SALT TOLERANCE

Salinity stress negatively impacts agricultural yield throughout the world affecting production whether it is for subsistence or economic gain. The plant response to salinity consists of numerous processes that must function in coordination to alleviate both cellular hyperosmolarity and ion disequilibrium. In addition, crop plants must be capable of satisfactory biomass production in a saline environment (yield stability). Tolerance and yield stability are complex genetic traits that are difficult to establish in crops since salt stress may occur as a catastrophic episode, be imposed continuously or intermittently, or become gradually more severe, and at any stage during development. However, cell biology and molecular genetics research is providing new insight into the plant response to salinity and is identifying genetic determinants that effect salt tolerance. Recent confirmation that many salt tolerance determinants are ubiquitous in plants has led to the use of genetic models, like Arabidopsis thaliana, to further dissect the plant salt stress response. Since many of the most fundamental salt tolerance determinants are those that mediate cellular ion homeostasis, this review will focus primarily on the functional essentiality of ion homeostasis mechanisms in plant salt tolerance. The transport systems that facilitate cellular capacity to utilize Na + for osmotic adjustment and growth and the role of the Salt-Overly-Sensitive (SOS) signal transduction pathway in the regulation of ion homeostasis and salt tolerance will be particularly emphasized. A perspective will be presented that integrates cellular based stress signaling and ion homeostasis mechanisms into a functional paradigm for whole plants and defines biotechnology strategies for enhancing salt tolerance of crops.

Salinity has been an important historical factor which has influenced the life span of agricultural systems. Around 10% of the total cropped land surface is covered with different types of salt-affected soils and the Asian continent accounts for the largest area affected by the salinity of various intensities. Cyanobacteria are capable of not only surviving, but thriving in conditions which are considered to be inhabitable, tolerating desiccation, high temperature, extreme pH and high salinity, illustrating their capacity to acclimatise to extreme environments. Until recently, the responses of cyanobacteria to salinity stresses were poorly documented as compared to heterotrophic bacteria and phototrophic eukaryotic algae. Cyanobacteria can be used to reclaim alkaline soils and fertility can be improved for subsequent cultivation of cereal crops, sugarcane and horticultural crops. Therefore we present here a review on cyanobacterial reclamation of salt-affected soil. Substantial progress has been made towards better understanding of the physiological mechanisms responsible for salinity tolerance and osmotic adjustment in cyanobacteria. Many researchers throughout the world have worked on probable mechanisms of salt tolerance studies in cyanobacteria. These organisms evolved about 3,000 million years ago and are considered to be the primary colonisers of the inhospitable ecosystems. The physiological aspects for the adaptation of cyanobacteria to high salinities include (a) synthesis and accumulation of osmoprotective compounds, (b) maintenance of low internal concentrations of inorganic ions and (c) expression of a set of salt-stress proteins. Exposure of cyanobacterial cells to different abiotic stresses resulted in rapid expression of several stress-regulated proteins and modifications in protein synthesis programme. The synthesis of organic solutes like disaccharides (sucrose, trehalose and glucosyl glycerol), quaternary amines (glycine betaine) and free amino acids (glutamine) are well-documented. The protection against alkaline environment is provided by the synthesis of specific fatty acids, sucrose- and osmotic-stress-induced proteins. In cyanobacteria, accumulation of internal osmoticum in the form of inorganic ions and prevention of intracellular Na+ accumulation by the curtailment of Na influx and by efficient active efflux mechanisms or metabolic adjustments have been investigated in depth. The Na+ extrusion in cyanobacteria is driven by a Na+/H+ antiporter, which is energised by enhanced activity of cytochrome oxidase. The inhibition of sodium ion influx appears to be a major mechanism for the survival of cyanobacteria against salt stress and synthesis of salt-stress proteins have been found in cyanobacteria. These organisms have been recognised as an important agent in the stabilisation of soil surfaces primarily through the production of extracellular polysaccharides which are prominent agents in the process of aggregate formation and increase in soil fertility. Cyanobacterial application results in the enrichment of soil with fixed nitrogen, soil structure improvement and declining trend of pH, electrical conductivity (EC) and Na+. The extracellular polysaccharides excreted by cyanobacteria have been reported to be responsible for binding of soil particles, thus, leading to the formation of a tough and entangled superficial structure that improves the stability of soil surface and protects it from erosion. The potential impact of these organisms on agriculture through their use as soil conditioners, plant growth regulators and soil health ameliorators has been well-recognised. Besides bringing about an improvement in the yield of rice, cyanobacteria produce direct and indirect beneficial changes in the physical, chemical and biological properties of soil and soil–water interface in the rice fields, which are of agronomic importance. Certain cyanobacteria have been found not only to grow in saline ecosystems but also improve the physico-chemical properties of the soil by enriching them with carbon, nitrogen and available phosphorus. Flushing of field may not be effective for the reclamation of saline soils and the addition of cyanobacterium inoculum along with the addition of gypsum is required before irrigation to ameliorate saline soils. Nitrogen-fixing cyanobacteria can be used as biological input to improve soil texture, conserve moisture, scavenge the toxic sodium cation from the soil complex and improve the properties of soils. Virtually negligible information exists on the genetics of cyanobacterial halotolerance. The presence of combined nitrogen which effectively curtails sodium accumulation and supports extra nitrogen demand for osmoregulation during slat stress confers considerable salt tolerance on cyanobacteria.

Effects of hormonal priming with abscisic acid (ABA), salicylic acid (SA), or ascorbic acid on wheat (Triticum aestivum cv. Auqab - 2000) germination and seedling growth under normal (4 dS/ cm) and saline (15 dS/ cm) conditions were studied to determine their usefulness in ...

