Exclusion Of Na Research Articles

Assessment of variation among cultivated wheat species for plant nutrient strata under salinity conditions

Six wheat genotypes, two each of bread wheat (UAS BW-13897 and LBPY 2014-5), Triticum durum (GW 2010-679 and UAS DW-31403) andT. dicoccum (DIC 99 and DIC 26) were grown under natural saline and control conditions to observe the existence of ion discrimination,ion selectivity amenable to ion regulation and ion interactions among them. Bread wheat genotype, UAS BW-13897 showed a highK+ and K+/Na+ ratio at the harvesting stage under saline condition indicating its high salt tolerance. Contrary to it, T. durum genotype,UAS DW-31403 was found to be highly salt-sensitive due to its low K+/Na+ ratio and high Na+ absorption. Bread wheat genotypes werefound most salt-tolerant due to better exclusion of Na+ salt, with negligible reduction in grain yield, spike length, SPAD and numberof grains per spike. The salt exclusion was found less apparent in T. durum and T. dicoccum wheat likely due to the absence of the Dgenome and Kna1 gene, which is present in bread wheat and not in the two tetraploid species. Durum wheat was observed to be mostsensitive with low salt exclusion capacity, whereas T. dicoccum wheat was found intermediate between bread and durum wheat withmedium salt exclusion capacity. The study revealed a difference in type and level of salt tolerance in different species and genotypesthat established high Na+ salt exclusion capacity as one of the important selection criteria for salt tolerance.

English

This study focused on the improving effect of external application of calcium and potassium on growth, ions and organic solutes accumulation in tossa jute plants grown under salt stress. Young plants were subjected in pots to ten treatments including the control without NaCl, 120 mM NaCl and a combination of 120 mM NaCl and an addition of 40 or 60 mM CaSO4, CaCl2, K2SO4 or KNO3. Plant growth, sodium, potassium, proline and soluble sugars contents were determined after two weeks. Results revealed that only the external application of CaSO4 and K2SO4 at 40 mM significantly improved the growth reduction induced by NaCl followed by CaCl2; whereas at 60 mM, only CaSO4 induced similar changes in plant growth. Only, the exogenous application of calcium at 40 mM induced a significant decrease (p<0.05) in the Na+ content and a significant increase (p<0.001) of the K+/Na+ ratio of leaves in comparison with salt stressed plants, while the two forms of calcium and K2SO4 induced a significant increase (p=0.05) in the K+ content. CaSO4 had the best improving effects on plants growth under salt stress, followed by K2SO4 and CaCl2 at 40 mM. This improving effect is due to a better exclusion of Na+ from the leaves, the maintenance of a high ionic selectivity ratio K/Na and/or a better accumulation of K+.   Key words: Corchorus olitorius, sodium, potassium, calcium sulphate, calcium chloride, potassium sulphate, potassium nitrate, proline, soluble sugars.&nbsp

An overview of salinity stress, mechanism of salinity tolerance and strategies for its management in cotton.

Salinity stress is one of the primary threats to agricultural crops resulting in impaired crop growth and development. Although cotton is considered as reasonably salt tolerant, it is sensitive to salt stress at some critical stages like germination, flowering, boll formation, resulting in reduced biomass and fiber production. The mechanism of partial ion exclusion (exclusion of Na+ and/or Cl–) in cotton appears to be responsible for the pattern of uptake and accumulation of harmful ions (Na+ and Cl) in tissues of plants exposed to saline conditions. Maintaining high tissue K+/Na+ and Ca2+/Na+ ratios has been proposed as a key selection factor for salt tolerance in cotton. The key adaptation mechanism in cotton under salt stress is excessive sodium exclusion or compartmentation. Among the cultivated species of cotton, Egyptian cotton (Gossypium barbadense L.) exhibit better salt tolerance with good fiber quality traits as compared to most cultivated cotton and it can be used to improve five quality traits and transfer salt tolerance into Upland or American cotton (Gossypium hirsutum L.) by interspecific introgression. Cotton genetic studies on salt tolerance revealed that the majority of growth, yield, and fiber traits are genetically determined, and controlled by quantitative trait loci (QTLs). Molecular markers linked to genes or QTLs affecting key traits have been identified, and they could be utilized as an indirect selection criterion to enhance breeding efficiency through marker-assisted selection (MAS). Transfer of genes for compatible solute, which are an important aspect of ion compartmentation, into salt-sensitive species is, theoretically, a simple strategy to improve tolerance. The expression of particular stress-related genes is involved in plant adaptation to environmental stressors. As a result, enhancing tolerance to salt stress can be achieved by marker assisted selection added with modern gene editing tools can boost the breeding strategies that defend and uphold the structure and function of cellular components. The intent of this review was to recapitulate the advancements in salt screening methods, tolerant germplasm sources and their inheritance, biochemical, morpho-physiological, and molecular characteristics, transgenic approaches, and QTLs for salt tolerance in cotton.

