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PubMed2003

Salinity stress-tolerant and -sensitive rice (Oryza sativa L.) regulate AKT1-type potassium channel transcripts differently.

In the indica rice (Oryza sativa L.) a cDNA was characterized that encoded OsAKT1 homologous to inward-rectifying potassium channels of the AKT/KAT subfamily. Transcript analysis located OsAKT1 predominantly in roots with low abundance in leaves. Cell-specificity of OsAKT expression was analyzed by in situ hybridizations. In roots, strongest signals were localized to the epidermis and the endodermis, whereas lower transcript levels were detected in cells of the vasculature and the cortex. In leaves, expression was detected in xylem parenchyma, phloem, and mesophyll cells. Transcriptional regulation and cell specificity of OsAKT1 during salt stress was compared in rice lines showing different salinity tolerance. In the salt-tolerant, sodium-excluding varieties Pokkali and BK, OsAKT1 transcripts disappeared from the exodermis in plants treated with 150 mM NaCl for 48 h but OsAKT1 transcription was not repressed in these cells in the salt-sensitive, sodium-accumulating variety IR29. Significantly, all lines were able to maintain potassium levels under sodium stress conditions, while sodium concentrations in the leaves of IR29 increased 5-10-fold relative to the sodium concentration in BK or Pokkali. The divergent, line-dependent and salt-dependent, regulation of this channel does not significantly affect potassium homeostasis under salinity stress. Rather, repression in Pokkali/BK and lack of repression in IR29 correlate with the overall tolerance character of these lines.

Amino Acid Sequence↗
PubMed2003

Salt tolerance-related protein STO binds to a Myb transcription factor homologue and confers salt tolerance in Arabidopsis.

Regulating the intracellular Na+/K+ ratio is an essential process for salinity tolerance. The yeast mutant, can, which is deficient in calcineurin, can not grow on medium containing Na+ because it is unable to regulate the intracellular Na+/K+ ratio. Expression of the STO gene of Arabidopsis thaliana in the can mutant complements the salt-sensitive phenotype. A protein of Arabidopsis, an H-protein promoter binding factor (HPPBF-1), that binds to STO protein was isolated. HPPBF-1 cDNA has a sequence encoding a Myb DNA binding-motif and its gene expression is induced by salt stress. Furthermore, HPPBF-1 protein is localized in the nucleus. Although, the expression level of STO is not induced under salt-stress conditions, overexpression of STO in a transgenic Arabidopsis plant gave it a higher salt tolerance than was observed in the wild type. When STO transgenic plants and wild-type plants were subjected to salt stress, root growth was increased by 33-70% in the transgenic plants under salt stress. These results suggest that STO is involved in salt-stress responses in Arabidopsis.

Adaptation, Physiological↗
PubMed2002

Can the nitrogenous composition of xylem sap be used to assess salinity stress in Casuarina glauca?

It is predicted that dryland salinity will affect up to 17 Mha of the Australian landscape by 2050, and therefore, monitoring the health of tree plantings and remnant native vegetation in saline areas is increasingly important. Casuarina glauca Sieber ex Spreng. has considerable salinity tolerance and is commonly planted in areas with a shallow, saline water table. To evaluate the potential of using the nitrogenous composition of xylem sap to assess salinity stress in C. glauca, the responses of trees grown with various soil salinities in a greenhouse were compared with those of trees growing in field plots with different water table depths and groundwater salinities. In the greenhouse, increasing soil salinity led to increased allocation of nitrogen (N) to proline and arginine in both stem and root xylem sap, with coincident decreases in citrulline and asparagine. Although the field plots were ranked as increasingly saline-based on ground water salinity and depth-only the allocation of N to citrulline differed significantly between the field plots. Within each plot, temporal variation in the composition of the xylem sap was related to rainfall, rainfall infiltration and soil salinity. Periods of low rainfall and infiltration and higher soil salinity corresponded with increased allocation of N to proline and arginine in the xylem sap. The allocation of N to citrulline and asparagine increased following rainfall events where rain was calculated to have infiltrated sufficiently to decrease soil salinity. The relationship between nitrogenous composition of the xylem sap of C. glauca and soil salinity indicates that the analysis of xylem sap is an effective method for assessing changes in salinity stress in trees at a particular site over time. However, the composition of the xylem sap proved less useful as a comparative index of salinity stress in trees growing at different sites.