Salinity limits the production capabilities of agricultural soils in large areas of the world. Both breeding and screening germplasm for salt tolerance encounter the following limitations: (a) different phenotypic responses of plants at different growth stages, (b) different physiological mechanisms, (c) complicated genotype × environment interactions, and (d) variability of the salt-affected field in its chemical and physical soil composition. Plant molecular and physiological traits provide the bases for efficient germplasm screening procedures through traditional breeding, molecular breeding, and transgenic approaches. However, the quantitative nature of salinity stress tolerance and the problems associated with developing appropriate and replicable testing environments make it difficult to distinguish salt-tolerant lines from sensitive lines. In order to develop more efficient screening procedures for germplasm evaluation and improvement of salt tolerance, implementation of a rapid and reliable screening procedure is essential. Field selection for salinity tolerance is a laborious task; therefore, plant breeders are seeking reliable ways to assess the salt tolerance of plant germplasm. Salt tolerance in several plant species may operate at the cellular level, and glycophytes are believed to have special cellular mechanisms for salt tolerance. Ion exclusion, ion sequestration, osmotic adjustment, macromolecule protection, and membrane transport system adaptation to saline environments are important strategies that may confer salt tolerance to plants. Cell and tissue culture techniques have been used to obtain salt tolerant plants employing two in vitro culture approaches. The first approach is selection of mutant cell lines from cultured cells and plant regeneration from such cells (somaclones). In vitro screening of plant germplasm for salt tolerance is the second approach, and a successful employment of this method in durum wheat is presented here. Doubled haploid lines derived from pollen culture of F1 hybrids of salt-tolerant parents are promising tools to further improve salt tolerance of plant cultivars. Enhancement of resistance against both hyper-osmotic stress and ion toxicity may also be achieved via molecular breeding of salt-tolerant plants using either molecular markers or genetic engineering.

Salinity is a major abiotic stress affecting approximately 7% of the world's total land area resulting in billion dollar losses in crop production around the globe. Recent progress in molecular genetics and plant electrophysiology suggests that the ability of a plant to maintain a high cytosolic K 1 /Na 1 ratio appears to be critical to plant salt tolerance. So far, the major efforts of plant breeders have been aimed at improving this ratio by minimizing Na 1 uptake and transport to shoot. In this paper, we discuss an alternative approach, reviewing the molecular and ionic mechanisms contributing to potassium homeostasis in salinized plant tissues and discussing prospects for breeding for salt tolerance by targeting this trait. Major K 1 transporters and their functional expression under saline conditions are reviewed and the multiple modes of their control are evaluated, including ameliorative effects of compatible solutes, polyamines and supplemental calcium. Subsequently, the genetic aspects of inheritance of K 1 transport 'markers' are discussed in the general context of salt tolerance as a polygenic trait. The molecular identity of 'salt tolerance' genes is analysed, and prospects for future research and breeding are examined.

Effects of hormonal priming with abscisic acid (ABA), salicylic acid (SA), or ascorbic acid on wheat (Triticum aestivum cv. Auqab - 2000) germination and seedling growth under normal (4 dS/ cm) and saline (15 dS/ cm) conditions were studied to determine their usefulness in ...

The degree of salt tolerance of two newly developed genotypes of spring wheat, S24 and S36 was assessed with respect to their parents, LU26S (from Pakistan) and Kharchia (from India). These four lines along with a salt-tolerant genotype SARC-1 and two salt-sensitive cvs Potohar and Yecora Rojo were subjected to salinized sand culture containing 0, 125 or 250 mol m−3 NaCl in full strength Hoagland's nutrient solution.S24 produced significantly greater grain yield and had greater 1000 seed weight and number of tillers per plant than those of the other cultivars /lines. S36 was not significantly different from its parents in seed yield and yield components. SARC-1 was the second highest in grain yield of all cultivars/lines, but it did not differ significantly from LU26S and Kharchia in 1000 seed weight and number of tillers per plant.The greater degree of salt tolerance of S24 could be related to its lower accumulation of Na+ in the leaves and maintenance of higher leaf K/Na ratios and K versus Na selectivity as compared to its parents. S36, which was as good as its parents in growth, also had lower Na+ and higher K/Na ratios and K versus Na selectivity in the leaves at the highest salt level than those in its parents. SARC-1 did not differ from LU26S and Kharchia in ionic content or K/Na ratios and K versus Na selectivities of both leaves and roots. Both the salt-sensitive cultivars, Potohar and Yecora Rojo, had significantly greater leaf Na+ and Cl− concentrations and lower leaf K/Na ratios and K versus Na selectivities than all the salt-tolerant lines examined in this study.From this study it is evident that improvement in salt tolerance of spring wheat is possible through selection and breeding, and pattern of ion accumulation is not consistent among the salt-tolerant genotypes in relation to their degree of salt tolerance.

Extreme environments have for long been considered to be populated almost exclusively by prokaryotic organisms and therefore monopolized by bacteriologists. Solar salterns are natural hypersaline environments characterized by extreme concentrations of NaCl, often high concentrations of other ions, high uv irradiation and in some cases extremes in pH. In 2000 fungi were first reported to be active inhabitants of solar salterns. Since then many new species and species previously known only as food contaminants have been discovered in hypersaline environments around the globe. The eukaryotic microorganism most studied for its salt tolerance is Saccharomyces cerevisiae. However, S. cerevisiae is rather salt sensitive and not able to adapt to hypersaline conditions. In contrast, some species like Debaryomyces hansenii, Hortaea werneckii, and Wallemia ichthyophaga have been isolated globally from natural hypersaline environments. We believe that all three are more suitable model organisms...

Salinity is one of the major abiotic stresses that reduce plant growth and crop productivity in many vegetable production areas of the world. Grafting can represent an interesting tool to avoid or reduce yield losses caused by salinity stress in high-yielding genotypes belonging to Solanaceae and Cucurbitaceae families. Grafting is an integrative reciprocal process and, therefore, both scion and rootstock can influence salt tolerance of grafted plants. Grafted plants grown under saline conditions often exhibited better growth and yield, higher photosynthesis and leaf water content, greater root-to-shoot ratio, higher accumulation of compatible osmolytes, abscisic acid and polyamines in leaves, greater antioxidant capacity in leaves, and lower accumulation of Na + and/or Cl − in shoots than ungrafted or self-grafted plants. This report gives an overview of the recent literature on the salinity response of grafted plants and the mechanisms of salt tolerance in grafted plants related to the morphological root characteristics and the physiological and biochemical processes. The review will conclude by identifying several prospects for future researches aiming to improve the role of grafting in vegetable crops grown under saline conditions.

