Alkali-salt Stress Research Articles

Epichloë endophytes improved Leymus chinensis tolerance to both neutral and alkali salt stresses.

Symbiotic relationships with microbes may influence how plants respond to environmental change. In the present study, we tested the hypothesis that symbiosis with the endophytes promoted salt tolerance of the native grass. In the field pot experiment we compared the performance of endophyte-infected (E+) and endophyte-uninfected (E-) Leymus chinensis, a dominant species native to the Inner Mongolia steppe, under altered neutral and alkaline salt stresses. The results showed that under both neutral and alkaline salt stresses, endophyte infection significantly increased plant height, leaf length and fibrous root biomass. Under neutral salt stress, endophyte infection decreased Na+ content and Na+/K+ ratio (p=0.066) in the leaf sheath while increased Ca2+ and Mg2+ content in the rhizome. Under alkali salt stress, endophyte infection tended to increase K+ content in the fibrous root, enhance Mg2+ content in the fibrous root while reduce Na+/K+ ratio in the leaf blade in the 100 mmol/L alkali salt treatment. Although endophyte-infected L. chinensis cannot accumulate Na+ high enough to be halophytes, the observed growth promotion and stress tolerance give endophyte/plant associations the potential to be a model for endophyte-assisted phytoremediation of saline-alkaline soils.

Identification of Alkaline Salt Tolerance Genes in Brassica napus L. by Transcriptome Analysis.

Soil salt alkalization is one major abiotic factor reducing the productivity of crops, including rapeseed, an indispensable oil crop and vegetable. The mechanism studies of alkali salt tolerance can help breed highly resistant varieties. In the current study, rapeseed (B. napus) line 2205 exhibited more tolerance to alkaline salt than line 1423 did. In line 2205, the lesser plasma membrane damage index, the accumulated osmotic solute, and higher antioxidant enzyme activities contributed to alkaline tolerance. A more integrated mesophyll-cell structure was revealed under alkali salt stress by ultrastructure observation in line 2205, which also implied a lesser injury. Transcriptome analysis showed that more genes responded to alkaline salt in line 2205. The expression of specific-response genes in line 1423 was lower than in line 2205. However, most of the specific-response genes in line 2205 had higher expression, which was mainly enriched in carbohydrate metabolism, photosynthetic processes, ROS regulating, and response to salt stress. It can be seen that the tolerance to alkaline salt is attributed to the high expression of some genes in these pathways. Based on these, twelve cross-differentially expressed genes were proposed as candidates. They provide clues for further analysis of the resistance mechanism of rapeseed.

Resistance of highland barley seedlings to alkaline salt and freeze-thaw stress with the addition of potassium fulvic acid

Crops are commonly subjected to freeze-thaw and salt stress factors simultaneously in Qinghai-Tibet Plateau. In the agricultural field, potassium fulvic acid can not only promote plant growth and increase crop yield but also enhance plant resistance to stress. In this study, the changes of osmotic adjustment substances, antioxidant enzyme activities and photosynthetic characteristics of barley seedlings under alkaline salt and freeze-thaw stress were investigated by laboratory simulation. The results showed that under single alkaline salt stress, the soluble protein content increased significantly (P < 0.05), and the malondialdehyde (MDA) content of seedlings increased by 63.1%; however, antioxidant enzymes activities and photosynthetic rate of barley seedlings decreased. Under combined stresses of alkaline salt and freeze-thaw, the soluble protein content, antioxidant enzyme activities, and photosynthetic rate of barley seedlings decreased; in contrast, the MDA content of seedlings increased. With the addition of potassium fulvic acid, the soluble protein content of seedlings increased, MDA content decreased significantly (P < 0.05), and enzyme activities tended to be stable. This study revealed that the addition of a proper amount of potassium fulvic acid could mitigate the damage of alkali salt and freeze-thaw stress on barley seedlings.