Arginine↗
PubMed2006

Increasing salt tolerance in the tomato.

In this paper, a number of strategies to overcome the deleterious effects of salinity on plants will be reviewed; these strategies include using molecular markers and genetic transformation as tools to develop salinity-tolerant genotypes, and some cultural techniques. For more than 12 years, QTL analysis has been attempted in order to understand the genetics of salt tolerance and to deal with component traits in breeding programmes. Despite innovations like better marker systems and improved genetic mapping strategies, the success of marker-assisted selection has been very limited because, in part, of inadequate experimental design. Since salinity is variable in time and space, experimental design must allow the study of genotype x environment interaction. Genetic transformation could become a powerful tool in plant breeding, but the growing knowledge from plant physiology must be integrated with molecular breeding techniques. It has been shown that the expression of several transgenes promotes a higher level of salt tolerance in some species. Despite this promising result, the development of a salt-tolerant cultivar by way of transgenesis has still not been achieved. Future directions in order to overcome the present limitations are proposed. Three cultural techniques have proved useful in tomato to overcome, in part, the effects of salinity: treatment of seedlings with drought or NaCl ameliorates the adaptation of adult plants to salinity; mist applied to tomato plants grown in Mediterranean conditions improves vegetative growth and yield in saline conditions; and grafting tomato cultivars onto appropriate rootstocks could reduce the effects of salinity.

Breeding↗
PubMed2005

Possible involvement of some secondary metabolites in salt tolerance of sugarcane.

Accumulation of toxic ions in plant tissues modulates the levels of primary and secondary metabolites, which may be related to salinity tolerance. In this study two sugarcane clones, CP-4333 (tolerant) and HSF-240 (sensitive), were exposed to salinity levels at the formative stage, and evaluated three times at 10-day intervals. Although net rate of photosynthesis (Pn), leaf area, length and dry weight of shoots were decreased in both clones, the CP-4333 showed less reduction compared to HSF-240. Both clones displayed a general tendency to accumulate Na+ and Cl- and little K+, though CP-4333 accumulated less Na+ and more K+ compared to HSF-240, and thus showed a higher K+:Na+ ratio. The carotenoid (CAR) content remained steady, while total chlorophyll (CHL) was slightly reduced in the tolerant clone and significantly reduced in HSF-240. In contrast, soluble phenolics (PHE), anthocyanins (ANT) and flavones (FLA) levels were 2.5, 2.8 and 3.0 times greater in CP-4333 in comparison with HSF-240. The decrease in Pn and most secondary metabolites demonstrated by the sensitive clone, but not evidenced in the tolerant clones, suggest that the presence of those metabolites is related to increased salt tolerance of sugarcane. The increased synthesis of PHE, ANT and FLA seems to protect sugarcane from ion-induced oxidative stress, probably due to a common structural skeleton, the phenyl group, of those metabolites. CAR, as components of the light harvesting center (LHC) and biosynthesized in chloroplasts, may confer resistance to this organelle. The PHE, ANT and FLA synthesized in the cytosol may protect cells from ion-induced oxidative damage by binding the ions and thereby showing reduced toxicity on cytoplasmic structures.

Ion Transport↗
PubMed2002

Effect of saline intake on water flux and osmotic homeostasis in Pekin ducks (Anas platyrhynchos).