Recent trends and future demographic projections suggest that the need to produce more food and fibre will necessitate effective utilization of salt-affected land and saline water resources. Currently at least 20 per cent of the world's irrigated land is salt affected and/or irrigated with waters containing elevated levels of salts. Several major irrigation schemes have suffered from the problems of salinity and sodicity, reducing their agricultural productivity and sustainability. Productivity enhancement of salt-affected land and saline water resources through crop-based management has the potential to transform them from environmental burdens into economic opportunities. Research efforts have led to the identification of a number of field crops, forage grasses and shrubs, aromatic and medicinal species, bio-fuel crops, and fruit tree and agroforestry systems, which are profitable and suit a variety of salt-affected environments. Several of these species have agricultural significance in terms of their local utilization on the farm. Therefore, crop diversification systems based on salt-tolerant plant species are likely to be the key to future agricultural and economic growth in regions where salt-affected soils exist, saline drainage waters are generated, and/or saline aquifers are pumped for irrigation. However, such systems will need to consider three issues: improving the productivity per unit of salt-affected land and saline water resources, protecting the environment and involving farmers in the most suitable and sustainable crop diversifying systems to mitigate any perceived risks. This review covers different aspects of salt-affected land and saline water resources, synthesizes research knowledge on salinity/sodicity tolerances in different plant species, and highlights promising examples of crop diversification and management to improve and maximize benefits from these resources.

The effects of NaCl stress on the activity of antioxidant enzyme such as superoxide dismutase (SOD: EC 1.15.1.1), peroxidase (POD: EC 1.11.1.7), glutathione reductase (GR: EC 1.6.4.2), rate of lipid peroxidation, gas-exchange, chlorophyll content and chlorophyll fluorescence were investigated in two cotton cultivars, Guazuncho and Pora (hybrids between Gossypium hirsutum )/G. arboretum )/G. raimondii ) grown in nutrient solution. Plants were treated with three salt concentrations (50, 100 and 200 mol m (3 NaCl) for 21 days. The SOD activity in Pora increases with the increase in the intensity of NaCl stress, but salt treatment had no significant effect on this enzyme activity in Guazuncho. The POD and GR activities showed similar trends under salt stress, in both cotton cultivars. In Pora, there was an average increase in GR activity of about 53%, but there was no further increase at higher NaCl concentrations. In Guazuncho, no change in GR activity was observed. Net photosynthesis and stomatal conductance decreased in response to salt stress, but Pora showed a smaller reduction in photosynthesis than Guazuncho. The results indicated that stomatal aperture limited leaf photosynthetic capacity in the NaCl-treated plants of both cultivars. However, significant reduction in the leaf chlorophyll contents due to NaCl stress was observed only on Guazuncho. In both cotton cultivars, the photochemical efficiency of PSII was not affected by salt stress. These results suggest that salttolerant cotton varieties may have a better protection against reactive oxygen species (ROS) by increasing the activity of antioxidant enzymes under salt stress. #

A pot study was conducted to determine the effects of arbuscular mycorrhizal (AM) fungi (Glomus mosseae and Paraglomus occultum) and salt (NaCl) stress on growth, photosynthesis, root morphology and ionic balance of citrus (Citrus tangerine Hort. ex Tanaka) seedlings. Eighty-five-day-old seedlings were exposed to 100 mM NaCl for 60 days to induce salt stress. Mycorrhizal colonization of citrus seedlings was not affected by salinity when associated with P. occultum, but significantly decreased when with G. mosseae. Compared with the nonmycorrhizal controls, mycorrhizal seedlings generally had greater plant height, stem diameter, shoot, root and total plant biomass, photosynthetic rate, transpiration rate and stomatal conductance under the 0 and 100 mM NaCl stresses. Root length, root projected area and root surface area were also higher in the mycorrhizal than in the nonmycorrhizal seedlings, but higher root volume in seedlings with G. mosseae. Leaf Na ? concentrations were significantly decreased, but leaf K ? and Mg 2? concentrations and the K ? /Na ? ratio were increased when seedlings with both G. mosseae and P. occultum. Under the salt stress, Na ? concentrations were increased but K ? concentrations decreased in the mycorrhizal seedlings. Under the salt stress, Ca 2? concentrations were increased in the seedlings with P. occultum or without AM fungi (AMF), but decreased with G. mosseae. Ratios of both Ca 2? /Na ? and Mg 2? /Na ? were also increased in seedlings with G. mosseae under the non-salinity stress, while only the Mg 2? / Na ? ratio was increased in seedlings with P. occultum under the salt stress. Our results suggested that salt tolerance of citrus seedlings could be enhanced by associated AMF with better plant growth, root morphology, photosynthesis and ionic balance.

Growth and water uptake both decreases when tomato plants are irrigated with saline water. To determine the relative contribution of physiological traits to these decreases plant fresh and dry weight, leaf area, leaf water (c w ) and osmotic (c P ) potentials, gas exchange parameters, stomatal density, leaf chlorophyll and Na content were investigated in the tomato (Lycopersicon esculentum) cultivars, Daniela and Moneymaker. Plants were grown in greenhouse, in sand culture, and irrigated with a complete nutrient solution supplied with 0 (control), 35 and 70 mM NaCl over a period of 2 months. Salinity reduced plant dry weight, height and number of leaves even at 35 mM NaCl. Leaf c w and c P decreased with salinity but leaf turgor pressures were significantly higher in salinised than in control plants which suggests that bulk tissue turgor did not limit growth under the saline conditions tested. Increasing salinity in the irrigation solution led to both morphological changes [(reduction of plant leaf area and stomatal density) and physiological changes [reduction of stomatal conductance, transpiration, and net CO 2 assimilation (A CO 2 )] Plant water uptake, measured as the difference between volume of nutrient solution supplied and drainage collected, was closely related to transpiration, stomatal conductance, and stomatal density. Chlorophyll content per unit of leaf area increased with salinity. Reduction of net A CO 2 with salinity was explained in higher degree by stomatal conductance and stomatal density than by Na accumulation in the leaves. Although plant water uptake was similar for the two cultivars, Daniela transported, per unit of water uptake, more Na to the leaves than did Moneymaker. However, Daniela reduced leaf area less than did Moneymaker. Water use efficiency, calculated either as the ratio between total plant dry matter and total plant water uptake, or as the ratio between net A CO 2 and transpiration, did not change under our saline growth conditions. The contribution of the observed salt-responses to reduction in shoot water loss, plant water uptake and salt loading, while keeping water use efficiency, is discussed in relation to salt tolerance. Because some of these salt-responses take a long time to develop, growing seedlings in seedbeds with saline media could be of interest to better tolerate further salty conditions in the field or greenhouse.

