaluate the salt tolerance of S. matsudana Koidz, and the results provided a reference for analyzing the relationship between ion transport and distribution for photosynthesis.

SNP Based Trait Characterization Detects Genetically Important and Stable Multiple Stress Tolerance Rice Genotypes in Salt-Stress Environments.

Soil salinity is a major constraint to rice production in coastal areas around the globe, and modern high-yielding rice cultivars are more sensitive to high salt stress, which limits rice productivity. Traditional breeding programs find it challenging to develop stable salt-tolerant rice cultivars with other stress-tolerant for the saline environment in Bangladesh due to large yield variations caused by excessive salinity fluctuations during the dry (boro) season. We examined trait characterization of 18 advanced breeding lines using SNP genotyping and among them, we found line G6 (BR9621-B-1-2-11) (single breeding line with multiple-stress-tolerant QTL/genes) possessed 9 useful QTLs/genes, and two lines (G4:BR9620-2-7-1-1 and G14: IR 103854-8-3-AJY1) carried 7 QTLs/genes that control the desirable traits. To evaluate yield efficiency and stability of 18 rice breeding lines, two years of field experiment data were analyzed using AMMI (additive main effect and multiplicative interaction) and GGE (Genotype, Genotype Environment) biplot analysis. The AMMI analysis of variance demonstrated significant genotype, environment, and their interaction, accounting for 14.48%, 62.38%, and 19.70% of the total variation, respectively, and revealed that among the genotypes G1, G13, G14, G17, and G18 were shown to some extent promising. Genotype G13 (IR 104002-CMU 28-CMU 1-CMU 3) was the most stable yield based on the AMMI stability value. The GGE biplot analysis indicates 76% of the total variation (PC1 48.5% and PC2 27.5%) which is performed for revealing genotype × environment interactions. In the GGE biplot analysis, genotypes were checked thoroughly in two mega-environments (ME). Genotype G14 (IR103854-8-3-AJY1) was the winning genotype in ME I, whereas G1 (BR9627-1-3-1-10) in ME II. Because of the salinity and stability factors, as well as the highest averages of grain yield, the GGE and AMMI biplot model can explain that G1 and G13 are the best genotypes. These (G1, G6, G13, G14, G17, and G18) improved multiple-stress-tolerant breeding lines with stable grain yield could be included in the variety release system in Bangladesh and be used as elite donor parents for the future breeding program as well as for commercial purposes with sustainable production.

Salinity legacy: Foliar microbiome's history affects mutualist-conferred salinity tolerance.

The rapid human-driven changes in the environment during the Anthropocene have placed extreme stress on many plants and animals. Beneficial interactions with microorganisms may be crucial for ameliorating these stressors and facilitating the ecosystem services host organisms provide. Foliar endophytes, microorganisms that reside within leaves, are found in essentially all plants and can provide important benefits (e.g., enhanced drought tolerance or resistance to herbivory). However, it remains unclear how important the legacy effects of the abiotic stressors that select on these microbiomes are for affecting the degree of stress amelioration provided to their hosts. To elucidate foliar endophytes' role in host-plant salt tolerance, especially if salinity experienced in the field selects for endophytes that are better suited to improve the salt tolerance of their hosts, we combined field collections of 90 endophyte communities from 30 sites across the coastal Everglades with a manipulative growth experiment assessing endophyte inoculation effects on host-plant performance. Specifically, we grew >350 red mangrove (Rhizophora mangle) seedlings in a factorial design that manipulated the salinity environment the seedlings experienced (freshwater vs. saltwater), the introduction of field-collected endophytes (live vs. sterilized inoculum), and the legacy of salinity stress experienced by these introduced endophytes, ranging from no salt stress (0parts per thousand [ppt] salinity) to high salt stress (40 ppt) environments. We found that inoculation with field-collected endophytes significantly increased mangrove performance across almost all metrics examined (15%-20% increase on average), and these beneficial effects typically occurred when the endophytes were grown in saltwater. Importantly, our study revealed the novel result that endophyte-conferred salinity tolerance depended on microbiome salinity legacy in a key coastal foundation species. Salt-stressed mangroves inoculated with endophyte microbiomes from high-salinity environments performed, on average, as well as plants grown in low-stress freshwater, while endophytes from freshwater environments did not relieve host salinity stress. Given the increasing salinity stress imposed by sea level rise and the importance of foundation species like mangroves for ecosystem services, our results indicate that consideration of endophytic associations and their salinity legacy may be critical for the successful restoration and management of coastal habitats.

