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PubMed2001

Comparative salt tolerance of amphidiploid and diploid Brassica species.

Salt (NaCl) tolerance of three amphidiploid Brassica species, B. napus (AC genome), B. carinata (BC genome), and B. juncea (AB genome), and their putative diploid relatives, B. campestris (A genome), B. oleracea (C genome) and B. nigra (B genome) was examined under glasshouse conditions. The plants were grown in sand culture throughout the study period (51 days). Twenty-three day old plants of all six species were subjected for 28 days to control (0 mol m(-3) NaCl), 100 and 200 mol m(-3) NaCl in Hoagland nutrient solution. Under saline conditions, growth of the three amphidiploid species was significantly greater in shoot and root weights, and seed yield was greater than that of the diploids. The amphidiploids accumulated lower Na(+) but higher K(+) in their shoots and roots, the K/Na ratio therefore being considerably higher than those of the diploids. Ca(2+) accumulation was similar in the diploids and amphidiploids, and the Cl(-) accumulation pattern was not consistent in the different species. The occurrence of high salt tolerance of amphidiploids, and their enhanced K/Na discrimination with respect to their diploid relatives, suggests that salt tolerance has been obtained from A and C genomes and the latter trait from all three genomes (A, B, and C).

Journal Article↗
PubMed2005

Developing salt-tolerant crop plants: challenges and opportunities.

Soil salinity, one of the major abiotic stresses reducing agricultural productivity, affects large terrestrial areas of the world; the need to produce salt-tolerant crops is evident. Two main approaches are being used to improve salt tolerance: (i) the exploitation of natural genetic variations, either through direct selection in stressful environments or through mapping quantitative trait loci and subsequent marker-assisted selection; and (ii) the generation of transgenic plants to introduce novel genes or to alter expression levels of the existing genes to affect the degree of salt stress tolerance. Here, we discuss the challenges and opportunities provided by recently developed functional tools for the development of salt-tolerant crops.

Adaptation, Physiological↗
PubMed2000

Molecular cloning and chromosomal localization of human salt-tolerant protein.

We have isolated a novel human cDNA coding for human salt-tolerant protein (HSTP), that is a homologue of the rat salt-tolerant protein (STP) and may contribute to salt-induced hypertension by modulating renal cation transport. The nucleotide sequence (1988bp) of the HSTP cDNA contains an open reading frame encoding a polypeptide comprising 545 amino acids, two residues fewer than the rat STP cDNA. The predicted amino acid sequence exhibits 92% identity to that of the rat protein. HSTP contains predicted coiled-coil domains and Src Homology 3 domain, and shows a high degree of identity to CIP4 (Cdc42 target protein) and human Trip 10 (thyroid-hormone receptor interacting protein). We have mapped the HSTP gene to human chromosome 19 by fluorescence in situ hybridization.

Amino Acid Sequence↗
PubMed1984

Cell wall and phospholipid composition and their contribution to the salt tolerance of Halomonas elongata.

The salt-tolerant bacterium Halomonas elongata makes a variety of physiological adaptations in response to increases in the salt concentration of its growth medium. The cell walls become more compact and internally coherent. The overall lipid pattern shows an increased amount of negatively charged lipids. In addition, the peptidoglycan composition of H. elongata, although not changing in response to increased NaCl, contains the hydrophobic amino acid leucine which is unique among bacterial species. The results suggest that H. elongata is able to live in a wide variety of salt concentrations because it alters its cell physiology in ways which increase both structural integrity and the amount of less-mobile, "structured" cell water, making the cells less susceptible to NaCl-induced dehydration.

Acclimatization↗
PubMed1996

SOS1, a Genetic Locus Essential for Salt Tolerance and Potassium Acquisition.