BACKGROUND: The traditional use of sodium chloride (NaCl) fulfills various important rheological, technological and sensory properties in the manufacturing of yeast-leavened products. However, the use of NaCl in food production has been discussed controversially since a high intake of sodium seems to be associated with hypertension. This study investigates the baking quality parameters of wheat breads containing various levels of NaCl (0-40 g NaCl kg −1 flour).

Crop salt tolerance is generally assessed as the relative yield response to increasing root zone salinity, expressed as soil (EC e ) or irrigation water (EC w ) electrical conductivity. Alternatively, the dynamic process of salt accumulation into the shoot relative to the shoot biomass has also been considered as a tolerance index. These relationships are graphically represented by two intersecting linear regions, which identify (1) a specific threshold tolerance, at which yield begins to decrease, and (2) a declining region, which defines the yield reduction rate. Although the salinity threshold is intuitively a critical parameter for establishing plant salt tolerance, we focused our interest on physiological modifications that may occur in the plant at salinity higher than the so-called tolerance threshold. For this purpose, we exposed hydroponically grown tomato plants to eight different salinity levels (EC = 2.5 (non-salinized control); 4.2; 6.0; 7.8; 9.6; 11.4; 13.2; 15.0 dS m −1 ). Based on biomass production, water relations, leaf ions accumulation, leaf and root abscisic acid and stomatal conductance measurements, we were able to identify a specific EC value (approximately 9.6 dS m −1 ) at which a sharp increase of the shoot and root ABA levels coincided with (1) a decreased sensitivity of stomatal response to ABA; (2) a different partitioning of Na + ions between young and mature leaves; (3) a remarkable increase of the root-to-shoot ratio. The specificity and functional significance of this response in salt stress adaptation is discussed.

Two components of salinity stress are a reduction in water availability to plants and the formation of reactive oxygen species. In this work, we have used quinoa (Chenopodium quinoa), a dicotyledonous C3 halophyte species displaying optimal growth at approximately 150 mM NaCl, to study mechanisms by which halophytes cope with the afore-mentioned components of salt stress. The relative contribution of organic and inorganic osmolytes in leaves of different physiological ages (e.g. positions on the stem) was quantified and linked with the osmoprotective function of organic osmolytes. We show that the extent of the oxidative stress (UV-B irradiation) damage to photosynthetic machinery in young leaves is much less when compared with old leaves, and attribute this difference to the difference in the size of the organic osmolyte pool (1.5-fold difference under control conditions; sixfold difference in plants grown at 400 mM NaCl). Consistent with this, salt-grown plants showed higher Fv/Fm values compared with control plants after UV-B exposure. Exogenous application of physiologically relevant concentrations of glycine betaine substantially mitigated oxidative stress damage to PSII, in a dosedependent manner. We also show that salt-grown plants showed a significant (approximately 30%) reduction in stomatal density observed in all leaves. It is concluded that accumulation of organic osmolytes plays a dual role providing, in addition to osmotic adjustment, protection of photosynthetic machinery against oxidative stress in developing leaves. It is also suggested that salinityinduced reduction in stomatal density represents a fundamental mechanism by which plants optimize water use efficiency under saline conditions.

Significant progress has been made in unraveling the molecular biology of rice in the past two decades. Today, rice stands as a forerunner amongst the cereals in terms of details known on its genetics. Evidence show that salt tolerance in plants is a quantitative trait. Several traditional cultivars, landraces, and wild types of rice like Pokkali, CSR types, and Porteresia coarctata appear as promising materials for donation of requisite salt tolerance genes. A large number of quantitative trait loci (QTL) have been identified for salt tolerance in rice through generation of recombinant inbred lines and are being mapped using different types of DNA markers. Salt-tolerant transgenic rice plants have been produced using a host of different genes and transcript profiling by micro-and macroarraybased methods has opened the gates for the discovery of novel salt stress mechanisms in rice, and comparative genomics is turning out to be a critical input in this respect. In this paper, we present a comprehensive review of the genetic, molecular biology, and comparative genomics effort towards the generation of salt-tolerant rice. From the data on comprehensive transcript expression profiling of clones representing salt-stress-associated genes of rice, it is shown that transcriptional and translational machineries are important determinants in controlling salt stress response, and gene expression response in tolerant and susceptible rice plants differs mainly in quantitative terms.

Twenty rhizobacterial strains containing 1-aminocyclopropane-1-carboxylate deaminase were isolated from the rhizosphere of salt-affected maize fields. They were screened for their growth-promoting activities under axenic conditions at 1, 4, 8, and 12 dSÁm -1 salinity levels. Based upon the data of the axenic study, the 6 most effective strains were selected to conduct pot trials in the wire house. Besides one original salinity level (1.6 dSÁm -1 ), 3 other salinity levels (4, 8, and 12 dSÁm -1 ) were maintained in pots and maize seeds inoculated with selected strains of plant growth-promoting rhizobacteria, as well as uninoculated controls were sown. Results showed that the increase in salinity level decreased the growth of maize seedlings. However, inoculation with rhizobacterial strains reduced this depression effect and improved the growth and yield at all the salinity levels tested. Selected strains significantly increased plant height, root length, total biomass, cob mass, and grain yield up to 82%, 93%, 51%, 40%, and 50%, respectively, over respective uninoculated controls at the electrical conductivity of 12 dSÁm -1 . Among various plant growth-promoting rhizobacterial strains, S5 (Pseudomonas syringae), S14 (Enterobacter aerogenes), and S20 (Pseudomonas fluorescens) were the most effective strains for promoting the growth and yield of maize, even at high salt stress. The relatively better salt tolerance of inoculated plants was associated with a high K + /Na + ratio as well as high relative water and chlorophyll and low proline contents.

