The effect of chloride salinity on growth and physiological processes in mid-ripening varieties of Solanum tuberosum L. plants

Significant expansion of saline territories due to climate aridization and man-made pressure on the environment reduces the productivity of the most important crops. The intense salinity affects the basic physiological processes of plants, inhibiting growth and reducing productivity. In response to salt stress, the plant responds with multiple molecular, metabolic and physiological reactions aimed at the formation of protector systems and the organism adaptation to stressful environmental conditions. The potato ranks fourth among the major world food crops and its production is very important for ensuring food security and social stability in many countries. Wild potato species are highly tolerant to stress, however, modern varieties are the product of a long-term breeding, significantly more susceptible to salinization. All this raises the question of the need to study the potato tolerance to salt stress and to specify criteria for selecting the most commercially viable varieties. This cannot be done without comparing salt tolerance physiological mechanisms for economically valuable genotypes. We studied the physiological (the level of photosynthetic pigments in leaves, content of proline and lipid peroxidation degree in leaves, stem and roots) and growth (the length of axial organs, leaf surface area, wet and dry biomass) parameters of cv. Lugovskoy and ст. Nakra potato plants exposed to chloride salinity of different intensity (50-150 mM NaCl). We obtained disease-free regenerants of potato plants in vitro by the method of microclonal propagation and adapted them on Murashige and Skoog medium (0.5 MS) with half the content of macro- and microelements during 21 days. After growing on a hydroponic unit, the plants were transferred to the same medium with the addition of NaCl. The plants were fixed and used for the assays 7 days after the beginning of the experiment. The leaves of the middle layers, middle parts of the stem and roots were fixed with liquid nitrogen to determine the amount of proline and assess the intensity of lipid peroxidation; 96% ethanol was used to determine the level of photosynthetic pigments in plant leaves. We evaluated morphometric parameters on at least 10 plants for each variant. The results of the studies showed differences in the salt tolerance between two varieties of potatoes. Growth parameters of cv. Lugovskoy plants exceeded cv. Nakra plants in the absence of stress (See Table). Low intensity of salinity (50 mM) had a pronounced negative effect on cv. Nakra stolon formation; concentration increasing to 150 mM suppressed the stolon formation and decreased the area of the assimilating surface, to a greater degree, for cv. Lugovskoy plants (See Table). One of the most negative effects of salinization affecting the assimilating apparatus of plants is the inhibition of the level of photosynthetic pigments. The contents of all pigment groups were similar for the two varieties, the negative influence of NaCl in the calculation on the dry weight began at a concentration of 100 mM. For cv. Lugovskoy, the negative effect of salinity was less pronounced (See Fig. 1). Salinity as well as other types of abiotic stress increases ROS production. The lipid peroxidation degree in potato plants of the cv. Nakra without stressor was higher than that of cv. Lugovskoy (See Fig. 2). Under salt condition, the content of MDA in the reaction approximately increased by 32-40% with the use of leaf extracts of cv. Nakra S. tuberosum, as compared to the control plants; in leaf extracts of cv. Lugovskoy, an increase in the content of MDA was approximately 300 %. There was no change in the level of MDA in the stems and roots of two varieties under chloride salinity compared to the control plants, except for root extracts of cv. Nakra 150 mM NaCl (See Fig. 2). Proline accumulation is one of the most marked changes in plant metabolism in response to salt stress. Proline distribution in potato plant parts was different: for cv. Nakra the maximum level was reached in the leaves and the minimum - in the roots, for cv. Lugovskoy the maximum level was observed in the stems and the minimum - in the roots (See Fig. 3). Weak and moderate (50 and 100 mM) chloride salinity activated the accumulation of proline, largely, in cv. Lugovskoy potato plants, and intensive (150 mM) salinization - in cv. Nakra plants (See Fig. 3). The obtained results can be useful for developing a technology to improve salt tolerance of the studied cultivars and to opt for the most commercially viable variety. The paper contains 3 Figures, 1 Table and 24 References.