Halophytes, plants that survive to reproduce in environments where the salt concentration is around 200 mM NaCl or more, constitute about 1% of the worlds flora. Some halophytes show optimal growth in saline conditions; others grow optimally in the absence of salt. However, the tolerance of all halophytes to salinity relies on controlled uptake and compartmentalization of Na+, K+ and Cl- and the synthesis of organic compatible solutes, even where salt glands are operative. Although there is evidence that different species may utilize different transporters in their accumulation of Na+, in general little is known of the proteins and regulatory networks involved. Consequently, it is not yet possible to assign molecular mechanisms to apparent differences in rates of Na+ and Cl- uptake, in root-to-shoot transport (xylem loading and retrieval), or in net selectivity for K+ over Na+. At the cellular level, H+-ATPases in the plasma membrane and tonoplast, as well as the tonoplast H+-PPiase, provide the transmembrane proton motive force used by various secondary transporters. The widespread occurrence, taxonomically, of halophytes and the general paucity of information on the molecular regulation of tolerance mechanisms persuade us that research should be concentrated on a number of model species that are representative of the various mechanisms that might be involved in tolerance.

Salinity tolerance in halophytes

The environmental stress is a major area of scientific concern because it constraints plant as well as crop productivity. This situation has been further worsened by anthropogenic activities. Therefore, there is a much scientific saddle on researchers to enhance crop productivity under environmental stress in order to cope with the increasing food demands. The abiotic stresses such as salinity, drought, cold, and heat negatively influence the survival, biomass production and yield of staple food crops. According to an estimate of FAO, over 6 % of the world’s land is affected by salinity. Thus, salinity stress appears to be a major constraint to plant and crop productivity. Here, we review our understanding of salinity impact on various aspects of plant metabolism and its tolerance strategies in plants.

Effect of salinity stress on plants and its tolerance strategies: a review.

Plant proteome changes under abiotic stress--contribution of proteomics studies to understanding plant stress response

The dominance of salt water across the surface of the earth has lead to the widespread occurrence of salt-affected soils. Salt-tolerant plants (halophytes) have evolved to grow on these soils, with halophytes and less tolerant plants showing a wide range of adaptations. However, most of our crops are salt-sensitive. Consequently, salinity is an ever-present threat to agriculture, especially in areas where secondary salinisation has developed through irrigation or deforestation. Attempts to improve the salt tolerance of crops have met with very limited success, due to the complexity of the trait, both genetically and physiologically. Tolerance shows all the characteristics of a multigenic trait, with quantitative trait loci (QTLs) identified in barley, citrus, rice and tomato. Attempts to produce salt-tolerant crops have involved both the domestication of halophytes and the manipulation of existing crop species through conventional breeding programmes, the use of in vitro selection, pooling physiological traits, interspecific hybridisation, the use of marker-aided selection and the development of transgenic plants. After 10 years of research, the value of using transgenic plants to alter salt tolerance has yet to be tested in the field. The use of physiological traits in breeding programmes and the domestication of halophytes currently offer viable alternatives to the development of tolerance through the use of transgenic technologies.

Why does salinity pose such a difficult problem for plant breeders

Drought and salinity are the main abiotic stresses limiting crop yield and quality worldwide. Improving food production in drought- and salt-prone areas is the key to meet the increasing food demands in near future. It has been widely reported that silicon (Si), a second most abundant element in soil, could reduce drought and salt stress in plants. Here, we reviewed the emerging role of Si in enhancing drought and salt tolerance in plants and highlighted the mechanisms through which Si could alleviate both drought and salt stress in plants. Silicon application increased plant growth, biomass, photosynthetic pigments, straw and grain yield, and quality under either drought or salt stress. Under both salt and drought stress, the key mechanisms evoked are nutrient elements homeostasis, modification of gas exchange attributes, osmotic adjustment, regulating the synthesis of compatible solutes, stimulation of antioxidant enzymes, and gene expression in plants. In addition, Si application decreased Na+ uptake and translocation while increased K+ uptake and translocation under salt stress. However, these mechanisms vary with plant species, genotype, growth conditions, duration of stress imposed, and so on. This review article highlights the potential for improving plant resistance to drought and salt stress by Si application and provides a theoretical basis for application of Si in saline soils and arid and semiarid regions worldwide. This review article also highlights the future research needs about the role of Si under drought stress and in saline soils.

