Changes in Physiological and Biochemical Indicators of Soft Wheat Leaves at the Initial Stage of Salt-Alkaline Stress

In the first hours of development of salt-alkaline stress in the leaves of Kamenka variety spring wheat (Triticum aestivum L.), changes in the content of water, proline, organic (malic, citric, succinic) acids, and activity of peroxidases and catalase were studied. The two-factor experiment included variants with NaCl salinity (50, 100, 150, 200 mM), alkalinity (pH 7–10) and variants with combined effects of NaCl and pH. The separate and mutual effects of stress factors on the height and mass of the above-ground part of plants; the content of water, proline, and organic acids in leaves; and enzyme activity were established using a two-factor analysis of variance with the determination of the strength of influence according to Snedecor. After 24 and 48 h of stress exposure, changes in height and weight were minimal, and the strength of the influence of stress factors was 8–11%. Under the influence of separate and mutual action of salinity and pH, the water content in the leaves decreased, while the overall impact of stress factors ranged from 17 to 28%. Changes in leaf proline levels were relatively equally dependent on salinity, pH values, and the interaction of these factors; over the observation period, the overall effect of stress factors increased from 54 to 77%. The increase in the total content of citric, malic, and succinic acids was equally influenced by individual stress factors and their mutual effect; the total strength of their influence during the observation period increased from 66 to 99%. Catalase activity of wheat leaves decreased during the first observation period (1 h), then the enzyme activity gradually recovered. The catalase activity of leaves was influenced to a greater extent by the factor of high pH values. The increase in peroxidase activity of leaves depended equally on individual stress factors and their mutual action. During the observation period, the total effect of salt-alkaline stress factors on the peroxidase activity of leaves decreased from 93–97% (1 and 4 h) to 79% (24 h). It is concluded that, at the initial stage of development of salt-alkaline stress, the main adaptation processes include the accumulation of organic acids and the activation of peroxidases in wheat leaves.