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The low rainfall and high temperatures of arid and semi-arid zones promote high salinity and this salinity has become an important factor limiting the growth of salt-sensitive plants. More than 800 million hectares of land throughout the world are salt affected including 39.2 million hectares in Russia, while in Kazakhstan, salinized soils occupy about 40% of the country's area. Phytoremediation with the use of halophytes can be a cost-effective and environmentally sound technology for the remediation of salt-impacted sites. Halophytes could be valuable sources of novel endophytic isolates that can be used to overcome various biotic and abiotic stresses such as salinity. Endophytes can contribute to plant health impeded by salinity stress, by influencing phytohormonal levels and signaling, contributing to homeostasis maintenance of toxic ions under salinity stress, enhancing photosynthesis, and contributing to biomass production and allocation. The review is devoted to halophytic plants and endophytic microorganisms inhabiting them. Data on the possibility of using halophytes for remediation of saline soils are presented. The definitions of which plants can be considered halophytes are given, the mechanisms of adaptation of halophytes to salinity conditions are described. Data on the use of halophytes for the production of agricultural and other valuable products on saline soils are presented. The list of halophytes of practical value and promising for agricultural use on saline soils of Russia and Kazakhstan is given. Endophytic bacteria inhabiting halophytic plants are described and the results of their practical use for obtaining agricultural products on saline soils and phytoremediation of highly saline soils are presented. The selection of compatible and effective plant-microbial systems and their use to combat abiotic and biotic stresses of plants and produce agricultural products on saline soils is a promising scientific direction. This will make it possible to develop methodological approaches to solving one of the global problems of agricultural production—salinization and degradation of agricultural lands and obtaining products on them and to offer practical ways to implement it. [ABSTRACT FROM AUTHOR]

Ion-exchanging properties of the polymeric matrix of the cell walls isolated from leaves were examined. The glycophyte 55-day-old plants of spinach (Spinacia oleracea L., cv. Matador) grown on a nutrient solution containing 0.5, 150, or 250 mM NaCl and the halophyte seepweed (Suaeda altissima (L.) Pall.) of the same age grown at 0.5, 250, or 750 mM NaCl were compared. The ion-exchange capacity of the cell walls was estimated at different pH and ionic strength of a solution. In the structure of the leaf cell walls, three types of cation-exchange groups were found, namely, two types of carboxylic groups (one of them belongs to galacturonic acid residue) and phenolic OH-groups. The quantities of the groups of each type and their ionization constants were determined. The qualitative composition of the ion-exchange groups in the leaf cell walls was found to be uniform in both plant species regardless of their nutrition. However, the quantity of the carboxylic groups of galacturonic acid depended on the ambient salt concentration in a different manner in the glycophyte and halophyte. This change in the composition of functional groups of cell wall polymers was more pronounced in the halophyte and is apparently one of the responses of these plants to salinization. The sharp increase in the NaCl concentration in the medium leads to a decrease in pH in the extracellular water space due to ion-exchange reactions between sodium ions coming from the external medium and protons of the ionized carboxylic groups of the cell walls. The results are discussed in the aspect of participation of the leaf cell walls in plant responses to salinization. [ABSTRACT FROM AUTHOR]

One of the pressing tasks of current biotechnology is the production of stress-resistant cultures of hairy roots and elaboration of procedures of their long-term storage without frequent passages and the use of expensive and labor-consuming methods of cryopreservation. Plant resistance to stress factors very much depends on their antioxidant system and its component glutathione-S-transferases. In this work, we describe the production and examination of tobacco (Nicotiana tabacum L.) hairy roots with constitutive expression of glutathione-S-transferase gene AtGSTF11 of Arabidopsis thaliana. Tobacco hairy roots carrying this transgene were notable for an intense accumulation of biomass and greater resistance to salinization, heavy metals, and heat stress. Moreover, transgenic hairy roots better survived long-term storage without passages to fresh nutrient medium. Constitutive expression of gene AtGSTF11 in the cultures of hairy roots under stress conditions was accompanied by a decrease in the content of hydrogen peroxide, proline, and malonic dialdehyde and was associated with a rise in the rate of superoxide anion production and total antioxidant capacity. [ABSTRACT FROM AUTHOR]