The Endophytic Strain ZS-3 Enhances Salt Tolerance in Arabidopsis thaliana by Regulating Photosynthesis, Osmotic Stress, and Ion Homeostasis and Inducing Systemic Tolerance.

Soil salinity is one of the main factors limiting agricultural development worldwide and has an adverse effect on plant growth and yield. To date, plant growth-promoting rhizobacteria (PGPR) are considered to be one of the most promising eco-friendly strategies for improving saline soils. The bacterium Bacillus megaterium ZS-3 is an excellent PGPR strain that induces growth promotion as well as biotic stress resistance and tolerance to abiotic stress in a broad range of host plants. In this study, the potential mechanisms of protection against salinity stress by B. megaterium ZS-3 in Arabidopsis thaliana were explored. Regulation by ZS-3 improved growth in A. thaliana under severe saline conditions. The results showed that ZS-3 treatment significantly increased the biomass, chlorophyll content and carotenoid content of A. thaliana. Compared to the control, the leaf area and total fresh weight of plants inoculated with ZS-3 increased by 245% and 271%, respectively; the chlorophyll a, chlorophyll b, and carotenoid contents increased by 335%, 146%, and 372%, respectively, under salt stress. Physiological and biochemical tests showed that ZS-3 regulated the content of osmotic substances in plants under salt stress. Compared to the control, the soluble sugar content of the ZS-3-treated group was significantly increased by 288%, while the proline content was significantly reduced by 41.43%. Quantification of Na+ and K+ contents showed that ZS-3 treatment significantly reduced Na+ accumulation and increased the K+/Na+ ratio in plants. ZS-3 also isolated Na+ in vesicles by upregulating NHX1 and AVP1 expression while limiting Na+ uptake by downregulating HKT1, which protected against Na+ toxicity. Higher levels of peroxidase and catalase activity and reduced glutathione were detected in plants inoculated with ZS-3 compared to those in uninoculated plants. In addition, it was revealed that ZS-3 activates salicylic acid (NPR1 and PR1) and jasmonic acid/ethylene (AOS, LOX2, PDF1.2, and ERF1) signaling pathways to induce systemic tolerance, thereby inducing salt tolerance in plants. In conclusion, the results of this study indicate that ZS-3 has the potential to act as an environmentally friendly salt tolerance inducer that can promote plant growth in salt-stressed environments.

Augmenting the Tolerance Potential of Muskmelon (Cucumis melo L.) Using Salicylic Acid

Salicylic acid (SA) is considered an important plant hormone that controls many aspects of plant growth and development, as well as resistance to biotic and abiotic stresses. In current investigations, a pot experiment consisting of four different levels of SA (0, 1, 2 and 3 mM SA) were tested on growth and physiological attributes of muskmelon (Cucumis melo L.), grown at different salinity levels (0, 50, 100 mM NaCl). Results revealed that all the morphological and physiological attributes were significantly (P<0.05) adversely affected by salinity stress, whereas application of SA improved growth rate of muskmelon both in saline and non-saline conditions. SA treated plants showed higher total chlorophyll content, photosynthetic rate and stomatal regulations as compared to control plants. SA application reduced the salt deleterious effects by inhibiting toxic Na+ ions accumulation in leaf and increased K+/Na+ ratio. Among the various applied concentrations, 2 mM SA increased shoot fresh weight by (30%), dry weight (34%), leaf area (25%) and K+/Na+ ratio by (84%) as compared to control plants. Thus, 2 mM SA concentration is concluded to be the best ameliorative treatment in salt stressed environments to enhance the muskmelon production.

Effect of zinc nanoparticles seed priming and foliar application on the growth and physio-biochemical indices of spinach (Spinacia oleracea L.) under salt stress.