Alkali salt stress causes fast leaf apoplastic alkalinization together with shifts in ion and metabolite composition and transcription of key genes during the early adaptive response of Vicia faba L

The mechanisms by which plants respond to alkali salt stress are still obscure, and the relevance of alkaline pH under combined alkali salt stress. Early stress responses can indicate mechanisms leading to damage and plant resistance. The apoplast contains essential determinants for plant growth, specifically early apoplastic pH fluctuations are induced by many stressors and hypothesized to be involved in stress signalling. Hence, this study aims to identify fast responses specific to alkaline pH and alkali salt stress by exposing the root of hydroponically grown Vicia faba L. plants to 150 min of either 50 mM NaHCO3 (pH 9) treatment or alkaline pH 9 alone. Apoplastic pH was monitored in real-time by ratiometric fluorescence microscopy simultaneously with SWIR transmission-based measurements of leaf water content (LWC). Moreover, we examined the effect of these stresses on apoplastic, symplastic and xylem ion and metabolite composition together with transcriptions of certain stress-responsive genes. Physiological and transcriptional changes were observed in response to NaHCO3 but not to alkaline pH alone. NaHCO3 elicited a transient reduction in LWC, followed by a transient alkalinization of the apoplast and stomatal closure. Simultaneously, organic acids and sugars accumulated. Fast upregulation of stress-responsive genes showed the significance of gene regulation for early plant adaptation to alkali salt stress.

Early growth reduction in Vicia faba L. under alkali salt stress is mainly caused by excess bicarbonate and related to citrate and malate over accumulation

Rather than high pH or Na+, excess bicarbonate, by inducing over-accumulation of organic acids (through dark fixation) in plant roots, was hypothesized to be the main growth-limiting factor under alkali salt stress. Thus, the effect of four treatments viz. control (pH 6.0), high pH (9.0), high pH (9.0) plus sodium sulfate (25 mM) and sodium bicarbonate (50 mM, pH 9.0) on growth, gas exchange and leaf water content, organic acid accumulation, ion relations, oxidative damage and changes in the expression of key genes was investigated in Vicia faba. The bicarbonate treatment showed the highest growth reduction, PEPCase gene expression and accumulation of citrate and malate in roots. Bicarbonate treated plants preferentially accumulated Fe2+ and Ca2+ in roots and reduced root exudation of citrate and malate. Moreover, these plants experienced K+ and Ca2+ deficiencies, which caused a massive increase in H2O2 concentration in leaves and roots, leading to severe oxidative damage. Bicarbonate treated plants showed reduced levels of PM H+-ATPase, SOS1, CS, and MDH gene expression in roots. The cascade of events confirms the hypothesized central role of organic acid accumulation in bicarbonate induced stress, making bicarbonate more detrimental to plant growth than high pH or its combination with sodium salt.

Genetic regulatory networks for salt-alkali stress in Gossypium hirsutum with differing morphological characteristics

BackgroundCotton grows in altering environments that are often unfavorable or stressful for its growth and development. Consequently, the plant must cope with abiotic stresses such as soil salinity, drought, and excessive temperatures. Alkali-salt stress response remains a cumbersome biological process and is regulated via a multifaceted transcriptional regulatory network in cotton.ResultsTo discover the molecular mechanisms of alkali-salt stress response in cotton, a comprehensive transcriptome analysis was carried out after alkali-salt stress treatment in three accessions of Gossypium hirsutum with contrasting phenotype. Expression level analysis proved that alkali-salt stress response presented significant stage-specific and tissue-specific. GO enrichment analysis typically suggested that signal transduction process involved in salt-alkali stress response at SS3 and SS12 stages in leaf; carbohydrate metabolic process and oxidation-reduction process involved in SS48 stages in leaf; the oxidation-reduction process involved at all three phases in the root. The Co-expression analysis suggested a potential GhSOS3/GhCBL10-SOS2 network was involved in salt-alkali stress response. Furthermore, Salt-alkali sensitivity was increased in GhSOS3 and GhCBL10 Virus-induced Gene Silencing (VIGS) plants.ConclusionThe findings may facilitate to elucidate the underlying mechanisms of alkali-salt stress response and provide an available resource to scrutinize the role of candidate genes and signaling pathway governing alkali-salt stress response.

Influences of Soda Soil on the Ultrastructure and Storage Inclusions of Chloroplasts of <i>Syringa oblata</i> Lindl.