The technique that enables simultaneous evaluation of water potential in the substomatal cavity of the intact leaf (ψwа) and rate of its photosynthetic CO2/H2O gas exchange was applied to a halophyte Suaeda altissima (L.) Pall. Formation of a water-potential gradient in a whole plant, rate of CO2 uptake, rate of transpiration, and concentrations of Na+ and Cl– ions in the plant organs were determined under conditions of chloride–sodium salinization of a nutrient solution. It was found that the salinization decreases not only biological productivity of the plants but also their capacity to accumulate Cl– in the amounts equivalent to Na+ accumulation. High salinity also diminished the gradient of water potential between a nutrient solution and the apoplast of the cells in the leaf substomatal cavity due to the increase in ψwа and, respectively, decrease in the water stream from roots to leaves and the rate of CO2/H2O gas exchange of the leaf. It was shown that the decrease in the water potential in the interface between liquid and gaseous phases in the apoplast of the substomatal cavity (expressed in the ψwа value) plays an essential role in the regulation of water uptake under salinization conditions. It is supposed that the NaCl-induced increase in ψwа is a consequence of the suppression of photosynthesis and a resultant osmolyte shortage together with the decrease in plant productivity due to the stress impact exerted by NaCl. [ABSTRACT FROM AUTHOR]

The plants from two populations (P1 and P2) of xero-halophyte Sedobassia sedoides (Pall.) Freitag & G. Kadereit (Chenopodiaceae) with С3–С4 intermediate type of photosynthesis were examined. Morphophysiological parameters were determined: dry biomass of the above-ground organs, maximum quantum yield of photosystem II (PSII), ultra- and mesostructure of the leaf, carbon isotope discrimination (δ13С) in plants grown under normal conditions and exposed to moderate salinization (0 and 200 mM NaCl). By the values of δ13С and efficiency of PSII, we did not detect significant differences between the populations. Under control conditions, the chloroplasts and mitochondria were located in Kranz-like cells of the bundle sheath of both populations in the region adjacent to vascular bundle, which is characteristic of С2 type of photosynthesis (with photorespiratory СО2 concentrating mechanism). P2 plants were notable for a greater volume of Kranz-like cells of the bundle sheath and more numerous, larger chloroplasts and mitochondria than in P1 plants. By structural leaf parameters, P1 plants may be attributed to a proto-Kranz type of photosynthesis (intermediate between С3 and С2 types) and P2 plants to С2 photosynthesis. Under salinization, the accumulation of dry biomass was reduced in both populations but more considerably in P1. The ultrastructure of organelles in both populations showed different responses to salinization, which was especially pronounced in Kranz-like cells of the bundle sheath. In P1 plants, the area of chloroplasts and mitochondria rose, whereas the area and number of chloroplasts under stress did not change in P2 plants but the area and number of mitochondria decreased. In the cells of plants from both populations, signs of degradation were observed (more pronounced in P1 plants); they were shown in chloroplasts twisting and a disturbance of their granal stacking. In P2 plants, Kranz-like cells of the bundle sheath preserved safer organelles but there occurred the cells with complete degradation of a vacuolar type. Thus, intraspecific ultra- and mesostructural differences were detected in plants from two populations of С3–С4 intermediate species S. sedoides, which reflect different stages of development of photorespiratory СО2 concentrating mechanism. Under salinization, the plants from two different populations showed unlike strategies of adaptation on the level of leaf ultra- and mesostructure. [ABSTRACT FROM AUTHOR]

Flotillin membrane proteins are involved in many cellular processes and physiological functions. However, these proteins' participation in plant response to stresses remains poorly understood. In the present report, the possible involvement of flotillin Flot1 in Na+ and K+ homeostasis in cells under sodium chloride salinization of the medium was studied in Arabidopsis thaliana (L.) Heynh. For this purpose, the Flot1 gene transcription was analyzed in the roots and leaves of wild-type (WT) and flot1 mutant plants with a T-DNA insertion in the promoter using the quantitative Real Time-RT PCR (qRT-PCR). Along with this, a mutant phenotype was studied (growth characteristics, content of Na+ and K+ ions in organs, and ultrastructure of root cells) under normal conditions and in the presence of 100 mM NaCl in the culture medium. The mutation led to the activation of AtFlot1 expression, which was more noticeable in the roots during salinization. Under these conditions, the mutants had larger organ mass, lower Na+ content, and higher K+ content in organs than that of WT. The study of the ultrastructure of A. thaliana root cells in mutant plants showed more intensive formation of post-Golgi vesicles and multivesicular bodies (MVB) in the cytoplasm. In both mutant and WT plants, the presence of sodium chloride in the nutrient solution stimulated the formation of MVB and microvacuoles in the cytoplasm and fusion of the latters into larger structures. It is assumed that changes in the ultrastructure of root cells that are caused by mutation and salinization reflect the stimulation, respectively, of vesicular trafficking and biogenesis of vacuoles—processes involved in maintaining Na+ and K+ cell homeostasis. [ABSTRACT FROM AUTHOR]

