Ryshakova O. Carbohydrate metabolism indicators in lines of maize contrasting for drought tolerance during germination in the conditions of water deficiency and hyperthermia

The thesis is devoted to the study of biochemical features of drought tolerance of maize (Zea mays L.) according to the characteristics of carbohydrate metabolism, abscisic acid content and activity of soluble lectins. It was found that the genotypes of a model samplimg of self-pollinated maize lines, contrasting for drought tolerance, content of the stress hormone (abscisic acid), activity of carbohydrate-binding proteins (soluble lectins), and indicators of carbohydrate metabolism, respond in a different way to stress factors. In particular, the accumulation of abscisic acid and the activation of soluble lectins with a molecular weight of 50-60 kDa under conditions of water deficiency and hyperthermia in drought-resistant maize lines have been demonstrated. Monosaccharide content in the conditions of water deficiency and hyperthermia increased, probably due to their osmoregulatory and signaling functions in adaptive processes of the plant cell. It was demonstrated that the functioning of sucrose phosphate synthase varies significantly in the studied genotypes of maize in the conditions of water stress and hyperthermia: the enzyme is activated in resistant genotypes in the conditions of short-term water deficiency, and is inhibited in non-resistant ones. At the same time, sucrose accumulation and increase in the sucrose/disaccharide ratio in drought tolerant genotypes were noted. It was found that during grain germination in the conditions of water deficiency, hexokinase and transketolase enzyme activity in the tissues of the drought tolerant line of maize increased at the initial germination periods; while in the caryopsis of the drought-intolerant line, there was a reliable and stable decrease in the enzyme activity. The increase in the activity of sucrose phosphate synthase, hexokinase, transketolase, and isocitrate dehydrogenase in the conditions of water deficiency and hyperthermia in the tissues of germs of drought-tolerant lines of maize is an evidence of the sequential activation of all stages of carbohydrate metabolism in the tissues of these lines and their inhibition in the tissues of germs of weakly drought-tolerant lines under such stress factors. Based on the studies, a model of functioning and interaction of biochemical reactions during formation of protective response and resistance to abiotic factors is proposed. The data obtained are theoretical substantiation to use the results of the study to develop the methods for selecting drought-tolerant maize lines.