Background: Field pea (Pisum sativum L.) is a self-pollinating, diploid, cool-season food legume. Crop production is constrained by multiple biotic and abiotic stress factors, including salinity, that cause reduced growth and yield. Recent advances in genomics have permitted the development of low-cost high-throughput genotyping systems, allowing the construction of saturated genetic linkage maps for identification of quantitative trait loci (QTLs) associated with traits of interest. Genetic markers in close linkage with the relevant genomic regions may then be implemented in varietal improvement programs. Results: In this study, single nucleotide polymorphism (SNP) markers associated with expressed sequence tags (ESTs) were developed and used to generate comprehensive linkage maps for field pea. From a set of 36,188 variant nucleotide positions detected through in silico analysis, 768 were selected for genotyping of a recombinant inbred line (RIL) population. A total of 705 SNPs (91.7%) successfully detected segregating polymorphisms. In addition to SNPs, genomic and EST-derived simple sequence repeats (SSRs) were assigned to the genetic map in order to obtain an evenly distributed genome-wide coverage. Sequences associated with the mapped molecular markers were used for comparative genomic analysis with other legume species. Higher levels of conserved synteny were observed with the genomes of Medicago truncatula Gaertn. and chickpea (Cicer arietinum L.) than with soybean (Glycine max [L.] Merr.), Lotus japonicus L. and pigeon pea (Cajanus cajan [L.] Millsp.). Parents and RIL progeny were screened at the seedling growth stage for responses to salinity stress, imposed by addition of NaCl in the watering solution at a concentration of 18 dS m -1. Salinity-induced symptoms showed normal distribution, and the severity of the symptoms increased over time. QTLs for salinity tolerance were identified on linkage groups Ps III and VII, with flanking SNP markers suitable for selection of resistant cultivars. Comparison of sequences underpinning these SNP markers to the M. truncatula genome defined genomic regions containing candidate genes associated with saline stress tolerance.

Fresh groundwater resources in Egypt contribute to some 20% of the total potential of water resources in Egypt. The Ministry of Water Resources and Irrigation (MWRI) increasingly recognizes its importance in the overall water resources management. The need for a more comprehensive groundwater management approach has led to the establishment of the Groundwater Sector (GWS) in December 1999. The GWS is now the sole responsible governmental agency for management of all groundwater resources and related water resources. The mandate of the GWS is: formulating and implementing the general policy for developing and managing groundwater and related water resources (flash floods, rainwater harvesting and desalinated water) on the national, regional and sub-regional level. Desalination of brackish groundwater in Egypt has a great potential with respect to the availability of the resource. All major aquifer systems in Egypt contain vast quantities of brackish groundwater. The exploitation of this resource is still limited. With the current low price of brackish water desalination there is a growing interest towards its exploitation. Brackish water desalination plants in Egypt confirm the potential of this solution. Other uses for brackish groundwater that are being considered are agriculture (salt tolerant crops) and fisheries (shrimp farms). The elements of the vision for desalination of brackish groundwater are: environmental sustainability through recycling of water and re-infiltration; public-private partnerships for exploitation, especially in the tourism sector; private sector financing through accepted modalities (BOT, DBO, etc.). With the input of experience from the Netherlands through the GWS project a new program for desalination was started. This program aims to provide the necessary concepts and data on desalination of brackish groundwater in Egypt to allow the GWS to formulate a clear policy in this regard.

There are a range of plants that are capable of growing under conditions of saline soil and water. Many of these plants represent a feed resource for livestock. At the lower levels of salinity (<15 dS m À1 ) both legumes and grasses with moderate salt tolerance are capable of providing 5-10 t of edible dry matter (DM) year À1 , particularly when the availability of water is high. At high salt concentrations (>25 dS m À1 ), production levels drop and the plant options decrease significantly. However, even at these high salinities there are a range of halophytic grasses and shrubs that will produce between 0.5 and 5 t of edible DM year À1 . The crude protein and digestible fibre content of these plants is variable but is probably not directly influenced by the salinity level. Importantly though, the mineral composition of the plants may be significantly altered by the concentration and type of salts in the soil and water. For plants with moderate salt tolerance, accumulation of sulfur and selenium has been reported. For the halophytic plants, particularly the chenopod shrubs, sodium, potassium, chloride, calcium and magnesium may all accumulate to be above the maximum tolerable levels for livestock. The high concentrations of sodium chloride in particular will cause depressed feed intake and under some conditions will compromise animal health. It is also not unusual to find that plants growing in saline environments accumulate a range of secondary compounds. These may have beneficial effects on grazing livestock (e.g., vitamin E and betaine) or be may be toxic (e.g., oxalate, coumarin and nitrate). Importantly, these plants can be managed so as to provide a significant contribution to a feeding system for ruminants. Prospects for the future are good, as to date, there has been little effort to improve the feeding value of salt tolerant plants through breeding or selection, or to select livestock that are more capable of tolerating high salt intakes. Crown

A pot experiment was carried out under glasshouse conditions with melon (Cucumis melo) cv. "Tempo F1" in a mixture of peat, perlite and sand (1:1:1) to investigate the effects of external proline and potassium nitrate applications to salinity-treated (150 mM) plants with respect to fruit yield, plant growth, some physiological parameters and ion uptake. Treatments were-(i) control (C): plants receiving nutrient solution, (ii) salinity treatment, as for control plus 150 mM NaCl. Salinity treatment was combined with or without either 5 mM supplementary KNO 3 or 10 mM proline. The salt treatment (150 mM NaCl) led to significant decreases in plant growth, fruit yield, relative water content (RWC), stomatal density, uptake of Ca 2+ , K + and N, and chlorophyll a and b contents, accompanied by significant increases in Na + uptake, proline concentration and membrane permeability. Supplementary KNO 3 and proline treatments significantly ameliorated the adverse effects of salinity on plant growth, fruit yield and the physiological parameters examined. This could be attributed to the effects of all the external supplements in maintaining membrane permeability, and increasing concentrations of Ca 2+ , N and K + in the leaves of plants subjected to salt stress.

To study the response of tomato (Solanum lycopersicum cv. Rio Grande) to salinity, the effect on plant growth, water relations, stomatal conductance and Chlorophyll fluorescence was investigated. Tomato plants were grown in peat culture under controlled conditions ...

