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PubMed2001

Response of the cultivated tomato and its wild salt-tolerant relative Lycopersicon pennellii to salt-dependent oxidative stress: The root antioxidative system.

The response of the antioxidant system to salt stress was studied in the roots of the cultivated tomato Lycopersicon esculentum Mill. cv. M82 (Lem) and its wild salt-tolerant relative L. pennellii (Corr.) D'Arcy accession Atico (Lpa). Roots of control and salt (100 mM NaCl)-stressed plants were sampled at various times after commencement of salinization. A gradual increase in the membrane lipid peroxidation in salt-stressed root of Lem was accompanied with decreased activities of the antioxidant enzymes: superoxide dismutase (SOD; EC 1.15.1.1), catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APX; EC 1.11.1.11) and decreased contents of the antioxidants ascorbate and glutathione and their redox states. In contrast, increased activities of the SOD, CAT, APX, monodehydroascorbate reductase (MDHAR; EC 1.6.5.4), and increased contents of the reduced forms of ascorbate and glutathione and their redox states were found in salt-stressed roots of Lpa, in which the level of membrane lipid peroxidation remained unchanged. It seems that the better protection of Lpa roots from salt-induced oxidative damage results, at least partially, from the increased activity of their antioxidative system.

Journal Article↗

PubMed1996

Two related rolling circle replication plasmids from salt-tolerant bacteria.

In a range of salt-tolerant bacteria isolated from soil, rhizosphere, and phyloplane, cross-hybridization tests revealed a group of seven plasmids which were chosen for further study. Two plasmids (pSH1418 and pSH1451) were picked as representative examples of the two related subgroups. Restriction mapping and Southern blotting identified a region common to the two plasmids which later was identified as encoding the replication functions. We were unable to join these plasmids to high-copy-number vectors but this was possible with low-copy-number IncP vectors. In Escherichia coli, cloned plasmids pSH1418 and pSH1451 conferred salt tolerance but the phenotype was unstable, with the loss of salt tolerance apparently being correlated with structural instability of the plasmid DNA. Plasmid pSH1451 was sequenced and shown to be closely related to RCR plasmids of Gram-positive bacteria. The host of this plasmid was classified as Bacillus pumilus by rDNA typing and lipid profiling by gas chromatography. A number of open reading frames (orfs) which could code for salt tolerance or other functions were identified in the plasmid sequence. Sequence similarity to previously sequenced genes suggested that the products of orf4 and orf5 may work together to transport a molecule such as aspartate ion that may promote osmotolerance.

Amino Acid Sequence↗

PubMed2004

Transgenic evaluation of activated mutant alleles of SOS2 reveals a critical requirement for its kinase activity and C-terminal regulatory domain for salt tolerance in Arabidopsis thaliana.

In Arabidopsis thaliana, the calcium binding protein Salt Overly Sensitive3 (SOS3) interacts with and activates the protein kinase SOS2, which in turn activates the plasma membrane Na(+)/H(+) antiporter SOS1 to bring about sodium ion homeostasis and salt tolerance. Constitutively active alleles of SOS2 can be constructed in vitro by changing Thr(168) to Asp in the activation loop of the kinase catalytic domain and/or by removing the autoinhibitory FISL motif from the C-terminal regulatory domain. We expressed various activated forms of SOS2 in Saccharomyces cerevisiae (yeast) and in A. thaliana and evaluated the salt tolerance of the transgenic organisms. Experiments in which the activated SOS2 alleles were coexpressed with SOS1 in S. cerevisiae showed that the kinase activity of SOS2 is partially sufficient for SOS1 activation in vivo, and higher kinase activity leads to greater SOS1 activation. Coexpression of SOS3 with SOS2 forms that retained the FISL motif resulted in more dramatic increases in salt tolerance. In planta assays showed that the Thr(168)-to-Asp-activated mutant SOS2 partially rescued the salt hypersensitivity in sos2 and sos3 mutant plants. By contrast, SOS2 lacking only the FISL domain suppressed the sos2 but not the sos3 mutation, whereas truncated forms in which the C terminus had been removed could not restore the growth of either sos2 or sos3 plants. Expression of some of the activated SOS2 proteins in wild-type A. thaliana conferred increased salt tolerance. These studies demonstrate that the protein kinase activity of SOS2 is partially sufficient for activation of SOS1 and for salt tolerance in vivo and in planta and that the kinase activity of SOS2 is limiting for plant salt tolerance. The results also reveal an essential in planta role for the SOS2 C-terminal regulatory domain in salt tolerance.

