Control of Sucrose Metabolism in Polyethylene Glycol-stressed Carob (Ceratonia siliquaL.) Young Seedlings. The Role of Sucrose

Abstract

Four-d-old Ceratonia siliqua L. seedlings were treated with 30% PEG 4000 for several time periods, or with 26-5% and 25% PEG for 48 h. Drought stress was imposed on some seedlings in order to compare the results of stress due to drought with those due to the application of PEG. The water content of the axis and cotyledons and their osmotic potentials decreased with stress for the first 72 h and then remained constant, whilst dry weight increased after the first 24 h of imposed stress. Results imply the existence of an osmoregulation mechanism which was more pronounced when the stress was mild. Sucrose content increased with stress in both axes and cotyledons, and a negative correlation was found between osmotic potential and sucrose content in both embryo parts, suggesting the involvement of sucrose in the osmoregulation mechanism. Upon stress recovery sucrose content decreased and fructose accumulated in the axes. Sucrose synthetase activity was very low in cotyledons, while acid and alkaline invertase activity was too low to be measured. PEG-induced stress caused sucrose synthetase activity to decrease in both axes and cotyledons, while upon stress recovery sucrose synthetase activity increased. The activity of both invertases in the axes did not change significantly with stress. Correlation of sucrose content with sucrose synthetase activity suggests that this enzyme is involved in the control of osmoregulation in both parts of the embryo.