To begin to determine which genes are essential for salt tolerance in higher plants, we identified four salt-hypersensitive mutants of Arabidopsis by using a root-bending assay on NaCl-containing agar plates. These mutants (sos1-1, sos1-2, sos1-3, and sos1-4) are allelic to each other and were caused by single recessive nuclear mutations. The SOS1 gene was mapped to chromosome 2 at 29.5 [plusmn] 6.1 centimorgans. The mutants showed no phenotypic changes except that their growth was >20 times more sensitive to inhibition by NaCl. Salt hypersensitivity is a basic cellular trait exhibited by the mutants at all developmental stages. The sos1 mutants are specifically hypersensitive to Na+ and Li+. The mutants were unable to grow on media containing low levels (below ~1 mM) of potassium. Uptake experiments using 86Rb showed that sos1 mutants are defective in high-affinity potassium uptake. sos1 plants became deficient in potassium when treated with NaCl. The results demonstrate that potassium acquisition is a critical process for salt tolerance in glycophytic plants.

Journal Article↗
PubMed2006

Nitric oxide enhances salt tolerance in maize seedlings through increasing activities of proton-pump and Na+/H+ antiport in the tonoplast.

Nitric oxide (NO), an endogenous signaling molecule in animals and plants, mediates responses to abiotic and biotic stresses. Our previous work demonstrated that 100 microM sodium nitroprusside (SNP, an NO donor) treatment of maize seedlings increased K(+) accumulation in roots, leaves and sheathes, while decreasing Na(+) accumulation (Zhang et al. in J Plant Physiol Mol Biol 30:455-459, 2004b). Here we investigate how NO regulates Na(+), K(+) ion homeostasis in maize. Pre-treatment with 100 muM SNP for 2 days improved later growth of maize plants under 100 mM NaCl stress, as indicated by increased dry matter accumulation, increased chlorophyll content, and decreased membrane leakage from leaf cells. An NO scavenger, methylene blue (MB-1), blocked the effect of SNP. These results indicated that SNP-derived NO enhanced maize tolerance to salt stress. Further analysis showed that NaCl induced a transient increase in the NO level in maize leaves. Both NO and NaCl treatment stimulated vacuolar H(+)-ATPase and H(+)-PPase activities, resulting in increased H(+)-translocation and Na(+)/H(+) exchange. NaCl-induced H(+)-ATPase and H(+)-PPase activities were diminished by MB-1. 1-Butanol, an inhibitor of phosphatidic acid (PA) production by phospholipase D (PLD), reduced NaCl- and NO-induced H(+)-ATPase activation. In contrast, applied PA stimulated H(+)-ATPase activity. These results suggest that NO acts as a signal molecule in the NaCl response by increasing the activities of vacuolar H(+)-ATPase and H(+)-PPase, which provide the driving force for Na(+)/H(+) exchange. PLD and PA play an important role in this process.

Cell Membrane↗
PubMed2004

Overexpression of the AP2/EREBP transcription factor OPBP1 enhances disease resistance and salt tolerance in tobacco.

Osmotin promoter binding protein 1 (OPBP1), an AP2/EREBP-like transcription factor of tobacco (Nicotiana tabacum), was isolated using a yeast one-hybrid system. RNA gel blot analysis indicated that expression of the OPBP1 gene was induced by elicitor cryptogein, NaCl, ethephon, methyl jasmonate, as well as cycloheximide. Transient expression analysis using an OPBP1-eGFP fusion gene in onion epidermal cells revealed that the OPBP1 protein was targeted to the nuclear. Further, electrophoretic mobility shift assays demonstrated that the recombinant OPBP1 protein could bind to an oligonucleotide containing the GCC-box cis element. Transgenic tobacco plants with an over expression of the OPBP1 gene accumulated high levels of PR-1a and PR-5d genes and exhibited enhanced resistance to infection by Pseudomonas syringae pv tabaci and Phytophthora parasitica var nicotianae pathogens. They also exhibited increased tolerance to salt stress. These results suggest that OPBP1 might be a transcriptional regulator capable of regulating expression in sets of stress-related genes.

Acetates↗
PubMed2003

Functional analysis of AtHKT1 in Arabidopsis shows that Na(+) recirculation by the phloem is crucial for salt tolerance.