Sodium Accumulation in Infected Cells and Ion Transporters Mistargeting in Nodules of Medicago truncatula: Two Ugly Items That Hinder Coping with Salt Stress Effects.

The maintenance of intracellular nitrogen-fixing bacteria causes changes in proteins’ location and in gene expression that may be detrimental to the host cell fitness. We hypothesized that the nodule’s high vulnerability toward salt stress might be due to alterations in mechanisms involved in the exclusion of Na+ from the host cytoplasm. Confocal and electron microscopy immunolocalization analyses of Na+/K+ exchangers in the root nodule showed the plasma membrane (MtNHX7) and endosome/tonoplast (MtNHX6) signal in non-infected cells; however, in mature infected cells the proteins were depleted from their target membranes and expelled to vacuoles. This mistargeting suggests partial loss of the exchanger’s functionality in these cells. In the mature part of the nodule 7 of the 20 genes encoding ion transporters, channels, and Na+/K+ exchangers were either not expressed or substantially downregulated. In nodules from plants subjected to salt treatments, low temperature-scanning electron microscopy and X-ray microanalysis revealed the accumulation of 5–6 times more Na+ per infected cell versus non-infected one. Hence, the infected cells’ inability to withstand the salt may be the integral result of preexisting defects in the localization of proteins involved in Na+ exclusion and the reduced expression of key genes of ion homeostasis, resulting in premature senescence and termination of symbiosis.

Comparative genetic, biochemical and physiological analysis of sodium and chlorine in wheat.

Plant with a great diversity shows several responses towards the biotic and abiotic stresses. Among these abiotic stresses, salinity is the main damaging factor as it reduces the yield of wheat plant with moderate salt tolerance. For its survival, plant undergoes through some genetic, biochemical and physiological changes to tackle the stress. This review mainly describes the conditions where various ions present in the soil, especially sodium and chlorine, enter into the plant and the genes or proteins involved with survival mechanism against the damage in plants. Salt stress causes alteration in enzymatic activity and Photosynthesis, oxidative stress, damage of cellular structure and components and ionic imbalance. Ion toxicity stress occur due to accumulation of excessive sodium ion and chloride ion. Transcriptional factors TaPIMP, TaSRG and TaMYBsdu 1 play key role in gene expression mechanism to overcome the stress. High affinity potassium transporter gene family is responsible for salt tolerance in wheat plant. HKT1;4 and HKT1;5 genes are responsible for Na exclusion in Triticum monococcum. Forty QTLs were found with the marker assisted selection in bread wheat for salinity tolerance and some morphological traits, 5 QTLs were related to sodium ion exclusion. In bread wheat, salt stress tolerance mechanism is mainly an exclusion of Na+ ions but also include K+ ion concentration. The salinity tolerant germplasm MW#293 provides an opportunity for the development of future salinity tolerant bread wheat.

Transgenic Expression of Prunus persica Salt Overly Sensitive 2 (PpSOS2) in the atsos2 Mutant Imparts Salt Tolerance in Arabidopsis

Salinity is one of the main environmental stresses that negatively affect crop productivity. Almond trees are sensitive to salt stress; however, salinity-tolerant rootstocks can significantly enhance crop production under saline conditions. This work reports the functional complementation of the Prunus persica Salt Overly Sensitive 2 (PpSOS2) gene from the almond rootstock “Nemaguard” in the Arabidopsis thaliana atsos2 mutant. Two transgenic lines of PpSOS2 developed using constitutive (PpSOS2.OE3.5) and endogenous (PpSOS2NP.2.7) promoters showed significantly higher germination, survival rates, and dry weight than atsos2 under 90 mM NaCl treatment. The atsos2 mutant displayed the inhibition of primary and lateral roots under 50 mM NaCl. The root growth inhibition was restored by PpSOS2 complementation. Both transgenic lines showed a significant decrease in electrolyte leakage compared to atsos2 under 50 mM NaCl. The expression analysis of six K+-rectifying channel genes and a reactive oxygen species-specific gene revealed the differential expression of AtCHX14 and AtCHX13 genes in transgenic lines compared to atsos2 24 h after the 50 mM NaCl treatment. These observations suggest that PpSOS2 modulates and restores salt tolerance in atsos2. Also, in Prunus, the SOS pathway is conserved, suggesting that the exclusion of Na+ is an important component trait for salt tolerance.