The physiological regulation of body water volume and concentration was evaluated in Pekin ducks, Anas platyrhynchos, slowly acclimated to increasingly saline drinking water (six equal 75 mM NaCl increments). Body mass, total body water (TBW), water flux, plasma osmolality (Osm(pl)), and ionic and osmoregulatory hormone concentrations were measured at the end of each increment. The salinity at which each variable deviates from its homeostatic set point was calculated by continuous two-phase linear regression. We hypothesized that, as drinking water salinity increases: (1) body water increases in concentration before it decreases in volume and (2) that regulating variables that help determine homeostatically set values (plasma hormone concentrations and water flux) deviate from values of freshwater ducks at lower drinking water salinities than the variables they regulate (Osm(pl), hematocrit, TBW). Osm(pl) was the first variable for which we could calculate a deviation from its homeostatically controlled value. It increases at much lower drinking water salinity than that at which TBW decreases, supporting our first hypothesis, but not our second hypothesis. We further hypothesized that, because the concentration of Pekin duck salt gland secretion is only slightly higher than that of their drinking water, they increase water flux (drinking) as salinity of drinking water increases, until the latter exceeds the secretion concentration and then they drink less. There was no change in water flux until it decreases when TBW decreases, 329 mM NaCl and 335 mM NaCl, respectively. The results do not support our hypothesis that Pekin ducks increase drinking as the salinity of their drinking water increases, but do indicate that, at tolerable salinities, Pekin ducks maintain body water volume while allowing body water osmolality to increase. At higher salinities, ducks decrease drinking and use body water to get rid of the excess salt.

Acclimatization↗
PubMed2001

Transgenic salt-tolerant tomato plants accumulate salt in foliage but not in fruit.

Transgenic tomato plants overexpressing a vacuolar Na+/H+ antiport were able to grow, flower, and produce fruit in the presence of 200 mM sodium chloride. Although the leaves accumulated high sodium concentrations, the tomato fruit displayed very low sodium content. Contrary to the notion that multiple traits introduced by breeding into crop plants are needed to obtain salt-tolerant plants, the modification of a single trait significantly improved the salinity tolerance of this crop plant. These results demonstrate that with a combination of breeding and transgenic plants it could be possible to produce salt-tolerant crops with far fewer target traits than had been anticipated. The accumulation of sodium in the leaves and not in the fruit demonstrates the utility of such a modification in preserving the quality of the fruit.

Blotting, Western↗
PubMed2004

Transport of the harmful bloom alga Aureococcus anophagefferens by oceangoing ships and coastal boats.

It is well established that cyst-forming phytoplankton species are transported in ships' ballast tanks. However, there is increasing evidence that other phytoplankton species which do not encyst are also capable of surviving ballast transit. These species have alternative modes of nutrition (hetero- or mixotrophy) and/or are able to survive long-term darkness. In our studies of no-ballast-on-board vessels arriving in the Great Lakes, we tested for the presence of the harmful algal bloom species Aureococcus anophagefferens (brown tide) in residual (i.e., unpumpable) ballast water using methods based on the PCR. During 2001, the brown tide organism was detected in 7 of 18 ballast water tanks in commercial ships following transit from foreign ports. Furthermore, it was detected after 10 days of ballast tank confinement during a vessel transit in the Great Lakes, a significant result given the large disparity between the salinity tolerance for active growth of Aureococcus (>22 ppt) and the low salinity of the residual ballast water (approximately 2 ppt). We also investigated the potential for smaller, recreational vessels to transport and distribute Aureococcus. During the summer of 2002, 11 trailered boats from the inland bays of Delaware and coastal bays of Maryland were sampled. Brown tide was detected in the bilge water in the bottoms of eight boats, as well as in one live-well sample. Commercial ships and small recreational boats are therefore implicated as potential vectors for long-distance transport and local-scale dispersal of Aureococcus.

DNA, Ribosomal↗
PubMed2004

Grafting raises the salt tolerance of tomato through limiting the transport of sodium and chloride to the shoot.