Two allelic recessive mutations of Arabidopsis, sas2-1 and sas2-2, were identified as inducing sodium overaccumulation in shoots. The sas2 locus was found (by positional cloning) to correspond to the AtHKT1 gene. Expression in Xenopus oocytes revealed that the sas2-1 mutation did not affect the ionic selectivity of the transporter but strongly reduced the macro scopic (whole oocyte current) transport activity. In Arabidopsis, expression of AtHKT1 was shown to be restricted to the phloem tissues in all organs. The sas2-1 mutation strongly decreased Na(+) concentration in the phloem sap. It led to Na(+) overaccumulation in every aerial organ (except the stem), but to Na(+) underaccumulation in roots. The sas2 plants displayed increased sensitivity to NaCl, with reduced growth and even death under moderate salinity. The whole set of data indicates that AtHKT1 is involved in Na(+) recirculation from shoots to roots, probably by mediating Na(+) loading into the phloem sap in shoots and unloading in roots, this recirculation removing large amounts of Na(+) from the shoot and playing a crucial role in plant tolerance to salt.

Adaptation, Physiological↗
PubMed2005

Enhanced salt tolerance mediated by AtHKT1 transporter-induced Na unloading from xylem vessels to xylem parenchyma cells.

AtHKT1 is a sodium (Na+) transporter that functions in mediating tolerance to salt stress. To investigate the membrane targeting of AtHKT1 and its expression at the translational level, antibodies were generated against peptides corresponding to the first pore of AtHKT1. Immunoelectron microscopy studies using anti-AtHKT1 antibodies demonstrate that AtHKT1 is targeted to the plasma membrane in xylem parenchyma cells in leaves. AtHKT1 expression in xylem parenchyma cells was also confirmed by AtHKT1 promoter-GUS reporter gene analyses. Interestingly, AtHKT1 disruption alleles caused large increases in the Na+ content of the xylem sap and conversely reduced the Na+ content of the phloem sap. The athkt1 mutant alleles had a smaller and inverse influence on the potassium (K+) content compared with the Na+ content of the xylem, suggesting that K+ transport may be indirectly affected. The expression of AtHKT1 was modulated not only by the concentrations of Na+ and K+ but also by the osmolality of non-ionic compounds. These findings show that AtHKT1 selectively unloads sodium directly from xylem vessels to xylem parenchyma cells. AtHKT1 mediates osmolality balance between xylem vessels and xylem parenchyma cells under saline conditions. Thus AtHKT1 reduces the sodium content in xylem vessels and leaves, thereby playing a central role in protecting plant leaves from salinity stress.

Arabidopsis↗
PubMed2001

Immobilized salt-tolerant yeasts: application of a new polyethylene-oxide support in a continuous stirred-tank reactor for flavour production.

Immobilization of salt-tolerant yeasts considerably decreases the total time required for the flavour development in soy-sauce processes. For immobilization of cells, alginate gel is mostly used as support material. However, alginate is not very suitable for use in soy-sauce processes because alginate is sensitive to abrasion and chemically unstable towards the high salt content of the soy-sauce medium. In contrast, a newly developed polyethylene-oxide gel seems to be more suitable, but this gel has not been used so far for flavour production in a bioreactor with a high salt content. Therefore, this gel was applied with immobilized salt-tolerant yeasts in a continuous stirred-tank reactor, containing more than 12.5% (w/v) salt. In this reactor, the polyethylene-oxide gel particles did not show any abrasion for several days, while alginate gel beads were already destroyed within 1 day. In addition, the polyethylene-oxide gel particles with immobilized salt-tolerant yeasts Candida versatilis and Zygosaccharomyces rouxii showed a good flavour production. From this work, it was concluded that the application of polyethylene-oxide gel in long-term soy-sauce processes is attractive in the case the sticking together of polyethylene-oxide gel particles can be controlled.

Alginates↗
PubMed1989

Polyamines as modulators of salt tolerance in rice cultivars.