With a high pH value, soda soil restricts the growth of plants. It had previously been assumed that the inhibition of plant growth by neutral salt stress was partly due to the changes of the ultrastructure and storage inclusions of chloroplasts. The aim of this paper is to investigate the effects of alkali-salt mixed stress of soda soil on chloroplasts of higher plant Syringa oblata Lindl. Testing S. oblata plants had grown for more than five years in soda soil, and transmission electron microscope was used for determining the ultrastructure and storage inclusions of chloroplasts. The results showed that some chloroplasts were destroyed, the normal chloroplasts became smaller, and the envelopes of the functional chloroplasts were slightly expanded generally in soda-stressed plants. The most noteworthy fact was that much more starchgrains accumulated in the chloroplasts of S. oblata growing in soda soil than in neutral soil. The total contents of plastoglobules in chloroplasts did not change considerably, and plastoglobules with different electron densities appeared in chloroplasts in the plants growing in soda soil. We presume that the reduction of the volume and number of functional chloroplasts and the occupation of carbon resources by starch grains accumulated in chloroplasts were the possible reasons for the inhibition of S. oblata growth by soda soil. The accumulation of starch grains was one of the adaptive traits of S. oblata, which promoted the survival of plants in soda soil for that the starch grains could serve as a steady source of soluble sugars, which were known as protectors of plant cells under stressed conditions. Soda soil did not significantly change the total content of plastoglobules in chloroplasts, but changed their compositions.

Antioxidant metabolism variation associated with alkali-salt tolerance in thirty switchgrass (Panicum virgatum) lines.

Soil salinization is a major factor limiting crop growth and development in many areas. Switchgrass (Panicum virgatum L.) is an important warm-season grass species used for biofuel production. The objective of this study was to investigate antioxidant metabolism, proline,and protein variation associated with alkali-salt tolerance among 30 switchgrass lines and identify metabolic markers for evaluating alkali-salt tolerance of switchgrass lines. The grass lines were transplanted into plastic pots containing fine sand. When the plants reached E5 developmental stage, they were subjected to either alkali-salt stress treatment (150 mM Na+ and pH of 9.5) or control (no alkali-salt stress) for 20 d. The 30 switchgrass lines differed in alkali-salt tolerance as determined by the level of leaf malondialdehyde (MDA), antioxidant enzyme activity [(superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX)], proline and protein. Alkali-salt stress increased MDA, proline, SOD, reduced CAT activity, but its effect on protein and APX varied depending on lines. Wide variations in the five parameters existed among the 30 lines. In general, the lines with higher CAT activity and lower proline content under alkali-salt stress had less MDA, exhibiting better alkali-salt tolerance. Among the five parameters, CAT can be considered as valuable metabolic markers for assessment of switchgrass tolerance to alkali-salt stress.

Isolation, expression, and functional analysis of developmentally regulated plasma membrane polypeptide 1 (DREPP1) in Sporobolus virginicus grown under alkali salt stress.

The plant specific DREPP proteins have been shown to bind Ca2+ and regulate the N-myristoylation signaling and microtubule polymerization in Arabidopsis thaliana. The information about DREPP proteins in other plants is, however, scarce. In the present study, we isolated the DREPP gene from a halophytic grass, Sporobolus virginicus, and tested whether the gene was involved in alkaline salt stress responses. The SvDREPP1 was cloned from S. virginicus by RACE methods. The isolated gene showed high homology to DREPP homologs from C4 grasses, Setaria italica, and Panicum hallii as well as rice (OsDREPP1). The encoded protein contained 202 amino acid residues. It was expressed in E. coli, and its biochemical properties were studied. It was observed that SvDREPP1 was not only Ca2+-binding protein, but also bind to calmodulin and microtubules. The SvDREPP1 mRNA expression in plants grown under alkaline salt stress was upregulated by 3.5 times over the control in leaf tissues after 48-h treatment, whereas it was increased for 6.0 times in the root tissues at 36h. The data suggests the importance of SvDREPP1 in regulating alkali salt stress responses in the leaf tissues.