Salt tolerance of seven genotypes of zoysiagrass (<i>Zoysia</i> spp.)

Seven zoysiagrass genotypes were evaluated for salt tolerance in a greenhouse study. The plant materials included <italic>Zoysia matrella</italic> 'Diamond', <italic>Z. japonica</italic> 'Palisades', three <italic>Z</italic>. <italic>matrella</italic> × <italic>Z. japonica</italic> hybrids DALZ 1701, DALZ 1713, and 'Innovation', and two <italic>Z.</italic> <italic>minima</italic> × <italic>Z. matrella</italic> hybrids (DALZ 1309 and 'Lazer'). Treatments included a control (nutrient solution) and two saline treatments representing moderate and high salt levels. The electrical conductivity (EC) was 1.3 dS m⁻¹ for control and moderate (EC5) and high salinity (EC10) were 5.0 and 10.0 dS m⁻¹, respectively. At the end of eight-week treatments, the relative (percent control) shoot dry weight (DW) was greatest in 'Diamond' in EC10, and the relative root DW was greatest in DALZ 1309 in EC5. A cluster analysis based on the relative tissue dry weight identified 'Diamond', DALZ 1309, and DALZ 1713 as the most salt tolerant genotypes. Additionally, the green leaf area (GLA) index of 'Diamond' and DALZ 1713 were 98.8% and 100%, respectively, indicating excellent visual appearance under high salt levels. Bi-weekly clipping DW showed that ‘Diamond’ continued to produce biomass throughout the duration of the study under the EC10 treatment. Sodium (Na⁺) and chloride (Cl⁻) content in the shoot tissue of the seven turfgrass genotypes indicated that lower concentrations corresponded to greater salt tolerance indicating exclusion of Na⁺ and Cl⁻ from the shoot tissue. Taken together, the genotypes 'Diamond' and DALZ 1713 were determined to be the most salt tolerant and recommended for use in areas with high soil or water salinity.

Paraburkholderia sp. GD17 improves rice seedling tolerance to salinity

The plant growth promoting rhizobacteria have been extensively implicated in plant responses to changing environments. However, the action mechanisms still need to be elucidated. This study addressed the effect of Paraburkholderia sp. GD17 on rice seedlings in responses to salt stress. The experiment consisted of GD17-inoculated and non-inoculated plants, with or without NaCl treatment. Physiological and biochemical parameters, and gene expression were analyzed. GD17 efficiently colonized inside roots, and provided a protection against salt stress. Following exposure to 68 mM of NaCl for 48 h, although the accumulation of Na+ was not affected in GD17-inoculated (+ GD17) roots relative to non-inoculated ones, its concentration was substantially reduced in + GD17 shoots. The contents of K and other mineral elements were higher in + GD17 plants. The expression of Na+ and K+ transporter-encoding genes generally presented a higher level in + GD17 plants. The antioxidative defense especially related to the removal of H2O2 was more strongly activated in + GD17 plants. Correspondingly, salt-induced oxidative damage was significantly ameliorated. A substantial increase in proline content and gene expression was observed in + GD17 plants. Additionally, the cell wall invertase-encoding gene displayed a dramatically higher expression level in + GD17 plants. GD17 efficiently improved rice seedling tolerance to salt stress. The possible mechanisms might be associated with the absorption and redistribution of mineral elements, the vacuolar sequestration of Na+ as well as exclusion of Na+, antioxidative defense, the production of proline, and the sucrose catabolism in apoplast.

Digital Phenotyping to Delineate Salinity Response in Safflower Genotypes.

