Photosynthesis performance, antioxidant enzymes, and ultrastructural analyses of rice seedlings under chromium stress

摘要

The present study was conducted to examine the effects of increasing concentrations of chromium (Cr6+) (0, 25, 50, 100, and 200 mu mol) on rice (Oryza sativa L.) morphological traits, photosynthesis performance, and the activities of antioxidative enzymes. In addition, the ultrastructure of chloroplasts in the leaves of hydroponically cultivated rice (O. sativa L.) seedlings was analyzed. Plant fresh and dry weights, height, root length, and photosynthetic pigments were decreased by Cr-induced toxicity (200 mu M), and the growth of rice seedlings was starkly inhibited compared with that of the control. In addition, the decreased maximum quantum yield of primary photochemistry (Fv/Fm) might be ascribed to the decreased the number of active photosystem II reaction centers. These results were confirmed by inhibited photophosphorylation, reduced ATP content and its coupling factor Ca2+-ATPase, and decreased Mg2+-ATPase activities. Furthermore, overtly increased activities of antioxidative enzymes were observed under Cr6+ toxicity. Malondialdehyde and the generation rates of superoxide (O2I") also increased with Cr6+ concentration, while hydrogen peroxide content first increased at a low Cr6+ concentration of 25 mu M and then decreased. Moreover, transmission electron microscopy showed that Cr6+ exposure resulted in significant chloroplast damage. Taken together, these findings indicate that high Cr(6+)concentrations stimulate the production of toxic reactive oxygen species and promote lipid peroxidation in plants, causing severe damage to cell membranes, degradation of photosynthetic pigments, and inhibition of photosynthesis.