Salicylic acid (SA) is known to affect photosynthesis under normal conditions and induces tolerance in plants to biotic and abiotic stresses through influencing physiological processes. In this study, physiological processes were compared in salt-tolerant (Pusa Vishal) and salt-sensitive (T44) cultivars of mungbean and examined how much these processes were induced by SA treatment to alleviate decrease in photosynthesis under salt stress. Cultivar T44 accumulated higher leaf Na + and Cl − content and exhibited greater oxidative stress than Pusa Vishal. Activity of antioxidant enzymes, ascorbate peroxidase (APX) and glutathione reductase (GR) was greater in Pusa Vishal than T44. Contrarily, activity of superoxide dismutase (SOD) was greater in T44. The greater accumulation of leaf nitrogen and sulfur through higher activity of their assimilating enzymes, nitrate reductase (NR) and ATP-sulfurylase (ATPS) increased reduced glutathione (GSH) content more conspicuously in Pusa Vishal than T44. Application of 0.5 mM SA increased nitrogen and sulfur assimilation, GSH content and activity of APX and GR. This resulted in the increase in photosynthesis under non-saline condition and alleviated the decrease in photosynthesis under salt stress. It also helped in restricting Na + and Cl − content in leaf, and maintaining higher efficiency of PSII, photosynthetic N-use efficiency (NUE) and water relations in Pusa Vishal. However, application of 1.0 mM SA resulted in inhibitory effects. The effect of SA was more pronounced in Pusa Vishal than T44. These results indicate that SA application alleviates the salt-induced decrease in photosynthesis mainly through inducing the activity of NR and ATPS, and increasing antioxidant metabolism to a greater extent in Pusa Vishal than T44.

Salinity is one of the major abiotic stresses that limits agricultural productivity worldwide. Plant roots function as the primary site of salinity perception. Salt responses in roots are essential for maintaining root functionality, as well as for transmitting the salt signal to shoot for proper salt response and adaptation in the entire plant. Therefore, a thorough understanding of signaling and metabolic mechanisms of salt response in roots is critical for improving plant salt tolerance. Current proteomic studies have provided salt-responsive expression patterns of 905 proteins in 14 plant species. Through integrative analysis of salt-responsive proteins and previous physiological and molecular findings, this review summarizes current understanding of salt responses in roots and highlights proteomic findings on the molecular mechanisms in the fine-tuned salt-responsive networks. At the proteome level, the following processes become dominant in root salt response: (i) salt signal perception and transduction; (ii) detoxification of reactive oxygen species (ROS); (iii) salt uptake/exclusion and compartmentalization; (iv) protein translation and/or turnover dynamics; (v) cytoskeleton/cell wall dynamics; (vi) carbohydrate and energy metabolism; and (vii) other salt-responsive metabolisms. These processes work together to gain cellular homeostasis in roots and determine the overall phenotype of plant growth and development under salt stress.

Yarrowia lipolytica is a fungus that degrades hydrophobic substrates very efficiently. The fungus displays several important characteristics that have encouraged researchers to study various basic biological and biotechnological applications in detail. Although the organism has been used as model system for studying dimorphism, salt tolerance, heterologous protein expression, and lipid accumulation, there are no recent reviews on the environmental and industrial applications of this organism. Included here are applications in bioremediation of environments contaminated with aliphatic and aromatic compounds, organic pollutants, 2,4,6-trinitrotoluene, and metals. A variety of industrially important recent processes for the synthesis of β-hydroxy butyrate, L-dopa, and emulsifiers have also been reviewed. Production of unique inherent enzymes (inulinases, α-mannosidases), novel applications of esterases and lipases, and the use of the fungus for heterologous expression of biotechnologically relevant products have also been highlighted. The review while entailing a general overview focuses critically on some of the recent advances on the applications of this yeast. The examples cited here demonstrate the use of wild-type, mutant as well as genetically manipulated strains of Y. lipolytica for the development of different products, processes, and technologies. This also throws light on how a single organism can be versatile with respect to its metabolic abilities and how it can be exploited for a variety of purposes. This review will thus form a base for future developments in this field.

† Background Mangroves are a group of highly salt-tolerant woody plants. The high water use efficiency of mangroves under saline conditions suggests that regulation of water transport is a crucial component of their salinity tolerance. † Scope This review focuses on the processes that contribute to the ability of mangroves to maintain water uptake and limit water loss to the soil and the atmosphere under saline conditions, from micro to macro scales. These processes include: (1) efficient filtering of the incoming water to exclude salt; (2) maintenance of internal osmotic potentials lower than that of the rhizosphere; (3) water-saving properties; and (4) efficient exploitation of less-saline water sources when these become available. † Conclusions Mangroves are inherently plastic and can change their structure at the root, leaf and stand levels in response to salinity in order to exclude salt from the xylem stream, maintain leaf hydraulic conductance, avoid cavitation and regulate water loss (e.g. suberization of roots and alterations of leaf size, succulence and angle, hydraulic anatomy and biomass partitioning). However, much is still unknown about the regulation of water uptake in mangroves, such as how they sense and respond to heterogeneity in root zone salinity, the extent to which they utilize non-stomatally derived CO 2 as a water-saving measure and whether they can exploit atmospheric water sources.

The physiological and molecular mechanisms of tolerance to osmotic and ionic components of salinity stress are reviewed at the cellular, organ, and whole-plant level. Plant growth responds to salinity in two phases: a rapid, osmotic phase that inhibits growth of young leaves, and a slower, ionic phase that accelerates senescence of mature leaves. Plant adaptations to salinity are of three distinct types: osmotic stress tolerance, Na + or Cl − exclusion, and the tolerance of tissue to accumulated Na + or Cl − . Our understanding of the role of the HKT gene family in Na + exclusion from leaves is increasing, as is the understanding of the molecular bases for many other transport processes at the cellular level. However, we have a limited molecular understanding of the overall control of Na + accumulation and of osmotic stress tolerance at the whole-plant level. Molecular genetics and functional genomics provide a new opportunity to synthesize molecular and physiological knowledge to improve the salinity tolerance of plants relevant to food production and environmental sustainability. 651 Annu. Rev. Plant Biol. 2008.59:651-681. Downloaded from arjournals.annualreviews.org by CSIRO on 06/21/08. For personal use only.