Adaptation, Physiological↗

PubMed2003

Induction of salt tolerance in Bacillus subtilis IFO 3025.

Salt tolerance was induced in Bacillus subtilis IFO 3025 cells when a moderate osmotic stress was imposed by incubation in the presence of compatible solutes and 0.5 M NaCl or 0.8 M sorbitol. The optimum condition for inducing salt tolerance was observed when the cells were incubated in a solution containing 5 mM glutamate, 2.5 mM KCl, and 0.5 M NaCl or 0.8 M sorbitol. After 60 min incubation, the cells were able to form colonies on an agar plate with high salinity. It was confirmed that the cells acquired salt tolerance by accumulating glutamate and potassium ions in the cytoplasm as the main solute and ion, respectively.

Journal Article↗

PubMed2006

Salinity tolerance of 'Valencia' orange trees on rootstocks with contrasting salt tolerance is not improved by moderate shade.

The effects of shading in combination with salinity treatments were studied in citrus trees on two rootstocks with contrasting salt tolerance to determine if shading could reduce the negative effects of salinity stress. Well-nourished 2-year-old 'Valencia' orange trees grafted on Cleopatra mandarin (Cleo, relatively salt tolerant) or Carrizo citrange (Carr, relatively salt sensitive), were grown either under a 50% shade cloth or left unshaded in full sunlight. Half the trees received no salinity treatment and half were salinized with 50 mM Cl- during two 9 week salinity periods in the spring and autumn interrupted by an 11 week rainy period. The shade treatment reduced midday leaf temperature and leaf-to-air vapour pressure deficit regardless of salinity treatments. In non-salinized trees, shade increased midday CO2 assimilation rate (A(CO2)) and stomatal conductance, but had no effect on leaf transpiration (E(lf)). Shade also increased leaf chlorophyll and photosynthetic water use efficiency (A(CO2)/E(lf)) in leaves on both rootstocks and increased total plant dry weight in Cleo. The salinity treatment reduced leaf growth and leaf gas exchange parameters. Shade decreased Cl- concentrations in leaves of salinized Carr trees, but had no effect on leaf or root Cl- of trees on Cleo. There were no significant differences in leaf gas exchange parameters of shaded and unshaded salinized plants but the growth reduction from salinity stress was actually greater for shaded than for unshaded trees. Shaded trees on both rootstocks had higher leaf Na+ than unshaded trees after the first salinity period, and this shade-induced elevated leaf Na+ persisted after the second salinity period in trees on Carr. Thus, shading did not alleviate the negative effects of salinity on growth and Na+ accumulation.

Carbon Dioxide↗

PubMed2002

Expression of mangrove allene oxide cyclase enhances salt tolerance in Escherichia coli, yeast, and tobacco cells.

To analyze the mechanisms of salt tolerance in the mangrove plant, Bruguiera sexangula, functional screening for cDNAs encoding proteins essential for salt tolerance was performed using Escherichia coli as the host organism. A transformant expressing a protein homologous to Lycopersicon (tomato) allene oxide cyclase (AOC) displayed enhanced salt tolerance. However, this unusual trait is not conferred by Lycopersicon AOC or its Arabidopsis homolog. Analysis of the functional region revealed a sequence of only 70 amino acids, which contains an unusual sequence that is essential for the salt-tolerant phenotype. On the basis of its unusual function, the mangrove AOC homolog is designated "mangrin". Furthermore, expression of mangrin driven by the GAL1 promoter and the 35S cauliflower mosaic virus (CaMV) promoter in Saccharomyces cerevisiae and tobacco cell lines, respectively, also gave rise to enhanced salt tolerance. Mangrin transcripts increased in cultured B. sexangula cells in response to salt stress. We propose that mangrin plays an important role in the salt-tolerance mechanism of B. sexangula, and that the biosynthesis of mangrin might be an effective means of enhancing salt tolerance in higher plants.