Metabolomics and its physiological regulation process reveal the salt-tolerant mechanism in Glycine soja seedling roots

Wild soybean (Glycine soja) is an excellent germplasm resource and has strong resistance and wide adaptability to different environments. Hence, the physiology and metabolomics characteristics of wild soybean under different types of salt stress were determined to improve understanding of salt-tolerant mechanisms of wild soybean in the field. Two types of wild soybean seedlings were exposed to two different types of salt stress for 14 d. The photosynthesis of wild soybean seedling extracts were analyzed using metabolomics based on gas chromatography-mass spectrometry. The wild soybean root extracts used metabolomics to quantify the metabolic changes and ion contents. The assimilative function of photosynthesis in salt-tolerant wild soybean was less inhibited than in common wild soybean, and it regulated accumulation of toxic ions and maintained the accumulation of K+ and Mg2+ to alleviate salt stress. Moreover, in resisting salt stress the salt-tolerant wild soybean has showed improved amino acid and carbohydrate and polyol metabolisms under neutral-salt stress and organic acid, amino acid and tricarboxylic acid metabolisms under alkali-salt stress. Our results provide valuable insights into the response of salt-tolerant wild soybean to two types of salt stress by linking stress-related physiological responses to changes in metabolites.

Metabolomics Analysis Reveals the Salt-Tolerant Mechanism in Glycine soja

Salinity is one of the major environmental constraints limiting crop plant yields around the world. Therefore, understanding the salt-tolerant mechanism and improving crop salt tolerance are two of the most effective ways of sustaining crop production worldwide. The differences in metabolite profiles were analyzed between common wild soybean and salt-tolerant wild soybean in response to neutral-salt stress and alkali-salt stress to elucidate the salt-tolerant mechanism. The results showed salt-tolerant wild soybean grew better than common wild soybean under both treatments. Differential metabolites profiling showed that the levels of some carbohydrates and fatty acids were lower in common wild soybean than in salt-tolerant wild soybean under salt stress. These metabolites included lactose, ribose, lauric acid, palmitic acid, stearic acid, and linolenic acid. Amino acid accumulation was observed in the two wild soybeans under alkali-salt stress. These amino acids were valine, tyrosine, glutamic acid, leucine, and isoleucine. The content of most organic acids and proline increased in salt-tolerant wild soybean subjected to alkali-salt stress. These organic acids included mucic acid, glutaric acid, galactonic acid, and dehydroascorbic acid. The TCA cycle was enhanced in common wild soybean in response to both treatments, but was reduced in salt-tolerant wild soybean. This study demonstrated the salt-tolerant mechanism in common wild soybean may encourage the TCA cycle to generate more ATP. However salt-tolerant wild soybean may regulate amino acid and organic acid metabolism to generate more compatible solutes. These findings provide an important theoretical foundation for the protection, development, and utilization of wild soybean resources.

Comparison of Ionomic and Metabolites Response under Alkali Stress in Old and Young Leaves of Cotton (Gossypium hirsutum L.) Seedlings.

Soil salinization is an important agriculture-related environmental problem. Alkali stress and salt stress strongly influence the metabolic balance in plants. Salt and alkali stresses exert varied effects on old and young tissues, which display different adaptive strategies. In this study, we used cotton (Gossypium hirsutum L.) plants as experimental material to investigate whether alkali stress induces ionic and metabolism changes in old and young leaves of cotton plants exposed to alkali stress. Results showed that alkali stress exerted a considerably stronger growth inhibition on old leaves than on young leaves. Under alkali stress, young leaves can maintain low Na and high K contents and retain relatively stable tricarboxylic acid cycle, resulting in greater accumulation of photosynthetic metabolites. In terms of metabolic response, the young and old leaves clearly displayed different mechanisms of osmotic regulation. The amounts of inositol and mannose significantly increased in both old and young leaves of cotton exposed to alkali stress, and the extent of increase was higher in young leaves than in old leaves. In old leaves, synthesis of amino acids, such as GABA, valine, and serine, was dramatically enhanced, and this phenomenon is favorable for osmotic adjustment and membrane stability. Organs at different developmental stages possibly display different mechanisms of metabolic regulation under stress condition. Thus, we propose that future investigations on alkali stress should use more organs obtained at different developmental stages.

Metabolic Profiles Reveal Changes in Wild and Cultivated Soybean Seedling Leaves under Salt Stress.

