Response of antioxidative enzymes in cucumber chloroplasts to cadmium toxicity

Solution culture experiments were conducted to investigate the effects of cadmium (Cd) toxicity on growth of cucumber seedlings, chlorophyll content, and net photosynthetic rate in leaves, activities of antioxidant enzymes, and contents of glutathione (GSH) and ascorbic acid (ASA) in purified intact chloroplasts. Results showed that lengths of main root and hypocotyl, weights of shoot and root, the root/shoot ratio, chlorophyll content, and net photosynthetic rate decreased significantly with increasing Cd level from 0 to 100mumolL(-1) in nutrient solution. Levels of malondialdehyde (MDA), H2O2, and O-2 in chloroplasts increased with increasing Cd concentration in solution. In the antioxidant defense system of chloroplasts, the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR), and the contents of GSH and ASA decreased with increasing Cd concentration in the nutrient solution. The results suggest that Cd interferes with the growth of cucumber seedlings by destroying chloroplast membrane integrity and decreasing chlorophyll content and net photosynthetic rate in leaves.