Salt stress is the major risk to the seed germination and plant growth via affecting physiological and biochemical activities in plants. Zinc nanoparticles (ZnNPs) are emerged as a key agent in regulating the tolerance mechanism in plants under environmental stresses. However, the tolerance mechanisms which are regulated by ZnNPs in plants are still not fully understood. Therefore, the observation was planned to explore the role of ZnNPs (applied as priming and foliar) in reducing the harmful influence of sodium chloride (NaCl) stress on the development of spinach (Spinacia oleracea L.) plants. Varying concentrations of ZnNPs (0.1%, 0.2% & 0.3%) were employed to the spinach as seed priming and foliar, under control as well as salt stress environment. The alleviation of stress was observed in ZnNPs-applied spinach plants grown under salt stress, with a reduced rise in the concentration hydrogen peroxide, melondialdehyde and anthocyanin contents. A clear decline in soluble proteins, chlorophyll contents, ascorbic acid, sugars, and total phenolic contents was observed in stressed conditions. Exogenous ZnNPs suppressed the NaCl generated reduction in biochemical traits, and progress of spinach plants. However, ZnNPs spray at 0.3% followed by priming was the most prominent treatment in the accumulation of osmolytes and the production of antioxidant molecules in plants.

Cleaner production of proso millet (Panicum miliaceum L.) in salt-stressed environment using re-watering: From leaf structural alleviations to multi-omics responses

Severe environmental conditions inhibit plant growth, which is rapidly restored when conditions improve. However, the mechanisms underlying re-watering to relieve Na+ toxicity and promote growth in proso millet are unclear. Herein, comparative phenotypic, physiological, phytohormone and multi-omics analyses between salt-sensitive (SSR) and salt-tolerant (STIM) proso millet cultivars were performed under salt stress and subsequent re-watering. Phenotypic and physiological analyses suggested that the accumulation of biomass and growth rate of STIM were not only higher after stress recovery than SSR but also higher than its control condition (STIM_CK), showing a compensation effect. A microstructural analysis indicated that STIM maintained a better surface structure, internal structure, and chloroplasts after stress recovery compared with its reactions under salt stress. A phytohormone analysis showed that the jasmonic acid (JA) and jasmyl-L-isoleucine (JA-Ile) contents specifically and significantly increased in STIM under salt stress and recovered with re-watering. Transcriptome analysis suggested that 3160 differentially expressed genes (DEGs) (1671 DEGs were downregulated, and 1589 DEGs were upregulated) and 1319 DEGs (565 DEGs were downregulated, and 751 DEGs were upregulated) were specifically identified in STIM under salt stress and re-watering, respectively, whereas 6184 DEGs (2666 DEGs were downregulated, and 3518 DEGs were upregulated) and 2721 DEGs (1175 DEGs were downregulated, and 1546 DEGs were upregulated) were detected in SSR. Proteomes analyses showed that up to 38.28% and 44.68% of proteins were individually expressed specifically at the protein level in SSR under salt stress and subsequent re-watering, respectively, and 43.56% and 39.31% in STIM, respectively, indicating the involvement of posttranscriptional regulation under salt stress and subsequent re-watering. Subsequently, the functions of commonly regulated DEGs and differentially expressed proteins (DEPs) were analyzed, which were significantly enriched in photosynthesis and porphyrin and chlorophyll metabolism pathways. Therefore, this study provides guidelines for phytoremediation and utilization of saline soils, and cleaner crop production.

Profiling of energy compartmentalization in photosystem II (PSII), light harvesting complexes and specific energy fluxes of primed maize cultivar (P1429) under salt stress environment

Photosystem II efficiency is the most important aspect of stress physiology to keep photosynthetic momentum operative under stress conditions. In the last few decades effect of priming on the germination growth and physiology of plants were highlighted. Profiling energy compartmentalization in PSII using chlorophyll fluorescence kinetics and specific energy fluxes of primed seeds and plants has not been documented. It is crucial to discover the changes associated with the light-harvesting complexes, PSII functionality, and photochemical modulations occurring in the biochemical thylakoid membrane in response to priming and salt stress. The present study mainly focuses on photosystem II efficiency leading to physiological tolerance by seed priming. We grow the plants after seed priming with the solution of sodium chloride (75 and 150 mM), salicylic acid (1 and 2 mM), and calcium chloride (34 mM) and nitrate (20 mM). All the primed plants were subjected to salt stress 10 days after germination @ 0, 75, and 150 mM NaCl. Later germination, growth, morphology, physiology, PS II functionality and photochemical yield were evaluated. NaCl priming did more promising effects on energy compartmentalization, light-harvesting ability, and specific energy fluxes of photosystem II compared to salicylic acid and calcium salts under a stress environment. Maximum quantum yield (FV/FM), active reaction centers with higher efficiency of water splitting complex (FV/FO), restored electron flow, higher photochemical quenching (qP), oxygen evolution (SMT-phase), and almost negligible heat dissipation are associated with better osmotic adjustment and higher water uptake (RWC) under stress condition.

