Features of leaf photosynthetic apparatus of sugar beet under retardants treatment

Abstract

We studied the influence of antigibberellin compounds with different mechanisms of action-Paclobutrazole (0.05%) and Dextrel (0.3%) on the formation of leaf surface, structure of photosynthetic apparatus and features of leaf functioning under retardants artificial growth control on sugar beet plants. We found that retardants treatment slowed the growth of total leaf surface of sugar beet. At the same time, application of Paclobutrazole (0.05%) caused a greater retardation effect on plant growth. The number of dead leaves of treated plants during vegetation season was unchanged compared to control. We established that decrease in the leaf area was accompanied by their thickening due to increase in the size of palisade and spongy parenchyma cells, decrease in the size of epidermal cells and increase in the number of stomatas per unit leaf area. Stomatal index which characterizes the ratio of number of stomata form to the total number of epidermal cells on the same leaf area was identical for all experimental variants, notably, the ratio of stomata and other epidermal cells not changed under retardants application. The rate of photosynthesis of retardants-treated leaves was lower than in a control, and the proportion of respiratory processes in their carbon dioxide gas exchange was greater. Dextrel and Paclobutrazole differently influenced on the ratio of leaf and mesophilic resistances of CO2 diffusion and concentration of carbon dioxide in intercellular spaces, that indicates about different regulation of assimilation apparatus activity with their participation. Retardants are a powerful means to regulate the assimilation apparatus activity, one of the donor-acceptor system component, and can be used for the targeted regulation of plastic substances redistribution in sugar beet.