Oxidative Stress Induced by Lead in Chloroplast of Spinach

Seedlings of spinach were grown in Hoagland's medium containing 0, 20, 40, 60, 80, 100 microM PbCl2, respectively, for 4 weeks. Chloroplasts were assayed for overproduction of reactive oxygen species (ROS) such as superoxide radicals (O2(*-)) and hydrogen peoxide (H2O2) and of lipid peroxide (malonyldialdehyde) and for activities of the antioxidant enzymes such as superoxide dismutase, catalase, ascorbate peroxidase, and guaiacol peroxidase and glutathione content, oxygen-evolving rate, and chlorophyll content. Increase in both ROS and lipid peroxide content and reduction in photosynthesis and activities of the antioxidant defense system indicated that spinach chloroplast underwent a stress condition due to an oxidative attack. Seedling growth cultivated in containing Pb2+ media was significantly inhibited. The results imply that spinach chloroplast was not able to tolerate the oxidative stress induced by Pb2+ due to having no effective antioxidant defense mechanism.