The effect of NaCl on the endogenous levels of diamine, putrescine and polyamines, spermidine and spermine, was studied in the shoot system of salt-tolerant and salt-sensitive lines of rice (Oryza sativa L.) cultivars during three growth stages. Salt stress increased the levels of diamine and polyamine in varying degrees among nine rice cultivars investigated. Salt tolerant AU1, Co43, and CSC1 were effective in maintaining high concentrations of spermidine and spermine, while the content of putrescine was not significantly altered in all the growth stages when plants were exposed to salinity. The salt sensitivity in rice was associated with excessive accumulation of putrescine and with low levels of spermidine and spermine in the shoot system of salt-sensitive cultivars Co36, CSC2, GR3, IR20, TKM4, and TKM9 under saline condition. One of the possible mechanisms of saline resistance was observed to be due to the highly increased polyamines against the low increase in diamines. Alternatively, the salt sensitivity could be due to high increase of diamines and an incapacity to maintain high levels of polyamines.

Journal Article↗
PubMed1976

Genotypic Responses to Salinity: Differences between Salt-sensitive and Salt-tolerant Genotypes of the Tomato.

Four ecotypes of the species Lycopersicon cheesmanii ssp. minor (Hook.) C.H. Mull. from the Galapagos Islands were compared with L. esculentum Mill cv. VF 36 with respect to salt tolerance. The L. cheesmanii ecotype that proved most salt-tolerant was selected for detailed comparison with the L. esculentum cultivar. Plants were grown in modified Hoagland solution salinized with synthetic seawater salt mix. Growth rates under saline conditions were examined and amino acid, sugar, total amino nitrogen, free acidity, and Na and K levels in the tissues of the most and least tolerant plants were measured under salt stress and nonstress conditions. Results indicate that all Galapagos ecotypes were far more salt-tolerant than was the esculentum cultivar. They could survive in full strength seawater nutrient solution while the esculentum cultivar could not in most cases withstand levels higher than 50% seawater. Growth rates were reduced in both species under saline conditions but the esculentum cultivar was more severely affected. High levels of total amino nitrogen, specific amino acids, and free acidity along with low sodium content were found in the salt stressed VF 36 cultivar. The opposite responses were noted in the salt stressed treatments of the Galapagos ecotype. Tissue sugar levels did not appear to be similarly correlated with salt stress in either species. Potassium content fell sharply during salinization in the Galapagos ecotype while in the esculentum cultivar it declined relatively little even at high levels of salinity.

Journal Article↗
PubMed2001

Mutation in PMR1, a Ca(2+)-ATPase in Golgi, confers salt tolerance in Saccharomyces cerevisiae by inducing expression of PMR2, an Na(+)-ATPase in plasma membrane.

Sodium tolerance in yeast is enhanced by continuous activation of calcineurin, a Ca(2+)/calmodulin-dependent protein phosphatase that is required for modulation of the Na(+) efflux mechanism. We isolated several salt-tolerant mutations with the treatment of ethylmethane sulfonate under high salt stress. One of the mutations was mapped in the PMR1 gene. Pmr1p, the P-type Ca(2+)-ATPase in the Golgi apparatus, regulates a cytosolic Ca(2+) level in various responses. Cytosolic Ca(2+) concentration in the pmr1 mutant is highly maintained, and thus calcineurin is activated continuously. The treatment of FK506, a specific inhibitor of calcineurin, abolishes the salt-tolerant phenotype of the pmr1 mutant. Activated calcineurin induces the expression of PMR2, encoding the P-type Na(+)-ATPase, through the specific transcription factor, Tcn1p/Crz1p. Also, expression of the PMR2::lacZ reporter gene in the pmr1 mutant was higher than that in wild type. We propose that the pmr1 mutation confers salt tolerance through continuous activation of calcineurin and that Pmr1p might act as a major Ca(2+)-ATPase under high salt stress.