Soil salinity is a major abiotic stress in plant agriculture strongly, influencing plant productivity world-wide. Classical breeding for salt tolerance in crop plants has been attempted to improve field performance without success. Therefore, an alternative strategy is to generate salt tolerant plants through genetic engineering. Several species and experimental approaches have been used in order to identify those genes that are important for salt tolerance. Due to high level of salt tolerance, halophytes are good candidates to identify salt tolerance genes. However, other species such as yeast and glycophytes have also been employed. Three approaches are commonly used to identify genes important for salt tolerance. The first approach is to identify genes involved in processes known to be critical for salt tolerance (osmolyte synthesis, ion homeostasis, etc.). The second approach is to identify genes whose expression is regulated by salt stress. This is relatively simply and applicable to any plant species. Genetic amenability of some species allows the third approach, which consists in the identification of salt tolerance determinants based on functionality. At the moment, there is a large number of reports in the literature claiming that plants with increased salt tolerance have been obtained. The main problem is that different plant species, stage of development, organs, promoters and salt conditions used it is difficult to compare the degree of salt tolerance conferred by different genes. In this review, we discuss progress made towards understanding the molecular elements involved in salt stress responses that have been used in transgenic approaches to improve salt tolerance.

The interactions between salinity, growth and evapotranspiration (Et) were investigated for Typha domingensis Pers. in a greenhouse growth experiment and in Cienega de Santa Clara, a coastal desert marsh in the Colorado River delta in Mexico. Although Typha is often found in brackish as well as fresh water marshes, salinity imposed severe constraints to its growth and distribution. In the 68 day greenhouse experiment, growth was maximal at 1.1 ppt. (control solution), half-maximal at 3.5 ppt. and negligible above 6 ppt.; 75% mortality occurred at 15 ppt. Et decreased with salinity in proportion to growth reduction. In the Cienega, T. domingensis was only found in water of 5-8 ppt. or less. When inflow water was 1.0 ppt., Typha E t was estimated to be 1.3 times pan evaporation (Eo), whereas when inflow water was 3.2 ppt., estimated Et/Eo was only 0.7. An estimated half of the inflow water to the Cienega exited the vegetated portion of the Cienega unused, owing to the salt tolerance limit of Typha. A practical objective of the study was to predict the effect of brine placement from the Yuma Desalting Plant into the Cienega; it was concluded that the resulting inflow salinity of 7-10 ppt. would result in deterioration of the Typha stands owing to excess salinity.

Elsevier Science B.V. All rights reserved PII S 0 3 0 4 -3 7 7 0 ( 9 8 ) 0 0 0 7 3 -4 and saline treatments and higher sulfide concentration in saline treatments. Our results suggest that disturbance is an important component of vegetation change in response to rising sea level, catalyzing rapid shifts in vegetation structure or accelerating wetland loss. # 1998 Elsevier Science B.V. All rights reserved

This review describes physiological mechanisms and selectable indicators of gene action, with the aim of promoting new screening methods to identify genetic variation for increasing the salt tolerance of cereal crops. Physiological mechanisms that underlie traits for salt tolerance could be used to identify new genetic sources of salt tolerance. Important mechanisms of tolerance involve Na 1 exclusion from the transpiration stream, sequestration of Na 1 and Cl 2 in the vacuoles of root and leaf cells, and other processes that promote fast growth despite the osmotic stress of the salt outside the roots. Screening methods for these traits are discussed in relation to their use in breeding, particularly with respect to wheat. Precise phenotyping is the key to finding and introducing new genes for salt tolerance into crop plants.

Increasing salinity tolerance and water-use efficiency in crop plants are two major challenges that agriculture must face in the next decades. Many physiological mechanisms and molecular components mediating crop response to environmental stresses have been identified. However, the functional inter-links between stress adaptation responses have not been completely understood. Using two basil cultivars (Napoletano and Genovese) with contrasting ability to respond to salt stress, here we demonstrate that reduced stomatal density, high ascorbate level and polyphenol oxidase (PPO) activity coordinately contribute to improve basil adaptation and water use efficiency (WUE) in saline environment. The constitutively reduced stomatal density was associated with a "delayed" accumulation of stress molecules (and growth inhibiting signals) such as abscisic acid (ABA) and proline, in the more tolerant Genovese. Leaf volatile profiling also revealed cultivar-specific patterns, which may suggest a role for the volatile phenylpropanoid eugenol and monoterpenes in conferring stress tolerance via antioxidant and signalling functions.

Increased salinity is a stringent problem to crop production while seed pretreatment can effectively induce salt tolerance in plants. Hydrogen peroxide (H 2 O 2 ), a stress signal molecule, was evaluated as seed treatment to produce the metabolic changes, which could lead to improved salt tolerance in wheat. Soaking in 1, 40, 80 and 120 mM H 2 O 2 revealed a low penetration, reaching maximum at 5 h (2.5870.23 mmol g À1 fresh seeds at 120 mM) and declining thereafter to the level of water control by 8 h. This revealed the activation of antioxidants and H 2 O 2 scavenging in seed after 5 h. Seeds treated with 1-120 mM H 2 O 2 for 8 h and germinated in saline (150 mM NaCl) medium curtailed the mean germination time (MGT) being even less than water controls. Level of H 2 O 2 in seedlings arising from H 2 O 2 -treated seeds grown under salinity was markedly lower than salinized controls, suggesting the operation of antioxidant system in them. These seedlings exhibited better photosynthetic capacity, particularly the stomatal conductance (gs), thus improving the leaf gas exchange due to stomatal component of photosynthesis. Moreover, H 2 O 2 treatment improved leaf water relations and maintained turgor. Although Na + and Cl À content increased due to salinity, H 2 O 2 -treated seedlings displayed greater tissue K + , Ca 2+ , NO 3 À PO 4 3À levels and improved K + :Na + ratio. H 2 O 2 treatment enhanced the membrane properties, as revealed from greatly reduced relative membrane permeability (RMP) and less altered ion leakage pattern (comparable to water controls). Seedlings exhibited the expression of two heatstable (stress) proteins with apparent molecular masses of 32 and 52 kDa. Results suggest that H 2 O 2 signals the activation of antioxidants in seed, which persists in the ARTICLE IN PRESS www.elsevier.de/jplph 0176-1617/$ -see front matter (A. Wahid).