The peculiarities of the prevalence of C4 species in the relief of the Kyzylkum Desert were revealed based on botanical and geographical descriptions. In the lowlands (0–50 m above sea level), a predominance of C3 halophytes was found, while halophytes with C4 photosynthesis began to predominate at medium elevations (50–200 m above sea level). Above 200 m above sea level, a sharp decline in the contribution of halophilic flora to the biodiversity of native vegetation was detected. Thus, the penetration of halophytes above 200 m is limited by the presence of C4 photosynthesis as an adaptive characteristic to soil desalinization. A decrease in the succulence of leaf morphology in edificatory perennial plants of the Kyzylkum Desert (tamarix, saxaul, and camel thorn) was noted with a decrease in soil salinization. In the summer dry period, C4 photosynthesis provides a competitive advantage over C3 halophytes for survival on desalinated soils of elevated parts of the terrain desiccated during the summer. It was concluded that the acquisition of C4 photosynthesis by halophilic species is an adaptation of the photosynthesis of halophilic flora to seasonal desalinization and drying of the soil of the elevated parts of the Kyzylkum Desert. [ABSTRACT FROM AUTHOR]

The ability of brassinosteroids, such as 24-epibrassinolide (EBL) to increase the resistance of oilseed rape plants ( Brassica napus L.) to salt stress (175 mM NaCl) was investigated along with the possible mechanisms of their protective action. Seedlings were grown for three weeks on the Hoagland-Snyder medium under controlled conditions. The experimental plants were treated with either (1) 175 mM NaCl, or (2) 10 M EBL, or (3) 175 mM NaCl plus 10 M EBL by adding the corresponding components to the growth medium. The exposure was 7 and 14 days. As compared to the control, salinization inhibited plant height by 33-35%, reduced leaf area by 2.0-2.5 times, reduced 2.5- and 2-fold plant fresh and dry weight, respectively, reduced water content of plant tissues by 26-31% and, twofold, the content of chlorophylls a and b. Plants responded to NaCl by developing oxidative stress conditions, lowering the osmotic potential of the cell contents down to −2 MPa, accumulating proline (by 43-52 times) and low-molecular-weight phenolics (by 1.9-2.7 times). Oilseed rape plants were shown to respond to salinization with an increase of endogenous content of steroid hormones: 24-epibrassinosteroids (24-epibrassinolide and 24-epicastasterone), 24S-methyl-brassinosteroids (brassinolide and castasterone), and 28-homobrassinosteroids (28-homobrassinolide and 28-homocastasterone); such evidence indirectly confirms the involvement of brassinosteroids in the development of salt tolerance. Adding EBL to the nutrient medium under optimal growth conditions did not significantly affect the indices under study. Under salt stress, EBL showed a pronounced protective effect: stem growth was fully restored, plant assimilation area increased by as much as 67-76% as compared to the control index, fresh and dry weight largely recovered (up to 85-92% of the control values), and the inhibitory effect of NaCl on photosynthetic pigments was diminished. Exogenous EBL impeded the development of NaCl-dependent lipid peroxidation and increased the osmotic potential of the leaf cell contents. The protective effect of EBL under salt stress was probably associated with EBL antioxidant effect, rather than the hormone-induced accumulation of proline and of low-molecula-weight phenolics, as well as with the ability to regulate water status by maintaining intracellular ion homeostasis. [ABSTRACT FROM AUTHOR]

Physiological characteristics of a novel strain of the halophilic alga Dunaliella salina IPPAS D-232 isolated from the hypersaline lake Razval (Sol-Iletsk, Orenburg region) were studied. It was shown that the extract from the cells of this strain manifested antioxidant properties and also antibacterial activity relative to opportunistic bacteria. The influence of medium stirring and salinity on the level of D. salina antioxidant activity was assessed: it was established that medium salinization (93 g/L) and continuous stirring favored the highest accumulation of D. salina IPPAS D-232 biomass. It was found that the extremely halophilic archaea Halorubrum tebenquichense and moderately halophilic bacterium Marinococcus halophilus stimulated D. salina development and increased its antioxidant activity. The results obtained expand our knowledge of specific ecological features of the studied microalgal species; they could form the basis for the development of new approaches to the mass cultivation of D. salina. [ABSTRACT FROM AUTHOR]

The avens ( Geum urbanum L.) seedlings were grown for 6 weeks until the expansion of five to six leaves and then exposed to salinity shock (300 mM NaCl in the nutrient medium) or to a gradual (within 4 days) increase in NaCl concentration from 100 to 400 mM. The dynamics of stress-dependent accumulation of Na+, Cl−, proline, and polyamines in leaves and roots was measured, together with activities of antioxidant enzymes, namely, superoxide dismutase (SOD) and guaiacol-dependent peroxidase occurring in soluble, ionically bound, and covalently bound forms. It is shown that avens plants can adapt to gradual salinization by mobilizing stressinducible protective mechanisms (accumulation of proline and spermine) and by activating constitutive enzyme systems (SOD and peroxidase). [ABSTRACT FROM AUTHOR]