Adaptation, Physiological↗

PubMed2026

Identification and analysis of HD-ZIP transcription factors that regulate salt gland development and salt tolerance in Limonium bicolor.

Soil salinity severely constrains agricultural production. Elucidating the salt-tolerance mechanisms of halophytes can provide innovative approaches for improving the salt tolerance of crop plants. In this study, we performed genome-wide identification and analysis of 36 LbHDZ genes encoding homeodomain-leucine zipper (HD-ZIP) transcription factors in Limonium bicolor, a typical recretohalophyte that excretes excess salt ions through specialized salt glands. Expression profiling across different stages of salt gland development, as well as in various tissues under salt stress, indicated that multiple LbHDZ genes are involved in regulating salt gland development and salt tolerance. Among these genes, LbHDZ14 (a member of the HD-ZIP II subfamily) exhibited sustained high expression during the critical period of salt gland formation, while its transcript levels were significantly downregulated in leaves and roots under salt stress. Subsequent experiments demonstrated that LbHDZ14 is localized in the nucleus and negatively regulates salt gland density and salt tolerance by directly binding to the promoter of LbGDSL, a positive regulator of salt gland development. In conclusion, this study reveals the expression patterns of LbHDZ genes in L. bicolor, characterizes the functional mechanism of LbHDZ14, further elucidates the regulatory network underlying salt gland development, and provides candidate genes for enhancing crop salt tolerance.

Plumbaginaceae↗

PubMed2000

[Studies of salt tolerance of alloplasmic wheat].

Using Aegilops crassa cytoplasm wheat as test material, salt tolerance of alloplasmic wheat was identified by tissue culture, nutrient solution culture and artificial saline pond, from calli, seeding stage, recovering stage and mature period. The results showed Ae. crassa cytoplasm lines indicated the difference of salt tolerance in varying degree; the difference of cytoplasm effect among different nucleoplasm combinations showed certain nucleoplasm interaction relation. The salt tolerance of (Ae. crassa)-jian 26 was stronger than that other tested alloplasmic lines. The result demonstrated that at recovering date and at mature period indicated salt tolerance of alloplasmic lines was not only stronger than its nuclear parent but also over control variety. As compared with common wheat, lines having strong salt tolerance were more proportions in tested alloplasmic lines. The study of alloplasmic wheat should be significant for breeding salt tolerance wheat.

Cytoplasm↗

PubMed2000

Analysis by two-dimensional electrophoresis of the effect of salt stress on the polypeptide patterns in roots of a salt-tolerant and a salt-sensitive cultivar of wheat.

The effect of salt stress on the polypeptide levels in roots of two wheat (Triticum durum) cultivars with different sensitivity to NaCl (cv. Ben Bachir, sensitive; cv. Chili, tolerant), was examined by two-dimensional polyacrylamide gel electrophoresis. Blue-stained gels were analyzed by visual inspection to identify changes that resulted when seedlings were grown in the presence of 200 mM NaCl for four days. Although the protein patterns for control and salt-stressed seedlings were qualitatively similar, the net synthesis of a 26 kDa polypeptide was significantly changed. This observation was mainly noticeable in the more tolerant cultivar. With the intention of identifying its function, the NH2-terminal of this polypeptide was sequenced. A 20 amino acid sequence was obtained and compared to sequences available in different databases. Possible roles of this polypeptide, depending on the homologies of its amino acid sequence with known proteins, in salinity tolerance are discussed.

Electrophoresis, Gel, Two-Dimensional↗

PubMed2001

Treatment of hypersaline-containing wastewater with salt-tolerant microorganisms.