Salinity is a major contributing factor to the degradation of arable land, and reductions in crop growth and yield. To overcome these limitations, the breeding of crop varieties with improved salt tolerance is needed. This requires effective and high-throughput phenotyping to optimize germplasm enhancement. Safflower (Carthamus tinctorius L.), is an underappreciated but highly versatile oilseed crop, capable of growing in saline and arid environments. To develop an effective and rapid phenotyping protocol to differentiate salt responses in safflower genotypes, experiments were conducted in the automated imaging facility at Plant Phenomics Victoria, Horsham, focussing on digital phenotyping at early vegetative growth. The initial experiment, at 0, 125, 250, and 350 mM sodium chloride (NaCl), showed that 250 mM NaCl was optimum to differentiate salt sensitive and tolerant genotypes. Phenotyping of a diverse set of 200 safflower genotypes using the developed protocol defined four classes of salt tolerance or sensitivity, based on biomass and ion accumulation. Salt tolerance in safflower was dependent on the exclusion of Na+ from shoot tissue and the maintenance of K+ uptake. Salinity response identified in glasshouse experiments showed some consistency with the performance of representatively selected genotypes tested under sodic field conditions. Overall, our results suggest that digital phenotyping can be an effective high-throughput approach in identifying candidate genotypes for salt tolerance in safflower.

Contrasting Responses of Guar Genotypes Shed Light on Multiple Component Traits of Salinity Tolerance Mechanisms

Guar (Cyamopsis tetragonoloba (L.) Taub.) is a legume crop, and gum derived from its seeds has various industrial applications. Due to its tolerance to various abiotic stresses, guar can be grown under water-deficit or high-salinity conditions. In this investigation, four diverse guar genotypes that performed at a similar level in field conditions were evaluated in a salinity experiment in the greenhouse lysimeter system. Based on the salt tolerance index (STI) for shoot biomass, root biomass, shoot length, and root length, Matador and PI 268229 were classified as salt-tolerant, and PI 340261 and PI 537281 as salt-sensitive. Leaf Na concentrations were 4- to 5.5-fold higher, and leaf Cl concentrations were 1.6- to 1.9-fold higher in salt-sensitive lines than salt-tolerant lines under salinity. The strong associations between the leaf K concentrations under salinity compared to the control (K-salinity/K-control) ratio and STI for stem and root length advocate higher importance of K-salinity/K-control than total leaf K concentrations. The expression analyses of genes involved in Na+ and Cl− transport revealed the importance of different component traits of salinity tolerance mechanisms, such as the exclusion of Na+/Cl− from the root, sequestration of Cl− in root vacuoles, retrieval of Na+/Cl− from xylem during salinity stress, root-to-shoot Na+/Cl− translocation, and K+-Na+ homeostasis.

Linking diverse salinity responses of 14 almond rootstocks with physiological, biochemical, and genetic determinants

Fourteen commercial almond rootstocks were tested under five types of irrigation waters to understand the genetic, physiological, and biochemical bases of salt-tolerance mechanisms. Treatments included control (T1) and four saline water treatments dominant in sodium-sulfate (T2), sodium-chloride (T3), sodium-chloride/sulfate (T4), and calcium/magnesium-chloride/sulfate (T5). T3 caused the highest reduction in survival rate and trunk diameter, followed by T4 and T2, indicating that Na and, to a lesser extent, Cl were the most toxic ions to almond rootstocks. Peach hybrid (Empyrean 1) and peach-almond hybrids (Cornerstone, Bright’s Hybrid 5, and BB 106) were the most tolerant to salinity. Rootstock’s performance under salinity correlated highly with its leaf Na and Cl concentrations, indicating that Na+ and Cl- exclusion is crucial for salinity tolerance in Prunus. Photosynthetic rate correlated with trunk diameter and proline leaf ratio (T3/T1) significantly correlated with the exclusion of Na+ and Cl-, which directly affected the survival rate. Expression analyses of 23 genes involved in salinity stress revealed that the expression differences among genotypes were closely associated with their performance under salinity. Our genetic, molecular, and biochemical analyses allowed us to characterize rootstocks based on component traits of the salt-tolerance mechanisms, which may facilitate the development of highly salt-tolerant rootstocks.