With the aim of determining whether grafting could improve salinity tolerance of tomato (Lycopersicon esculentum Mill.), and what characteristics of the rootstock were required to increase the salt tolerance of the shoot, a commercial tomato hybrid (cv. Jaguar) was grafted onto the roots of several tomato genotypes with different potentials to exclude saline ions. The rootstock effect was assessed by growing plants at different NaCl concentrations (0, 25, 50, and 75 mM NaCl) under greenhouse conditions, and by determining the fruit yield and the leaf physiological changes induced by the rootstock after 60 d and 90 d of salt treatment. The grafting process itself did not affect the fruit yield, as non-grafted plants of cv. Jaguar and those grafted onto their own root showed the same yield over time under non-saline conditions. However, grafting raised fruit yield in Jaguar on most rootstocks, although the positive effect induced by the rootstock was lower at 25 mM NaCl than at 50 and 75 mM NaCl. At these higher levels, the plants grafted onto Radja, Pera and the hybrid VolgogradskijxPera increased their yields by approximately 80%, with respect to the Jaguar plants. The tolerance induced by the rootstock in the shoot was related to ionic rather than osmotic stress caused by salinity, as the differential fruit yield responses among graft combinations were mainly related to the different abilities of rootstocks to regulate the transport of saline ions. This was corroborated by the high negative correlation found between fruit yield and the leaf Na(+) or Cl(-) concentrations in salt-treated plants after 90 d of salt treatment. In conclusion, grafting provides an alternative way to enhance salt tolerance, determined as fruit yield, in the tomato, and evidence is reported that the rootstock is able to reduce ionic stress.

Biological Transport, Active↗
PubMed2003

Low salinity residual ballast discharge and exotic species introductions to the North American Great Lakes.

Exotic species introductions to the North American Great Lakes have continued even though ballast water management strategies were implemented in the early 1990s. Overseas vessels that arrive with little or no exchangeable ballast on board have been suspected to be an important source for discharging low salinity ballast containing low salinity tolerant organisms in this region. Residual ballast averaged 18.1+/-13.4 per thousand salinity among 62 samples taken primarily from bottom tanks on 26 vessels that entered the Great Lakes in 1999 and 2000. Sampling of 2-4 tanks each on nine vessels indicated all carried at least one tank of residual ballast of </=5 per thousand salinity. Many of these transits originated from the northeast Atlantic, Mediterranean and Black Sea regions which have been the probable source for many of the more recent introductions to this region.

Biodiversity↗
PubMedDate not supplied

There are high levels of functional and genetic diversity in Oxyrrhis marina.

Oxyrrhis marina, a widely distributed marine protist, is used to model heterotrophic flagellate responses in microbial food webs. Although clonal variability occurs in protists, assessments of intraspecific diversity are rare; such assessments are critical, particularly where species are used as models in ecological studies. To address the extent of intraspecific variation within O. marina, we assessed diversity among 11 strains using 5.8S rDNA and ITS sequences. The 5.8S rDNA and ITS regions revealed high divergence between strains: 63.1% between the most diverse. To compare O. marina diversity relative to other alveolates, 18S rDNA sequences for five strains were analysed with sequences from representatives of the major alveolate groups. 18S rDNA also revealed high divergence in O. marina. Additionally, consistent with phylogenies based on protein coding genes, maximum likelihood analysis indicated that O. marina was monophyletic and ancestral to the dinoflagellates. To assess ecophysiological differences, growth rates of seven O. marina strains were measured at 10 salinities (10-55 per thousand). Two salinity responses occurred: one group achieved highest growth rates at high salinities; the other grew best at low salinities. There was no clear correlation between molecular, ecophysiological, or geographical differences. However, salinity tolerance was associated with habitat type: intertidal strains grew best at high salinities; open-water strains grew best at low salinities. These data indicate the need to examine many strains of a species in both phylogenetic and ecological studies, especially where key-species are used to model ecological processes.

Animals↗
PubMed2004

The crab-eating frog, Rana cancrivora, up-regulates hepatic carbamoyl phosphate synthetase I activity and tissue osmolyte levels in response to increased salinity.