Two salt-tolerant bacteria were isolated from soil samples to treat a high-salt-content wastewater from a pickled plum production plant. The strains, which were identified as Staphylococcus sp. and Bacillus cereus, grew well in a medium containing 0 to 15% NaCl. When wastewater in a flask was treated with the strains for 72 h, the COD removal was about 70%, and this was increased to about 90% when they were used in a pilot plant (working volume 1 m3) in a batch culture carried out for 7 d. The Staphylococcus sp. and Bacillus cereus strains occupied almost all of the pilot plant, in which they were present in a ratio of 3:1 (at 23-27 degrees C).

Journal Article↗

PubMed1993

Characterization of the Early Stages of Genetic Salt-Stress Responses in Salt-Tolerant Lophopyrum elongatum, Salt-Sensitive Wheat, and Their Amphiploid.

Eleven unique cDNA clones corresponding to genes showing enhanced mRNA accumulation in the early stages of salt stress (early salt stress induced, ESI) were previously isolated. The accumulation of these mRNAs in Lophopyrum elongatum (Host) A. Love, salt-sensitive wheat (Triticum aestivum L.), and their amphiploid is compared. The accumulation of ESI mRNAs was much greater in the L. elongatum roots than in the shoots. Additionally, mRNA accumulation in the roots of the three genotypes showed a biphasic response. The first phase occurred within a few hours after the onset of stress and had a large osmotic shock component, as indicated by induction of the accumulation of these mRNAs by a nonsaline osmoticum. The ion-specific component, however, also played a role. External Ca2+ reduced this response. The second phase was characterized by either constantly elevated mRNA levels or gradually increasing mRNA levels. The same biphasic response was elicited by exogenous abscisic acid (ABA). The response of all mRNAs to ABA closely approximated the response to 250 mM NaCl treatment in all three genotypes. The differences among the three genotypes in response to NaCl and ABA treatments were largely confined to the first phase of the response, in which mRNA levels were highest in L. elongatum and lowest in wheat. The levels of ESI mRNAs in the amphiploid closely approximated levels calculated on the basis of the doses of wheat and L. elongatum genomes in the amphiploid, which indicated an additive contribution of the genomes to early salt stress response in the amphiploid. The inducer of the ESI mRNA accumulation in response to NaCl and other osmotica is produced in the stressed roots and shows only minor, if any, translocation. A putative candidate for this inducer is root ABA.

Journal Article↗

PubMed1990

Patch clamp studies on root cell vacuoles of a salt-tolerant and a salt-sensitive plantago species : regulation of channel activity by salt stress.

Plantago media L. and Plantago maritima L. differ in their strategy toward salt stress, a major difference being the uptake and distribution of ions. Patch clamp techniques were applied to root cell vacuoles to study the tonoplast channel characteristics. In both species the major channel found was a 60 to 70 picosiemens channel with a low ion selectivity. The conductance of this channel for Na(+) was the same as for K(+), P(K) (+)/P(Na) (+) = 1, whereas the cation/anion selectivity (P(K) (+)/P(c1) (-)) was about 5. Gating characteristics were voltage and calcium dependent. An additional smaller channel of 25 picosiemens was present in P. maritima. In the whole vacuole configuration, the summation of the single channel currents resulted in slowly activated inward currents (t((1/2)) = 1.2 second). Inwardly directed, ATP-dependent currents could be measured against a DeltapH gradient of 1.5 units over the tonoplast. This observation strongly indicated the physiological intactness of the used vacuoles. The open probability of the tonoplast channels dramatically decreased when plants were grown on NaCl, although single channel conductance and selectivity were not altered.

Journal Article↗

PubMed2006

Analysis of the physiological mechanism of salt-tolerant transgenic rice carrying a vacuolar Na+/H + antiporter gene from Suaeda salsa.