Halophytes are defined as plants that are adapted to live in soils containing high concentrations of salt and benefiting from it, and thus represent an ideal model to understand complex physiological and genetic mechanisms of salinity stress tolerance. It is also known that oxidative stress signalling and reactive oxygen species (ROS) detoxification are both essential components of salinity stress tolerance mechanisms. This paper comprehensively reviews the differences in ROS homeostasis between halophytes and glycophytes in an attempt to answer the questions of whether stress-induced ROS production is similar between halophytes and glycophytes; is the superior salinity tolerance in halophytes attributed to higher antioxidant activity; and is there something special about the specific 'pool' of enzymatic and non-enzymatic antioxidants in halophytes. We argue that truly salt-tolerant species possessing efficient mechanisms for Na + exclusion from the cytosol may not require a high level of antioxidant activity, as they simply do not allow excessive ROS production in the first instance. We also suggest that H 2 O 2 'signatures' may operate in plant signalling networks, in addition to well-known cytosolic calcium 'signatures'. According to the suggested concept, the intrinsically higher superoxide dismutase (SOD) levels in halophytes are required for rapid induction of the H 2 O 2 'signature', and to trigger a cascade of adaptive responses (both genetic and physiological), while the role of other enzymatic antioxidants may be in decreasing the basal levels of H 2 O 2 , once the signalling has been processed. Finally, we emphasize the importance of non-enzymatic antioxidants as the only effective means to prevent detrimental effects of hydroxyl radicals on cellular structures.

Salinity does not only stress plants but also challenges human life and the economy by posing severe constraints upon agriculture. To understand salt adaptation strategies of plants, it is central to extend agricultural production to salt-affected soils. Despite high impact and intensive research, it has been difficult to dissect the plant responses to salt stress and to define the decisive key factors for the outcome of salinity signalling. To connect the rapidly accumulating data from different systems, treatments, and organization levels (whole-plant, cellular, and molecular), and to identify the appropriate correlations among them, a clear conceptual framework is required. Similar to other stress responses, the molecular nature of the signals evoked after the onset of salt stress seems to be general, as with that observed in response to many other stimuli, and should not be considered to confer specificity per se. The focus of the current review is therefore on the temporal patterns of signals conveyed by molecules such as Ca 2+ , H + , reactive oxygen species, abscisic acid, and jasmonate. We propose that the outcome of the salinity response (adaptation versus cell death) depends on the timing with which these signals appear and disappear. In this context, the oftenneglected non-selective cation channels are relevant. We also propose that constraining a given signal is as important as its induction, as it is the temporal competence of signalling (signal on demand) that confers specificity.

Salinity often suppresses the wheat performance. As wheat is designated as silicon (Si) accumulator, hence Si application may alleviate the salinity induced damages. With the objective to combat the salinity stress in wheat by Si application (0, 50, 100, 150 and 200 mg L -1 ) using calcium silicate, an experiment was conducted on two contrasting wheat genotypes (salt sensitive; Auqab-2000 and salt tolerant; SARC-5) in salinized (10 dS m -1 ) and non-salinized (2 dS m -1 ) solutions. Plants were harvested 32 days after transplanting and evaluation was done on the basis of different morphological and analytical characters. Silicon supplementation into the solution culture improved wheat growth and K + /Na + with reduced Na + and enhanced K + uptake. Concomitant improvement in shoot growth was observed; nonetheless the root growth remained unaffected by Si application. Better results were obtained with 150 and 200 mg L -1 of Si which were found almost equally effective. It was concluded that SARC-5 is better than Auqab-2000 against salt stress and Si inclusion into the solution medium is beneficial for wheat and can improve the crop growth both under optimal and salt stressful conditions.

Salt-tolerant isolates Bacillus pumilus, Pseudomonas mendocina, Arthrobacter sp., Halomonas sp., and Nitrinicola lacisaponensis isolated from high saline habitats exhibited plant growth-promoting traits like P solubilization and indole acetic acid (IAA), siderophore, and ammonia production. These isolates were inoculated in wheat to assess microbe-mediated responses and plant growth promotion in salt affected soil. Maximum shoot and root length (33.8 and 13.6 cm) and shoot and root biomass (2.73 and 4.48 g dry weight) was recorded in plants inoculated with B. pumilus after 30 days. Total chlorophyll content was maximum in the leaves of the plants treated with Halomonas sp. (24.22 mg g−1 dry weight) followed by B. pumilus (23.41 mg g−1 dry weight) as compared to control (18.21 mg g−1 dry weight) after 30 days. Total protein content was maximum in Arthrobacter sp. inoculated plant leaves (3.19 mg g−1 dry weight) followed by B. pumilus (2.47 mg g−1 dry weight) as compared to control (2.15 mg g−1 dry weight) after 30 days. Total carotenoid content was maximum in plants inoculated with Halomonas sp. (1,075.45 and 1,113.29 μg g−1 dry weight) in comparison to control (837.32 and 885.85 μg g−1 dry weight) after 15 and 30 days. Inoculation of bacterial isolates increased presence of individual phenolics (gallic, caffeic, syringic, vanillic, ferulic, and cinnamic acids) and flavonoid quercetin in the rhizosphere soil. The concentration of IAA in rhizosphere soil and root exudates was also higher in all treatments than in control. Accumulation of phenolics and quercetin in the plants played a cumulative synergistic role that supported enhanced plant growth promotion of wheat in the stressed soil.

Fresh groundwater resources in Egypt contribute to some 20% of the total potential of water resources in Egypt. The Ministry of Water Resources and Irrigation (MWRI) increasingly recognizes its importance in the overall water resources management. The need for a more comprehensive groundwater management approach has led to the establishment of the Groundwater Sector (GWS) in December 1999. The GWS is now the sole responsible governmental agency for management of all groundwater resources and related water resources. The mandate of the GWS is: formulating and implementing the general policy for developing and managing groundwater and related water resources (flash floods, rainwater harvesting and desalinated water) on the national, regional and sub-regional level. Desalination of brackish groundwater in Egypt has a great potential with respect to the availability of the resource. All major aquifer systems in Egypt contain vast quantities of brackish groundwater. The exploitation of this resource is still limited. With the current low price of brackish water desalination there is a growing interest towards its exploitation. Brackish water desalination plants in Egypt confirm the potential of this solution. Other uses for brackish groundwater that are being considered are agriculture (salt tolerant crops) and fisheries (shrimp farms). The elements of the vision for desalination of brackish groundwater are: environmental sustainability through recycling of water and re-infiltration; public-private partnerships for exploitation, especially in the tourism sector; private sector financing through accepted modalities (BOT, DBO, etc.). With the input of experience from the Netherlands through the GWS project a new program for desalination was started. This program aims to provide the necessary concepts and data on desalination of brackish groundwater in Egypt to allow the GWS to formulate a clear policy in this regard.