Effects of salt stress on the photosynthetic physiology and mineral ion absorption and distribution in white willow (Salix alba L.).

The purpose of this study was to explore the adaptive mechanism underlying the photosynthetic characteristics and the ion absorption and distribution of white willow (Salix alba L.) in a salt stress environment in cutting seedlings. The results lay a foundation for further understanding the distribution of sodium chloride and its effect on the photosynthetic system. A salt stress environment was simulated in a hydroponics system with different NaCl concentrations in one-year-old Salix alba L.branches as the test materials. Their growth, ion absorption, transport and distribution in the roots and leaves, and the changes in the photosynthetic fluorescence parameters were studied after 20 days under hydroponics. The results show that The germination and elongation of roots are promoted in the presence of 171mM NaCl, but root growth is comprehensively inhibited under increasing salt stress. Under salt stress, Na+ accumulates significantly in the roots and leaves, and the Na+ content and the Na+/K+ and Na+/Ca2+ root ratios are significantly greater than those in the leaves. When the NaCl concentration is ≤ 342mM, Salix alba can maintain relatively stable K+ and Ca2+ contents in its leaves by improving the selective absorption and accumulation of K+ and Ca2+ and adjusting the transport capacity of mineral ions to aboveground parts, while K+ and Ca2+ levels are clearly decreased under high salt stress. With increasing salt concentrations, the net photosynthetic rate (Pn), transpiration rate (E) and stomatal conductance (gs) of leaves decrease gradually overall, and the intercellular CO2 concentration (Ci) first decreases and then increases. When the NaCl concentration is < 342mM, the decrease in leaf Pn is primarily restricted by the stomata. When the NaCl concentration is > 342mM, the decrease in the Pn is largely inhibited by non-stomatal factors. Due to the salt stress environment, the OJIP curve (Rapid chlorophyll fluorescence) of Salix alba turns into an OKJIP curve. When the NaCl concentration is > 171mM, the fluorescence values of points I and P decrease significantly, which is accompanied by a clear inflection point (K). The quantum yield and energy distribution ratio of the PSⅡ reaction center change significantly (φPo, Ψo and φEo show an overall downward trend while φDo is promoted). The performance index and driving force (PIABS, PICSm and DFCSm) decrease significantly when the NaCl concentration is > 171mM, indicating that salt stress causes a partial inactivation of the PSII reaction center, and the functions of the donor side and the recipient side are damaged. The above results indicate that Salix alba can respond to salt stress by intercepting Na+ in the roots, improving the selective absorption of K+ and Ca2+ and the transport capacity to the above ground parts of the plant, and increasing φDo, thus shows an ability to self-regulate and adapt.

Effects of salt stress levels on nutritional quality and microorganisms of alfalfa-influenced soil.

BackgroundGlobally, there is a large amount of salinized land. These soils have varying degrees of salt stress, causing ionic toxicity and osmotic stress on plants. However, it is not clear how different degrees of salt stress affect plant nutrients and microbial communities. Thus, a comprehensive understanding of plant major nutrients and microbial communities response to salt stress is desirable.ResultsWe analyzed the main nutrients of the salt-tolerant ZhongMu No. 3 alfalfa variety planted in a salt stress environment. In mild and moderate group, the protein content and fatty acid content of alfalfa were the highest, indicating the best nutritional value. The severe group of salt stress affected the growth and development of alfalfa, as manifested by a decrease in the nutritional quality of alfalfa. Pseudomonas and Sphingobacterium that from alfalfa stem and leaf endophytes also increased with an increase in salt stress. In contrast, Sphingomonas, Methylobacterium, and Rhizobium decrease with increasing salt stress. Methylobacterium and Rhizobium have extremely significant differences in response to salt stress, and Exiquobacterium also shows significant differences.ConclusionsSoil salinity would be an important factor beyond which alfalfa nutrient quality and microbial community structure change. This study identified key levels of salt stress that may affect the nutrient quality and microbial community structure. These findings enhance our understanding of the effects of salt stress on the nutritional quality of alfalfa and provide a reference for the sustainable use of salinized soil in the future.

