Chromium (VI) induced changes in growth and root plasma membrane redox activities in pea plants

The effect of chromium (Cr) on growth as well as root plasma membrane redox reactions and superoxide radical production was studied in pea (Pisum sativum L. cv. Azad) plants exposed for 7 days to 20 and 200 mu M Cr (VI), respectively, supplied as potassium dichromate. The growth of pea plants declined significantly at 200 mu M Cr, as indicated by reduced leaf area and biomass. Relative to the control plants (no Cr exposure), the Cr content of roots increased significantly, both at 20 and 200 mu M Cr. Following exposure to 200 mu M Cr, there was a significant increase in root lipid peroxidation and hydrogen peroxide (H2O2) content, while both the Fv/Fm ratio and chlorophyll content were reduced. Exposure to Cr increased NADPH-dependent superoxide production in pea root plasma membrane vesicles, with the effect being more significant at 200 mu M Cr than at 20 mu M Cr. Treatment with Cr rapidly increased the activities of NADPH oxidase: relative to the controls, plants exposed to 20 mu M Cr showed approximately a 67% increase in activity while there was a threefold increase in those plants exposed to 200 mu M Cr. NADH-ferricyanide oxido-reductase activity was found to be inhibited by 16 and 51% at 20 and 200 mu M Cr, respectively. The results of this study suggest that exposure to excess Cr damages pea root plasma membrane structure and function, resulting in decreased photosynthesis and poor plant growth.