Effects of Drought Stress on Protective Enzymes Activities and Membrane Lipid Peroxidation in Leaves of Soybean Seedlings

The effects of drought stress on the protective enzymes activities and membrane lipid peroxidation in leaves of soybean seedlings and their relations with drought tolerance were studied using two drought-tolerant cultivars.The results showed that under severe drought stress,permeability of plasma membrane and content of malondialdephyde(MDA)increased gradually,and activities of superoxide dismutase(SOD),peroxidase(POD),catalase(CAT)increased first then decreased.Under mild drought stress,permeability of plasma membrane and content of MDA increased a little,while,under severe drought stress,the increasing was significant or very significant.The correlation analysis showed that there was a highly significant positive correlation between content of MDA and permeability of plasma membrane.The activities of SOD and CAT were the highest at the second day and the third day respectively,then decreased,obviously lower than that of the control at the sixth day;but the activity of POD being the highest at the third or fourth day,then decreased,still higher than that of the control at the sixth day,maintaining high level.The drought-tolerant cultivars had lower permeability of plasma membrane and content of MDA than the drought-sensitive,with higher activities of SOD,POD and CAT.