The crab-eating frog Rana cancrivora is one of only a handful of amphibians worldwide that tolerate saline waters. They typically inhabit brackish water of mangrove forests of Southeast Asia, but live happily in freshwater and can be acclimated to 75% seawater (25 ppt) or higher. We report here that after transfer of juvenile R. cancrivora from freshwater (1 ppt) to brackish water (10 -->20 or 20 -->25 ppt; 4-8 d) there was a significant increase in the specific activity of the key hepatic ornithine urea cycle enzyme (OUC), carbamoyl phosphate synthetase I (CPSase I). At 20 ppt, plasma, liver and muscle urea levels increased by 22-, 21-, and 11-fold, respectively. As well, muscle total amino acid levels were significantly elevated by 6-fold, with the largest changes occurring in glycine and beta-alanine levels. In liver, taurine levels were 5-fold higher in frogs acclimated to 20 ppt. There were no significant changes in urea or ammonia excretion rates to the environment. As well, the rate of urea influx (J(in) (urea)) and efflux (J(out) (urea)) across the ventral pelvic skin did not differ between frogs acclimated to 1 versus 20 ppt. Taken together, these findings suggest that acclimation to saline water involves the up-regulation of hepatic urea synthesis, which in turn contributes to the dramatic rise in tissue urea levels. The lack of change in urea excretion rates, despite the large increase in tissue-to-water gradients further indicates that mechanisms must be in place to prevent excessive loss of urea in saline waters, but these mechanisms do not include cutaneous urea uptake. Also, amino acid accumulation may contribute to an overall rise in the osmolarity of the muscle tissue, but relative to urea, the contribution is small.

Amino Acids↗
PubMed2003

Building stress tolerance through over-producing trehalose in transgenic plants.

Trehalose is a rare sugar with unique abilities to protect biomolecules from environmental stresses and is present in many bacteria, fungi and some desiccation-tolerant higher plants. Increasing trehalose accumulation in crop plants could improve drought and salinity tolerance. Transgenic plants have been developed with trehalose biosynthetic genes--a recent study on the stress-inducible overexpression of the bifunctional TPSP fusion gene in transgenic rice could offer novel strategies for improving abiotic stress tolerance in crop plants.

Climate↗
PubMed1999

Salt tolerance conferred by overexpression of a vacuolar Na+/H+ antiport in Arabidopsis.

Agricultural productivity is severely affected by soil salinity. One possible mechanism by which plants could survive salt stress is to compartmentalize sodium ions away from the cytosol. Overexpression of a vacuolar Na+/H+ antiport from Arabidopsis thaliana in Arabidopsis plants promotes sustained growth and development in soil watered with up to 200 millimolar sodium chloride. This salinity tolerance was correlated with higher-than-normal levels of AtNHX1 transcripts, protein, and vacuolar Na+/H+ (sodium/proton) antiport activity. These results demonstrate the feasibility of engineering salt tolerance in plants.

Arabidopsis↗
PubMed1989

Increased neuropeptide-converting enzyme activities in cerebrospinal fluid of opiate-tolerant rats.

Rats were given a continuous subcutaneous infusion at constant rate with either morphine, the opioid agonist/antagonist analgesic dezocine or saline. Tolerance to the antinociceptive effect of morphine or dezocine was complete on day 8, when cisterna magnum cerebrospinal fluid (CSF) was sampled under anesthesia. The activity of the enzymes cleaving dynorphin A (DCE) and substance P (SPE) was measured in the CSF. It was found that the animals treated with morphine had a 2- to 3-fold increase in both DCE and SPE activities. The animals treated with dezocine showed a similar increase in the activity of DCE, whereas SPE did not significantly change. These enzymes may therefore play a role in the development of tolerance to opioid analgesic drugs. The experiments show that chronic opioid treatment affects peptidergic mechanisms.