Clarification of the metabolic mechanisms underlying salt stress responses in plants will allow further optimization of crop breeding and cultivation to obtain high yields in saline-alkali land. Here, we characterized 68 differential metabolites of cultivated soybean (Glycine max) and wild soybean (Glycine soja) under neutral-salt and alkali-salt stresses using gas chromatography-mass spectrometry (GC-MS)-based metabolomics, to reveal the physiological and molecular differences in salt tolerance. According to comparisons of growth parameters under the two kinds of salt stresses, the level of inhibition in wild soybean was lower than in cultivated soybean, especially under alkali-salt stress. Moreover, wild soybean contained significantly higher amounts of phenylalanine, asparagine, citraconic acid, citramalic acid, citric acid and α-ketoglutaric acid under neutral-salt stress, and higher amounts of palmitic acid, lignoceric acid, glucose, citric acid and α-ketoglutaric acid under alkali-salt stress, than cultivated soybean. Further investigations demonstrated that the ability of wild soybean to salt tolerance was mainly based on the synthesis of organic and amino acids, and the more active tricarboxylic acid cycle under neutral-salt stress. In addition, the metabolite profiling analysis suggested that the energy generation from β-oxidation, glycolysis and the citric acid cycle plays important roles under alkali-salt stress. Our results extend the understanding of mechanisms involved in wild soybean salt tolerance and provide an important reference for increasing yields and developing salt-tolerant soybean cultivars.

Physiological Evaluation of Alkali-Salt Tolerance of Thirty Switchgrass (Panicum virgatum) Lines.

Soil salt-alkalization is a major limiting factor for crop production in many regions. Switchgrass (Panicum virgatum L.) is a warm-season C4 perennial rhizomatous bunchgrass and a target lignocellulosic biofuel species. The objective of this study was to evaluate relative alkali-salt tolerance among 30 switchgrass lines. Tillers of each switchgrass line were transplanted into pots filled with fine sand. Two months after transplanting, plants at E5 developmental stage were grown in either half strength Hoagland’s nutrient solution with 0 mM Na+ (control) or half strength Hoagland’s nutrient solution with 150 mM Na+ and pH of 9.5 (alkali-salt stress treatment) for 20 d. Alkali-salt stress damaged cell membranes [higher electrolyte leakage (EL) ], reduced leaf relative water content (RWC), net photosynthetic rate (Pn), stomatal conductance (gs), and transpiration rate (Tr). An alkali-salt stress tolerance trait index (ASTTI) for each parameter was calculated based on the ratio of the value under alkali-salt stress and the value under non-stress conditions for each parameter of each line. Relative alkali-salt tolerance was determined based on principal components analysis and cluster analysis of the physiological parameters and their ASTTI values. Significant differences in alkali-salt stress tolerance were found among the 30 lines. Lowland lines TEM-SEC, Alamo, TEM-SLC and Kanlow were classified as alkali-salt tolerant. In contrast, three lowland lines (AM-314/MS-155, BN-13645-64) and two upland lines (Caddo and Blackwell-1) were classified as alkali-salt sensitive. The results suggest wide variations exist in alkali-salt stress tolerance among the 30 switchgrass lines. The approach of using a combination of principal components and cluster analysis of the physiological parameters and related ASTTI is feasible for evaluating alkali-salt tolerance in switchgrass.

Cloning of Coding Sequence of Glutamin Synthetase from Polygonum sibiricum Laxm. and Its Expression under Alkali Salinity Stress

The full-length of Glutamin synthetase( termed PsGS) gene was cloned using RACE( rapid amplification of cDNA end) technology based on GS partial sequence obtained from a random clone in SSH library of Polygonum sibiricum Laxm.. The acquired 1 273 bp sequence includes a 5' untranslated region of 178 bp,a 3' untranslated region of 24 bp with poly( A),and an open reading frame( ORF) encoding 356 amino acids. Based on the comparison with amino acid sequences of other plant glutamin synthetase and the phylogenetic analysis of protein evolution,this gene was divided into glutamin synthetase family. The expression analyses by RT-PCR showed that PsGS expressed in leaves,stems and rhizomes of P. sibiricum Laxm.. Under the induction of 3% NaHCO3,the expression of PsGS was significantly influenced,which suggested that PsGS might play an important role in alkali salt stress resistance.