FUNCTIONING OF NADPH+-DEPENDENT MALATE DEHYDROGENASE IN WHEAT LEAVES UNDER SALT STRESS
The economic humans functioning changes the biogenesis of the ecosystem over time. Irrational use of land resources generates drought, salinization, and an increase in the radioactive background. This negatively affects soil fertility and the quality of plants growing on them. Salinity of the soil with salts is one of the main environmental factors that can limit the growth and development of plants and can lead to a decrease in the yield and quality of crops. Despite salinity, plants develop complex tolerance mechanisms to adapt to salinity in soils, including physiological and biochemical responses that differ at the species level. Plants use mechanisms to relieve abiotic stress by reducing water loss and limiting water uptake. In addition, plants minimize the adverse effects of Na+ ion stress by excreting Na<sup>+</sup> from leaf tissues and by compartmentalizing Na<sup>+</sup> to a large extent in the vacuole. Despite these mechanisms, salt stress reduces crop yields and adversely affects all metabolic processes in the body, including photosynthesis. NADP<sup>+</sup>-dependent malate dehydrogenase catalyzes the reduction of malate to oxaloacetate in combination with the reduction of nicotinamide coenzyme. This enzyme is involved in the mechanism of fixation and transport of CO<sub>2</sub> and in the regeneration of NADPH for biosynthetic processes, the operation of the malate-aspartate shuttle and the maintenance of redox balance. And also, it can respond to stressful influences. We studied the dynamics of NADP<sup>+</sup>-MDH activity in green leaves of wheat (Triticum aestivum) under salt stress. When exposed to salt stress, a sharp increase in enzyme activity was shown in the first 6 hours of exposure, the peak of which falls on 3 hours. The activity of NADP<sup>+</sup>-MDH increases almost 8 times compared to normal values. However, after 24 hours of exposure, the activity of wheat malate dehydrogenase decreases below normal values. The change in the relative level of transcripts of genes encoding MDH generally corresponds to the dynamics of enzyme activity, reaching its maximum at 3 hours of exposure to NaCl. This fact allows us to conclude that there is a change in nadp-mdh expression as the main mechanism for changing the functioning of the enzyme.