Salt stress is one of the most serious factors limiting the productivity of agricultural crops. Increasing evidence has demonstrated that vacuolar Na+/H+ antiporters play a crucial role in plant salt tolerance. In the present study, we expressed the Suaeda salsa vacuolar Na+/H+ antiporter SsNHX1 in transgenic rice to investigate whether this can increase the salt tolerance of rice, and to study how overexpression of this gene affected other salt-tolerant mechanisms. It was found that transgenic rice plants showed markedly enhanced tolerance to salt stress and to water deprivation compared with non-transgenic controls upon salt stress imposition under outdoor conditions. Measurements of ion levels indicated that K+, Ca2+ and Mg2+ contents were all higher in transgenic plants than in non-transformed controls. Furthermore, shoot V-ATPase hydrolytic activity was dramatically increased in transgenics compared to that of non-transformed controls under salt stress conditions. Physiological analysis also showed that the photosynthetic activity of the transformed plants was higher whereas the same plants had reduced reactive oxygen species generation. In addition, the soluble sugar content increased in the transgenics compared with that in non-transgenics. These results imply that up-regulation of a vacuolar Na+/H+ antiporter gene in transgenic rice might cause pleiotropic up-regulation of other salt-resistance-related mechanisms to improve salt tolerance.

Adaptation, Physiological↗

PubMed2001

Relationships between growth and gas exchange characteristics in some salt-tolerant amphidiploid Brassica species in relation to their diploid parents.

Relationships between growth and different gas exchange characteristics of two amphidiploid salt tolerant species, Brassica napus, and B. carinata with respect to their salt sensitive parents, B. oleracea, and B. nigra were investigated. Twenty three-day old plants of these four species along with those of another amphidiploid moderately salt tolerant B. juncea (developed by hybridization of diploids, B. campestris and B. nigra), and a diploid moderately salt tolerant, B. campestris, were subjected for 28 days to salinized sand culture containing 0, 100 or 200 mol NaCl m(-3) in Hoagland's nutrient solution. The species B. napus and B. carinata produced significantly greater shoot fresh and dry matters than their parents under saline conditions. A close association was found between growth, and assimilation rate for all species differing in degree of salt tolerance. Stomatal conductance (g(s)) was reduced due to salt stress in all species but this variable had no significant correlation with assimilation rate (A). However, the amphidiploid salt tolerant species, B. napus and B. carinata had significantly greater photosynthetic rate, water use efficiency (A/E), intrinsic water use efficiency (A/g(s)) than those of their diploid parents. In conclusion, high salt tolerance of the two amphidiploid species, B. napus and B. carinata was associated with a high assimilation rate, water use efficiency and intrinsic water use efficiency but there was little association of the tolerance of these species with stomatal conductance, leaf water potential or transpiration rate (E).

Journal Article↗

PubMed1996

Salt tolerance in plants and microorganisms: toxicity targets and defense responses.

Salt tolerance of crops could be improved by genetic engineering if basic questions on mechanisms of salt toxicity and defense responses could be solved at the molecular level. Mutant plants accumulating proline and transgenic plants engineered to accumulate mannitol or fructans exhibit improved salt tolerance. A target of salt toxicity has been identified in Saccharomyces cerevisiae: it is a sodium-sensitive nucleotidase involved in sulfate activation and encoded by the HAL2 gene. The major sodium-extrusion system of S. cerevisiae is a P-ATPase encoded by the ENA1 gene. The regulatory system of ENA1 expression includes the protein phosphatase calcineurin and the product of the HAL3 gene. In Escherichia coli, the Na(+)-H+ antiporter encoded by the nhaA gene is essential for salt tolerance. No sodium transport system has been identified at the molecular level in plants. Ion transport at the vacuole is of crucial importance for salt accumulation in this compartment, a conspicuous feature of halophytic plants. The primary sensors of osmotic stress have been identified only in E. coli. In S. cerevisiae, a protein kinase cascade (the HOG pathway) mediates the osmotic induction of many, but not all, stress-responsive genes. In plants, the hormone abscisic acid mediates many stress responses and both a protein phosphatase and a transcription factor (encoded by the ABI1 and ABI3 genes, respectively) participate in its action.

Drug Tolerance↗

PubMed2003

[Salt tolerance of wild soybeans in Jiangsu and its relation with ionic distribution and selective transportation].