Effect of different Soil Sodicity levels on growth, yield and Na/k ratio in cotton

The world agriculture is suffering due to development of salinity and poses a major setback in increasing the yield of cotton. The ability of the plant system to maintain low sodium concentration is a critical component for its tolerance to salt affected conditions. The plant Na/K concentration in the plant was studied to understand the cotton crop for their tolerance to different sodicity levels (Different ESP levels) and to assess its effect on yield. The cotton varieties (SVPR 2 and Surabi) and Bt cotton (RCH -20) was tested in the field experiment under different ESP levels. The yield of cotton varieties and Bt cotton was recorded at different ESP levels. The yield was higher in Bt cotton compared to other two verities and the ESP level of 38-41 is fixed as to get 50% yield. This was mainly exclusion of Na in the cotton leads to the lower level of Na/K ratio in the Bt cotton plants than the varieties tested.

Domestication influences morphological and physiological responses to salinity in Brassica oleracea seedlings.

Brassica oleracea cultivars include important vegetable and forage crops grown worldwide, whereas the wild counterpart occurs naturally on European sea cliffs. Domestication and selection processes have led to phenotypic and genetic divergence between domesticated plants and their wild ancestors that inhabit coastal areas and are exposed to saline conditions. Salinity is one of the most limiting factors for crop production. However, little is known about how salinity affects plants in relation to domestication of B. oleracea. The objective of this study was to determine the influence of domestication status (wild, landrace or cultivar) on the response of different B. oleracea crops to salinity, as measured by seed germination, plant growth, water content and mineral concentration parameters at the seedling stage. For this purpose, two independent pot experiments were conducted with six accessions of B. oleracea, including cabbage (group capitata) and kale (group acephala), in a growth chamber under controlled environmental conditions. In both taxonomic groups, differences in domestication status and salt stress significantly affected all major process such as germination, changes in dry matter, water relations and mineral uptake. In the acephala experiment, the domestication × salinity interaction significantly affected water content parameters and shoot Na+ allocation. At early stages of development, wild plants are more succulent than cultivated plants and have a higher capacity to maintain lower Na+ concentrations in their shoots in response to increasing levels of salinity. Different responses of domesticated and cultivated accessions in relation to these traits indicated a high level of natural variation in wild B. oleracea. Exclusion of Na+ from shoots and increasing succulence may enhance salt tolerance in B. oleracea exposed to extreme salinity in the long term. The wild germplasm can potentially be used to improve the salt tolerance of crops by the identification of useful genes and incorporation of these into salinity-sensitive cultivars.

Exogenous Pi supplementation improved the salt tolerance of maize (Zea mays L.) by promoting Na+ exclusion

The mechanism of phosphate (Pi)-mediated salt tolerance in maize is poorly understood. In this study, the effects of Pi (H2PO4−) on the salt tolerance of two contrasting genotypes was investigated in a pot experiment. We discovered that the application of 3 mM Pi could alleviate salt injury caused by 200 mM NaCl. High amounts of compatible solutes and low amounts of reactive oxygen species (ROS) were also observed under Pi application. Consistent with the increased tolerance, the total number of roots and the growth of shoots increased to relieve salt stress. This phenomenon could be associated with the observed increased expression of nitrate transporters. Furthermore, the seedlings presented a negative relationship between sodium (Na+) and Pi (low Na+ content and high Pi content), which is related to the genes ZmNHX1, ZmPHT1;8, and ZmPHT1;9, indicating that the exclusion of Na+ was promoted by high Pi uptake. However, high Na+ and low potassium (K+) efflux were detected in the roots, and these were positively correlated with two K+ transporters. These observations indicate that Na+ exclusion was directly induced by high K+ retention rather than Pi absorption. We conclude that maize salt tolerance increased in response to Pi application by promoting Na+ exclusion.

Leaf gas exchange physiology and ion homeostasis of oilseed rape ( Brassica napus L.) under Mediterranean conditions: Associations with seed yield and quality