Adenosine Triphosphatases↗
PubMed2001

[Detection of the wheat salt-tolerant-mutant using PCR-SSCP combining with direct sequenceing].

gf-2.8 is a gene located on the chromosomal homologous group 4, which was reported to have relationship with salt tolerance of wheat. A pair of primers were designed to amplify the coding region of gf-2.8 in the two salt-tolerant mutants and their parents. Agarose gel electrophoresis showed that the 685 bp band was amplified among all the materials. SSCP analysis suggested that 974915 (one of the mutants) was different from the other materials. The sequencing results showed that Jimai 24 and its salt-tolerant mutant 8901-17 had the same sequence as published, which indicated that the mutation site of 8901-17 was not on the gf-2.8 gene. However, there were at least two single base mutations in the gf-2.8 of 974915, one of which caused the alternation of amino acid, this mutation occurred in the conservative region of gf-2.8.

Base Sequence↗
PubMed1987

Relationship between Sodium Influx and Salt Tolerance of Nitrogen-Fixing Cyanobacteria.

The relationship between sodium uptake and cyanobacterial salt (NaCl) tolerance has been examined in two filamentous, heterocystous, nitrogen-fixing species of Anabaena. During diazotrophic growth at neutral pH of the growth medium, Anabaena sp. strain L-31, a freshwater strain, showed threefold higher uptake of Na than Anabaena torulosa, a brackish-water strain, and was considerably less salt tolerant (50% lethal dose of NaCl, 55 mM) than the latter (50% lethal dose of NaCl, 170 mM). Alkaline pH or excess K (>25 mM) in the medium causes membrane depolarization and inhibits Na influx in both cyanobacteria (S. K. Apte and J. Thomas, Eur. J. Biochem. 154:395-401, 1986). The presence of nitrate or ammonium in the medium caused inhibition of Na influx accompanied by membrane depolarization. These experimental manipulations affecting Na uptake demonstrated a good negative correlation between Na influx and salt tolerance. All treatments which inhibited Na influx (such as alkaline pH, K above 25 mM, NO(3), and NH(4)), enhanced salt tolerance of not only the brackish-water but also the freshwater cyanobacterium. The results indicate that curtailment of Na influx, whether inherent or effected by certain environmental factors (e.g., combined nitrogen, alkaline pH), is a major mechanism of salt tolerance in cyanobacteria.

Journal Article↗
PubMed2000

[Subcloning and sequencing of DNA fragment related to salt tolerance in Sinorhizobium fredii RT19].

A 23 kb DNA fragment related to salt tolerance was obtained from the gene library of S. fredii strain RT19. In this study, BamH I was selected to digest 23 kb DNA fragment into different length of DNA fragments. The resulting fragments were ligated with plasmid pML122, then the recombinant plasmids were transformed to competent cells of E. coli S17-1 on selective medium and three transformants TR were obtained. Two-parental mating experiments were carried out with these transformants as donor and salt sensitive S. fredii strain RC3-3 as recipient, and the transconjugant BR2 was selected on FY plates containing gentamycin and 0.4 mol/L NaCl. Thus, a 4.4 kb DNA fragment related to salt tolerance was obtained. Based on its physical map, six restriction fragments were subcloned into plasmid pUC18 for DNA sequencing. Subsequently, sequencing and analysis of 4.4 kb DNA fragment showed that fixO, fixN genes and three ORFs were obtained.

Amino Acid Sequence↗
PubMed2001

Transfer of salt tolerance from Aeleuropus littorulis sinensis to wheat (Triticum aestivum L.) via asymmetric somatic hybridization.

Protoplasts of wheat c.v. Jinan 177 were fused by PEG method with the UV irradiated protoplasts of A. littoralis - a salt tolerant plant intertribal to wheat. The early-formed regenerated clones were identified as hybrids by chromosome, isozyme and RAPD analysis. Their salt-tolerant ability was compared with both parents in relative growth, proline accumulation and Na(+)/K(+) ratio under salt stress, and was proved higher than wheat, indicating some corresponding genes coding salt-tolerance had been transferred into the hybrids. However, the hybrid clones could only differentiated to albino plants. Further investigations are now being conducted to solve this problem.

Journal Article↗