Mechanisms of silicon-mediated alleviation of drought and salt stress in plants: a review.

Saline soils are the major problem of cultivated lands of Iran. Suaeda aegyptiaca is a salt-tolerant plant (halophytes) that grow naturally in salt-affected areas of Iran. We have employed proteomics to identify the mechanisms of salt responsiveness in leaves of S. aegyptiaca grown under different salt concentrations. Ten-day-old plants were treated with 0, 150, 300, 450, and 600 mM NaCl. After 30 days of treatment, leaf samples were collected and analyzed using 2-D-PAGE. Out of 700 protein spots reproducible detected within replications, 102 spots showed significant response to salt treatment compared to 0 mM NaCl. We analyzed expression pattern of salt-responsive proteins using a hierarchical and two nonhierarchical (Fuzzy ART and SOM) statistical methods and concluded that Fuzzy ART is the superior method. Forty proteins of 12 different expression groups were analyzed using LC/MS/MS. Of these, 27 protein spots were identified including proteins involved in oxidative stress tolerance, glycinebetain synthesis, cytoskeleton remodeling, photosynthesis, ATP production, protein degradation, cyanide detoxification, and chaperone activities. The expression pattern of these proteins and their possible roles in the adaptation of S. aegyptiaca to salinity is discussed.

Effects of salinity levels on proteome of Suaeda aegyptiaca leaves.

This investigation was carried out to determine the effects of gamma radiation on germination and physiological characteristics of wheat seedlings. Two wheat genotypes (Roshan and T-65-58-8) were irradiated with 100, 200, 300 and 400 Gy. The results showed that MGT (Mean Germination Time), root and shoot length, and seedling dry weight decreased with increasing radiation doses but final germination percentage was not significantly affected by radiation doses. Biochemical differences based on proline content revealed that seedling irradiated at 100 Gy contained highest amount of proline (1.71 mg/g FW), whereas only 0.92 mg/g FW of proline was detected in nonirradiated seedlings. The highest amount of total chlorophyll content was obtained in seedlings irradiated at 100 Gy. Furthermore, the concentration of chlorophyll a was higher than chlorophyll b in both irradiated and non-irradiated seedlings. Chlorophyll and proline contents, and root and shoot dry weights in cv. Roshan were higher than those in T-65-58-8 mutant. These results show that the up-regulation of some physiological characteristics and seedling growth of wheat following gamma radiation treatment may be used for aboitic control such as drought and salt stress.

Effects of gamma radiation on germination and physiological aspects of wheat (triticum aestivum l.) seedlings

In order to study the effects of salinity and silicon application on root characteristics, growth, proline content, leaf and root ion accumulation of purslane (Portulaca oleracea L.), a greenhouse experiment was conducted at Ferdowsi University of Mashhad, Iran. The experiment was carried out in a split plot design in which levels of salinity (0, 120 and 240 mM) were allocated as main plots and silicon application of 1 mM sodium silicate and no application assigned as subplots with three replications. The results indicated that salinity caused a reduction in root growth (volume, area, diameter, total and main length and root dry weight), and shoot biomass accumulation. Both root and leaf sodium (Na) content and leaf proline content increased with increasing salinity. Leaf and root potassium (K) content decreased with increasing salinity. Application of silicon improved root area, root dry weight, and leaf and root K content in the presence of salinity. It also caused a significant reduction in leaf Na con...

Effect of salinity and silicon on root characteristics, growth, water status, proline content and ion accumulation of purslane (Portulaca oleracea L.)

Cardinal temperatures for germination of Kochia scoparia (L.)

Saffron (Crocus sativus) production and processing , Saffron (Crocus sativus) production and processing , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Mohammad Kafi

Papers

Effects of salinity levels on proteome of Suaeda aegyptiaca leaves.

Effects of gamma radiation on germination and physiological aspects of wheat (triticum aestivum l.) seedlings

Effect of salinity and silicon on root characteristics, growth, water status, proline content and ion accumulation of purslane (Portulaca oleracea L.)

Cardinal temperatures for germination of Kochia scoparia (L.)

Saffron (Crocus sativus) : Production and Processing