Characterization of Interactions between the Soybean Salt-Stress Responsive Membrane-Intrinsic Proteins GmPIP1 and GmPIP2

Salt tolerance is an important trait in soybean cultivation and breeding. Plant responses to salt stress include physiological and biochemical changes that affect the movement of water across the plasma membrane. Plasma membrane intrinsic proteins (PIPs) localize to the plasma membrane and regulate the water and solutes flow. In this study, quantitative real-time PCR and yeast two-hybridization were engaged to analyze the early gene expression profiles and interactions of a set of soybean PIPs (GmPIPs) in response to salt stress. A total of 20 GmPIPs-encoding genes had varied expression profiles after salt stress. Among them, 13 genes exhibited a downregulated expression pattern, including GmPIP1;6, the constitutive overexpression of which could improve soybean salt tolerance, and its close homologs GmPIP1;7 and 1;5. Three genes showed upregulated patterns, including the GmPIP1;6 close homolog GmPIP1;4, when four genes with earlier increased and then decreased expression patterns. GmPIP1;5 and GmPIP1;6 could both physically interact strongly with GmPIP2;2, GmPIP2;4, GmPIP2;6, GmPIP2;8, GmPIP2;9, GmPIP2;11, and GmPIP2;13. Definite interactions between GmPIP1;6 and GmPIP1;7 were detected and GmPIP2;9 performed homo-interaction. The interactions of GmPIP1;5 with GmPIP2;11 and 2;13, GmPIP1;6 with GmPIP2;9, 2;11 and GmPIP2;13, and GmPIP2;9 with itself were strengthened upon salt stress rather than osmotic stress. Taken together, we inferred that GmPIP1 type and GmPIP2 type could associate with each other to synergistically function in the plant cell; a salt-stress environment could promote part of their interactions. This result provided new clues to further understand the soybean PIP–isoform interactions, which lead to potentially functional homo- and heterotetramers for salt tolerance.

Evaluation of Multiple Salinity Tolerance Indices for Screening and Comparative Biochemical and Molecular Analysis of Pearl Millet [Pennisetum glaucum (L.) R. Br.] Genotypes

Salinity is a major constraint for plant growth, development and yield worldwide. Evaluation of a large number of germplasms in salt-stressed environments may help identify superior salt-tolerant genotypes. The present study dissects the genetic diversity of 33 pearl millet genotypes (landraces and inbred lines) for salinity tolerance through in vitro screening at the seedling stage. Our results revealed a significant reduction in total biomass and shoot growth of the salt-sensitive genotypes upon exposure to 150 mM NaCl, in contrast to the tolerant genotypes showing better growth characteristics. A significant differential effect of salt treatment on morphological traits was observed by analysis of variance (ANOVA), confirming substantial genetic diversity among all genotypes for salt tolerance. The genotypes were clustered into three groups based on multiple stress indices. The genotypes were also evaluated using principal component analysis (PCA) to identify the key contributing traits for stress tolerance. Based on these results, a total of four contrasting genotypes were selected for further biochemical and molecular analysis. Physiological studies confirmed that salt tolerance might be due to the higher content of osmolytes and the activity of antioxidant enzymes. Similarly, gene expression profiling of catalase (CAT), glutamate dehydrogenase (GDH), glutathione reductase (GR), and nitrate reductase (NR) revealed a profound increase in NR and GDH transcript levels in the tolerant genotypes, suggesting their major role as reactive oxygen species (ROS) scavengers under salinity. The overall findings of this study could be utilized further for candidate gene mining through “omics” approaches, aiming toward development of salinity resilient crop plants.