Abstract For two growth seasons, four oilseed rape cultivars were tested in two locations under Mediterranean conditions in order to identify leaf physiological [gas exchange and related traits, chlorophyll content (assessed by SPAD), carbon isotope discrimination (Δ), canopy area index] and elemental traits (K, Na, Ca, Mg, their sum and ratios) related to yield and quality. Determinations took place at one vegetative (stem elongation-BBCH 33 stage) and two reproductive stages (50% flowering of the central inflorescence-BBCH 65 stage and end of flowering-BBCH 69 stage). Yield and seed quality were strongly affected by growth season and location; cultivars differed only in quality traits [seed oil concentration (Oil), protein concentration (Prot), glucosinolates in seed meal (Glu), and erucic acid concentration (Eru)]. Exempting SPAD, cultivars did not also differ in physiological traits and this is a possible reason for the lack of significant differentiation in yield. Cultivars that excluded Na more effectively were those with higher SPAD. Across growth seasons and locations, heavy-textured soil, lower temperatures and high precipitation in winter resulted in higher yield and quality. Larger canopy area at BBCH 65 stage led to higher oil yield (OY). In contrast, higher CO 2 assimilation rate (at BBCH 65 stage) and SPAD (BBCH 65 and 69 stages) were indicative of stressful conditions (high temperatures and low rainfall) since these two traits were negatively correlated with OY. Moreover, SPAD at BBCH 65 stage was also negatively correlated with Oil. CO 2 assimilation rate was strongly controlled by stomata and was almost the half of that previously reported for temperate environments. In accordance with previous works, K was the most effective osmoticum accumulated in oilseed rape leaves under stressful conditions. As a result, leaf K concentration was correlated negatively with Oil and positively with protein concentration; these two quality traits are inversely affected by stressful conditions. Exclusion of Na by K (higher leaf K/Na ratio) at the reproductive stages was related to lower Oil in oilseed rape, which is a salinity tolerant species. A negative correlation found between leaf K and Ca concentrations can be indicative of a partial substitution of K by Ca, in its osmotic role, in oilseed rape grown on calcareous soils under semi-arid conditions.

Selenium ameliorates salinity stress in Petroselinum crispum by modulation of photosynthesis and by reducing shoot Na accumulation

This study was performed to understand the mechanisms for Se-enhanced resistance of parsley (Petroselinum crispum L.) plants to salinity stress. Plant growth was negatively affected by salt stress; however, Se treatments at 1 mg/L significantly improved the growth rate and enhanced the salt tolerance of seedlings. This increased tolerance in Se-supplied plants was obtained by reduced damaging effect on maximal quantum yield of photosystem II (PSII) (F v/F m) coupled with higher levels of carotenoids and non-photochemical quenching (NPQ). The performance index (PIABS), as evidence for modulation of PSII function, was downregulated by salt stress; while Se mitigated this effect. Moreover, analysis of OJIP transients demon-strated that Se reduced salt damaging effect on PSII function through improvement of excitation energy trapping (TR0/CS) and electron transport (ET0/CS) per excited cross-section of leaf. The Na concentrations in shoots and roots of parsley seedlings considerably enhanced after NaCl treatment. Interestingly, treatment of salt-stressed plants with Se decreased the Na contents in shoots via the limitation of the root-to-shoot translocation of Na and exclusion of Na from cell sap, as well as the retention of K/Na and Ca/Na ratios. These data provide the first evidence that the Se application alleviates salinity stress by enhancing PSII function and by decreasing Na content in the shoot via binding of Na to the root cell wall.

Transcriptome Analysis of the Response to NaCl in Suaeda maritima Provides an Insight into Salt Tolerance Mechanisms in Halophytes.

Although salt tolerance is a feature representative of halophytes, most studies on this topic in plants have been conducted on glycophytes. Transcriptome profiles are also available for only a limited number of halophytes. Hence, the present study was conducted to understand the molecular basis of salt tolerance through the transcriptome profiling of the halophyte Suaeda maritima, which is an emerging plant model for research on salt tolerance. Illumina sequencing revealed 72,588 clustered transcripts, including 27,434 that were annotated using BLASTX. Salt application resulted in the 2-fold or greater upregulation of 647 genes and downregulation of 735 genes. Of these, 391 proteins were homologous to proteins in the COGs (cluster of orthologous groups) database, and the majorities were grouped into the poorly characterized category. Approximately 50% of the genes assigned to MapMan pathways showed homology to S. maritima. The majority of such genes represented transcription factors. Several genes also contributed to cell wall and carbohydrate metabolism, ion relation, redox responses and G protein, phosphoinositide and hormone signaling. Real-time PCR was used to validate the results of the deep sequencing for the most of the genes. This study demonstrates the expression of protein kinase C, the target of diacylglycerol in phosphoinositide signaling, for the first time in plants. This study further reveals that the biochemical and molecular responses occurring at several levels are associated with salt tolerance in S. maritima. At the structural level, adaptations to high salinity levels include the remodeling of cell walls and the modification of membrane lipids. At the cellular level, the accumulation of glycinebetaine and the sequestration and exclusion of Na+ appear to be important. Moreover, this study also shows that the processes related to salt tolerance might be highly complex, as reflected by the salt-induced enhancement of transcription factor expression, including hormone-responsive factors, and that this process might be initially triggered by G protein and phosphoinositide signaling.