The effects of NaCl, Na2SO4, and mannitol on mobilization of storage lipids in the cotyledon mesophyll and root meristem cells during the germination of purple alfalfa ( Medicago sativa L.) seeds were studied using the transmission electron microscopy technique. The ultrastructural analysis showed that the number and shape of specific organelles, oleosomes, depended on the osmotic effects of a salt used. In control seedlings grown on distilled water, lipid mobilization in roots terminated by the 4th day, and in cotyledons, only by the 8th day. The disruptions in the storage lipid mobilization in the treated seedlings were specific and depended on the stress agent used, the osmotic pressure induced by this agent, as well as on the tissue type. The presence of a great number of oleosomes in the cytoplasm of cells subjected to osmotic stress, in contrast to the control ones, demonstrated the inhibition of mobilization processes. All concentrations of Na2SO4 and mannitol suppressed lipid mobilization in the cotyledons and roots. At the same time, NaCl markedly suppressed this process in the root cells only at a higher osmotic pressure of the solution. The results obtained suggest that the cytological analysis of cotyledon storage-lipid mobilization can tentatively assess the resistance of dicotyledonous plants to abiotic stresses. [ABSTRACT FROM AUTHOR]

Effects of various combinations of nutrient solution salinity (0.3, 171, and 342 mM NaCl), photosynthetically active radiation (PAR) of 600 or 1150 μmol/(m2 s), and type of nitrogen nutrition (amide-N or nitrate-N) on the productivity and the content of accumulated mineral nutrients and free amino acids were studied in Salicornia europaea plants. At PAR of 600 μmol/(m2 s), plant productivity increased with elevation of salinity level; at 1150 μmol/(m2 s), the maximum productivity was observed in the plants grown at 171 mM of NaCl. The content of free amino acids in shoots, regardless of PAR, decreased with growing salinity level, whereas Na content, on the opposite, increased. Glutamic acid, rather than proline, was shown to be the main organic osmolyte in this plant species. Comparison of the productivity of plants grown on solutions with amide (urea) or nitrate nitrogen showed that higher biomass accumulation was achieved in the former case. [ABSTRACT FROM AUTHOR]

The effects of NaCl, putrescine (Put), and the combination of two agents on the contents of free polyamines (PA), peroxidase activity, and the ultrastructure of the mesophyll apoplast were studied in the third leaf pair of Mesembryanthemum crystallinum L. plants. The NaCl solution was added to soil daily for three days (100 ml of the 100 mM solution), and plants were sprayed with the 1 mM Put solution twice per day for a six-day period. The accumulation of Put and especially spermidine (Spd) by day 3 of salinization was followed by a dramatic drop in Put and Spd contents by day 6. In contrast, the activities of soluble and ion-bound peroxidases increased following a long lag-period. Treatments with Put and NaCl plus Put considerably enhanced this rise in two peroxidase activities. An electron microscopic examination of cell walls in the control and stressed plants demonstrated that a gap developed at the middle lamella with “pockets” filled with amorphous polysaccharides (AP), presumably pectins. At the maximum gap width, the pockets fused with the intercellular spaces, and, in this case, the intercellular spaces also contained AP. Following salinization, AP in the apoplast swelled and expanded. Apparently the genetic determination of high AP content in M. crystallinum plants is the basis for the ability of juvenile plants to bind Na+ and Cl– ions and excess PA and also to accumulate water. In the plants treated with NaCl plus Put, the number of pockets and their volume increased, and the surface of some cell walls became plated with suberin, thus providing an additional barrier for ion transport from the pockets and intercellular spaces into cells. The formation of suberin plates was correlated with the high activity of ion-bound peroxidase essential for suberin deposition. The authors presume that H2O2 results from PA oxidation and, in its turn, induces the activity of peroxidase involved in the suberin plate formation. [ABSTRACT FROM AUTHOR]

The heat production rate in the suspension of unicellular alga (Chlorella vulgaris) was studied by the method of microcalorimetry during adaptation of the alga to stress conditions (NaCl and 45°C). The heat production rate slightly increased after the addition of 75 mM NaCl to cell suspension. A two-phase response was observed at 150 and 450 mM NaCl and at elevated temperature. The heat production rate was high during the first 3–4 h; then, it decreased and leveled off. This characteristic dramatically decreased at a high salt concentration (500 mM). Cell was unable to adapt to a high NaCl concentration (550 mM), which led to energy dissipation manifested in a high heat production rate. We conclude that the heat production rate, an integral indicator of plant cell activity can be used to assess plant cell adaptation to the impact of stress factors. [ABSTRACT FROM AUTHOR]