Genome-wide transcriptome analysis and physiological variation modulates gene regulatory networks acclimating salinity tolerance in chickpea

Salinity is a major abiotic stress that is a global threat to crop production, including chickpea. This study focused on understanding the complex molecular mechanisms underlying salinity tolerance using comparative transcriptome analysis of tolerant (ICCV 10, JG 11) and sensitive (DCP 92-3, Pusa 256) chickpea genotypes in control and salt-stressed environments. A total of 530 million reads were generated from root samples of four genotypes using Illumina HiSeq-2500. A total of 21,698 differentially expressed genes (DEGs) were identified, of which 11,456 and 10,242 were up- and down-regulated, respectively, in comparative analysis. These DEGs were associated with crucial metabolic pathways, including hormone signaling, photosynthesis, lipid and carbohydrate metabolism, and cell wall biogenesis. Gene ontology (GO) examination revealed an enrichment of transcripts involved in salinity response. A total of 4257 differentially expressed GO terms were categorized into 64 functional groups; of which, GO terms like, integral component of membrane, organelle, and cellular anatomical entity were highly represented in tolerant genotypes under salt stress. Significant up-regulation of transcripts encoding potassium transporter family HAK/KUP proteins, MIP/aquaporin protein family, NADH dehydrogenase, pectinesterase, and PP2C family proteins occurred under salt stress. The tolerant lines (ICCV 10 and JG 11) engaged highly efficient machinery in response to elevated salt stress, especially for signal transduction, transport and influx of K+ ions, and osmotic homeostasis. The overall study highlights the role of potential candidate genes and their regulatory networks which can be utilized in breeding salt tolerant chickpea cultivars.

Diversity and community structure of ectomycorrhizal fungi in Pinus thunbergii coastal forests bordering the Yellow Sea of China.

Ectomycorrhizas play a fundamental role in the function of forest ecosystems, being essential for plant nutrition absorption and soil quality. Many afforestation and reforestation programmes have begun to recover and maintain coastal forests in China, using pine species including Pinus thunbergii. We investigated the ectomycorrhizal colonization status of P. thunbergii in coastal pine forests of the Yellow Sea of China. We identified a total of 53 ectomycorrhizal fungal species in 74 soil samples collected from three sites and found that Thelephoraceae (10 spp.) and Russulaceae (8 spp.) were the most species-rich ectomycorrhizal fungal lineages. Russula sp. 1 was the most abundant species, accounting for 15.3% of the total ectomycorrhizal tips identified. Most of the remaining species were rare. At this small scale, host identity had no significant effect on the ectomycorrhizal fungal community composition (A = 0.036, P = 0.258), but sampling sites did (A = 0.135, P = 0.041). In addition, Na+ and K+ content and soil pH had significant effects on the ectomycorrhizal fungal community. The ectomycorrhizal fungal community associated with different host plants will become an important new direction for research, as ectomycorrhiza may have the potential to improve host capacity to establish in salt-stressed environments. This will provide a theoretical basis and technical support for saline soil reforestation and rehabilitation using pine species with compatible, native ectomycorrhizal fungi in Yellow Sea coastal areas.

Effect of co-inoculation with arbuscular mycorrhizal fungi and phosphate solubilizing fungi on nutrient uptake and photosynthesis of beach palm under salt stress environment

Beach plum (Prunus maritima) is an ornamental plant, famous for its strong salt and drought stress tolerance. However, the poor growth rate of transplanted seedlings has seriously restricted its application in salinized soil. This study investigated the effects of inoculation with arbuscular mycorrhizal fungus (AMF), Funneliformis mosseae, and phosphate-solubilizing fungus (PSF), Apophysomyces spartima, on the growth, nutrient (N, P, and K) uptake, and photosynthesis of beach plum under saline (170 mM NaCl) and non-saline (0 mM NaCl) conditions. We aimed to find measures to increase the growth rate of beach plum in saline-alkali land and to understand the reasons for this increase. The results showed that salinization adversely affected colonization by AMF but positively increased PSF populations (increased by 33.9–93.3% over non-NaCl treatment). The dual application of AMF and PSF mitigated the effects of salt stress on all growth parameters and nutrient uptake, significantly for roots (dry weight and P and N contents increased by 91.0%, 68.9%, and 40%, respectively, over non-NaCl treatment). Salinization caused significant reductions in net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (E), and intercellular CO2 concentration (Ci) value, while inoculation with AMF and PSF inoculations significantly abated such reductions. The maximum efficiency of photosystem II (PSII) (Fv/Fm), the photochemical quenching coefficient (qP), and the nonphotochemical quenching (NPQ) values were affected little by inoculation with AMF, PSF, or both under non-NaCl treatments. However, plants inoculated with AMF and/or PSF had higher Fv/Fm, qP, and ФPSII values (increased by 72.5–188.1%) than the control under NaCl treatment, but not a higher NPQ value. We concluded that inoculation with AMF or PSF increased nutrient uptake and improved the gas-exchange and Chl fluorescence parameters of beach plum under salt stress environment. These effects could be strengthened by the combination of AMF and PSF, especially for nutrient uptake, root growth, and Pn, thereby alleviating the deleterious effects of NaCl stress on beach plum growth.