The salt tolerance of 3 wild soybean (Glycine soja) populations was compared with their relative germination and seedling emergence. The results showed that the salt tolerance of Jiangsu wild soybean (JWS) was the strongest. Under NaCl stress, the dry matter accumulation in wild soybean seedlings decreased, root/shoot ratio increased, and these effects were greater in N23232 (salt-sensitive) than in JWS (salt-tolerant). Determinations on the ion contents in different organs indicated that the Na+ content was higher in stem than in other organs, and the accumulation of Na+ and Cl- in roots was significantly more in JWS than in N23232. The contents of these ions in JWS leaves were much less than those in N23232 leaves. There was no significant difference between selective absorptions of K+ and Na+ (ASK, Na) by the two populations, but the selective transportation of K+ and Na+ (TSK, Na) in stem and leaf was much higher in JWS than in N23232, resulted in the higher K+/Na+ ratio in JWS shoots. It is suggested that the main reason for the salt tolerance in salt-tolerant wild soybean was the accumulation of Na+ and Cl- in roots and stems and the higher selective transportation of K+ from root to shoot.

Germination↗

PubMed2006

Expressions of OsHKT1, OsHKT2, and OsVHA are differentially regulated under NaCl stress in salt-sensitive and salt-tolerant rice (Oryza sativa L.) cultivars.

Under NaCl-dominated salt stress, the key to plant survival is maintaining a low cytosolic Na(+) level or Na(+)/K(+) ratio. The OsHKT1, OsHKT2, and OsVHA transporter genes might play important roles in maintaining cytosolic Na(+) homeostasis in rice (Oryza sativa L. indica cvs Pokkali and BRRI Dhan29). Upon NaCl stress, the OsHKT1 transcript was significantly down-regulated in salt-tolerant cv. Pokkali, but not in salt-sensitive cv. BRRI Dhan29. NaCl stress induced the expression of OsHKT2 and OsVHA in both Pokkali and BRRI Dhan29. In cv. Pokkali, OsHKT2 and OsVHA transcripts were induced immediately after NaCl stress. However, in cv. BRRI Dhan29, the induction of OsHKT2 was quite low and of OsVHA was low and delayed, compared with that in cv. Pokkali. OsHKT2 and OsVHA induction mostly occurred in the phloem, in the transition from phloem to mesophyll cells, and in the mesophyll cells of the leaves. The vacuolar area in cv. Pokkali did not change under either short- (5-10 min) or long-term (24 h) salt stress, although it significantly increased 24 h after the stress in cv. BRRI Dhan29. When expressional constructs of VHA-c and VHA-a with YFP and CFP were introduced into isolated protoplasts of cvs Pokkali and BRRI Dhan29, the fluorescence resonance energy transfer (FRET) efficiency between VHA-c and VHA-a upon salt stress decreased slightly in cv. Pokkali, but increased significantly in cv. BRRI Dhan29. The results suggest that the salt-tolerant cv. Pokkali regulates the expression of OsHKT1, OsHKT2, and OsVHA differently from how the salt-sensitive cv. BRRI Dhan29 does. Together, these proteins might confer salt tolerance in Pokkali by maintaining a low cytosolic Na(+) level and a correct ratio of cytosolic Na(+)/K(+).

Cation Transport Proteins↗

PubMed2006

Adaptation of salt-tolerant Myxococcus strains and their motility systems to the ocean conditions.

More and more studies have indicated that myxobacteria are able to live in seawater conditions, which, however, can decrease the fruiting body formation ability and also the adventurous (A) and social (S) motility systems of the myxobacteria. To learn the adaptation mechanism of the salt-tolerant myxobacteria to marine conditions, we analyzed 10 salt-tolerant Myxococcus strains of their fruiting body formation and motility. The isolates were from marine samples and possessed different levels of salt tolerance. They had the dual motility system and formed fruiting bodies in the presence of suitable seawater concentrations. Some high salt-tolerant strains even lost their fruiting abilities in the absence of seawater. In response to the presence of seawater, the S-motility was found to be increased in the high salt-tolerants but decreased in the low salt-tolerants. The A-motility, on the other hand, was observed in all the salt-tolerant Myxococcus strains, but increased or decreased in response to the presence of seawater. Perceived shifts of fruiting body formation abilities and motilities discovered in the salt-tolerant Myxococcus strains suggested an ecological adaptation of myxobacterial social behaviors to the marine environments.

Adaptation, Physiological↗