Animals↗
PubMed2026

Genome-wide identification of the Glutathione Peroxidase (GPX) gene family in Taxodium distichum and functional characterization of TdGPX9 in enhancing salt tolerance.

This study systematically identified 10 TdGPX genes in Taxodium distichum, demonstrating that the nucleocytoplasmic-localized TdGPX9 plays a pivotal role in salt stress response. Overexpression of TdGPX9 significantly enhances salt tolerance by strengthening the antioxidant defense system and improving root system plasticity under stress. Taxodium distichum is a premier coniferous species renowned for its exceptional waterlogging and salinity tolerance, serving as a vital forest resource for coastal afforestation and wetland ecological restoration. Within the physiological framework of plant stress resistance, the glutathione peroxidase (GPX) family represents a cornerstone of the antioxidant enzymatic system, playing a critical role in scavenging reactive oxygen species and maintaining cellular redox homeostasis. In this study, 10 TdGPX genes were identified via a comprehensive genome-wide analysis and mapped across eight chromosomes. These genes possess a highly conserved Thioredoxin_like domain, with structural and motif analyses revealing a well-maintained arrangement of conserved motifs within each subgroup. The promoter analysis identified a sophisticated regulatory network enriched with cis-acting elements responsive to light, phytohormones, and abiotic stresses, suggesting their integration into diverse signaling pathways. Expression profiling across various tissues and embryonic developmental stages further highlighted the versatile roles of TdGPX members in plant growth and organogenesis. Notably, qRT-PCR analysis identified the nucleocytoplasmic-localized TdGPX9 as a primary respondent to salinity. Functional validation demonstrated that TdGPX9 overexpression significantly enhances salt tolerance in transgenic Arabidopsis and T. distichum callus by strengthening the antioxidant defense system. Furthermore, TdGPX9 promoted root system plasticity under stress, as evidenced by increased lateral root density. These findings provide a systematic basis for understanding the redox-regulatory mechanisms in baldcypress and offer vital genetic resources for improving forest resilience in coastal wetland ecosystems.

Salt Tolerance↗
PubMed2006

Ectopic expression of ThCYP1, a stress-responsive cyclophilin gene from Thellungiella halophila, confers salt tolerance in fission yeast and tobacco cells.

The halophyte Thellungiella halophila (salt cress) is an ideal model system for studying the molecular mechanisms of salinity tolerance in plants. Herein, we report the identification of a stress-responsive cyclophilin gene (ThCYP1) from T. halophila, using fission yeast as a functional system. The expression of ThCYP1 is highly inducible by salt, abscisic acid (ABA), H(2)O(2) and heat shock. Ectopic overexpression of the ThCYP1 gene enhance the salt tolerance capacity of fission yeast and tobacco (Nicotiana tabacum L.) cv. Bright Yellow 2 (BY-2) cells significantly. ThCYP1 is expressed constitutively in roots, stems, leaves and flowers, with higher expression occurring in the roots and flowers. The ThCYP1 proteins are distributed widely within the cell, but are enriched significantly in the nucleus. The present results suggest that ThCYP1 may participate in response to stresses in the salt cress, perhaps by regulating appropriate folding of certain stress-related proteins, or in the signal transduction processes.

Abscisic Acid↗
PubMed2004

Ectoine accumulation in Brevibacterium epidermis.

As a halotolerant bacterial species, Brevibacterium epidermis DSM 20659 can grow at relatively high salinity, tolerating up to 2 M NaCl. It synthesizes ectoine and the intracellular content increases with the medium salinity, with a maximum of 0.14 g ectoine/g CDW at 1 M NaCl. Sugar-stressed cells do not synthesize ectoine. Ectoine synthesis is also affected by the presence of external osmolytes. Added betaine is taken up and completely replaced ectoine, while L-proline is only temporarily accumulated after which ectoine is synthesized. The strain can metabolize ectoine; L-glutamate is a better carbon source for ectoine synthesis than L-aspartate.

Amino Acids, Diamino↗