Effect of Zataria multiflora Boiss. essential oil, NaCl, acid, time, and temperature on the growth of Listeria monocytogenes strains in broth and minced rainbow trout.

The small outbreaks of listeriosis as one of the leading causes of food poisoning‐associated deaths occur more than previously reported. In current study, the growth ability of Listeria monocytogenes strains isolated from different sources of food and human origin was measured under salt stress (0.5%, 2.5%, 5%, 7.5%, and 10%) and acid environments (pH = 6.64 and 5.77) for 96 hr by using a Bioscreen C microbiology reader at 37°C. In further steps of this study, after analysis of constituents of Zataria multiflora Boiss. essential oil (ZMEO), the sensory evaluation of the treated fish meat with ZMEO was performed. Then, the fish isolate of L. monocytogenes was exposed to sensory acceptable and subminimum inhibitory concentrations (subMICs) of ZMEO in fish broth and minced fish meat during incubation at abuse (12°C), room (22°C), and optimum (37°C) temperatures for 48 hr. The MIC of NaCl against four strains of L. monocytogenes was 10% at 37°C. The maximum optical densities (ODs) and under curve areas (AUC) of growth patterns in higher pH value and lower contents of NaCl followed the order of 21C > 6F > 66C > 22C of L. monocytogenes strains, while the lag time was prolonged in the reverse order. The maximum OD, growth, and lag times of samples treated with higher contents of NaCl and lower pH value were affected in a different order. The organoleptic evaluation showed that the fish meat treated with less than 0.5% of ZMEO was sensory acceptable. The population of L. monocytogenes remained relatively constant at the inoculation level of 107 cfu/ml (or g) at 12°C in broth and minced fish mediums. The inhibitory antilisterial activity of essential oil as an extensive‐used plant for food and pharmacological applications is negligible due to possible adverse sensory and toxic effects at relevant high doses.

Additive main effects and multiplicative interaction analyses of yield performance in rice genotypes for general and specific adaptation to salt stress in locations in India

The aim of this study was to identify stable rice genotypes tolerant to a salt stress environment and to identify ideal mega-environments using AMMI (additive main effects and multiplicative interaction) stability model analysis. A total of 13 rice genotypes and three salt tolerance checks were evaluated across 13 salt stress locations (alkaline and saline) for the two kharif seasons of 2014 and 2015. Genotype CSR 36 (CHK3) was found to be the most ideal of those tested. Genotypes CHK2 (CST 27) and IR 87952-1-1-1-2-3-B (G05) were found to be the most stable, with above average yields. The check CSR 36 (CHK3) genotype was the best performer in the majority of the environments studied, followed by CSR 27 (CHK2) and IR 87952-1-1-1-2-3-B (G05) which were the best genotypes in the mega-environment consisting of 21 environments evaluated across stress locations and year combinations. Overall, the most promising genotype (IR 87952-1-1-1-2-3-B) had high mean yield and stability and could be used for commercial cultivation or used as donor for breeding programs across salt-affected soils. The genotypes GN13 (IR 87938-1-1-2-1-3-B) and GN11 (IR 87938-1-2-2-1-3-B) showed 60–80% yield advantage at specific salt stress locations, showing that these genotypes could be used for specific environments of salt-affected soils in India.