Comparative growth and physiological responses of two wheat (Triticum aestivum L.) cultivars differing in salt tolerance to salinity and cyclic drought stress

Two cultivars of wheat (Triticum aestivum L.) with differential salinity tolerance were compared by evaluating the growth attributes, pigment composition and accumulation of Na+, K+, Zn2+, Fe 2+, Mn 2+ and proline. Wheat cultivars Al-Moiaya (AM) (salt tolerant) and Habbe-Druma (HD) (salt sensitive) were subjected to four levels of salinity (1.21 dS m−1, 4.4 dS m−1, 8.8 dS m−1 and 13.2 dS m−1) in factorial combinations with three drought stress (FC 30%, FC 60% and FC 90%) treatments in a randomized complete block design. Plant dry weight, leaf area ratio (LAR), soluble protein and total chlorophyll (Chl) content were higher in AM than HD. Salt-tolerant AM maintains a higher K+/ Na+ ratio and thereby is able to grow better than the salt-sensitive HD under both the stresses. The lower foliar Na+ in AM resulted in retention of higher Chl content, reflected in the strong positive correlations between plant ion status and Chl contents (Na+-Chl r2 = 0.83; Chl- Fe2+ r2 = 0.76; Zn2+ r2 = 0.93 and Mn2+ r2 = 0.88). In conclusion, our results suggested that the K+/Na+ ratio, exclusion of Na+ and ion homeostasis play much more important roles in the tolerance to salinity and drought stress than the compatible osmolyte, proline.

Salt Stress Induced Changes in the Exoproteome of the Halotolerant Bacterium Tistlia consotensis Deciphered by Proteogenomics

The ability of bacteria to adapt to external osmotic changes is fundamental for their survival. Halotolerant microorganisms, such as Tistlia consotensis, have to cope with continuous fluctuations in the salinity of their natural environments which require effective adaptation strategies against salt stress. Changes of extracellular protein profiles from Tistlia consotensis in conditions of low and high salinities were monitored by proteogenomics using a bacterial draft genome. At low salinity, we detected greater amounts of the HpnM protein which is involved in the biosynthesis of hopanoids. This may represent a novel, and previously unreported, strategy by halotolerant microorganisms to prevent the entry of water into the cell under conditions of low salinity. At high salinity, proteins associated with osmosensing, exclusion of Na+ and transport of compatible solutes, such as glycine betaine or proline are abundant. We also found that, probably in response to the high salt concentration, T. consotensis activated the synthesis of flagella and triggered a chemotactic response neither of which were observed at the salt concentration which is optimal for growth. Our study demonstrates that the exoproteome is an appropriate indicator of adaptive response of T. consotensis to changes in salinity because it allowed the identification of key proteins within its osmoadaptive mechanism that had not previously been detected in its cell proteome.

PERFORMANCE OF TOMATO (LYSOPERSICON ESCULENTUM) GERMPLASMS GROWN IN BANGLADESH FOR SALINITY TOLERANCE MPLASM

A solution culture experiment was conducted to screen out a number of Bangladeshi tomato germplasms for salinity tolerance by exposed to control, 8, 12 dS/m NaCl (salt stress). Salinity tolerance of tomato germplasms were evaluated with respect to salinity tolerance index, shoot and root dry matter production, shoot Na + , K + , Ca 2+ accumulation and their respective ratios. A tolerance index was calculated for every single germplasm in root, stem and leaf dry weights and in the K/Na and Ca/Na parameters of these organs. Tomato germplasms responded differently to salt tolerance. Based on the salinity tolerance index caused by the NaCl treatment “BT14 (BARI Tomato 14)” and “BHT5 (BARI Hybrid Tomato 5)” were found to be most tolerant germplasms to salinity with highest salinity tolerance index, root-shoot dry matter production, accumulation of K and Ca and exclusion of Na. Thus, “BT14” and “BHT5” can be regarded as a breeding material for development of new tomato varieties for tolerance to salinity. Key words : Tomato germplasms, salinity, tolerance index, dry matter, Ion concentration