Phytotoxicity of cadmium ions on germinating seedlings of mung bean (<i>Phaseolus vulgaris</i>): Involvement of lipid peroxides in chlorphyll degradation

Abstract

Germinating seedlings of mung bean ( Phaseolus vulgaris L. cv. K‐16) were treated with different concentrations of cadmium acetate (10, 50 and 100 μ M ). Cd 2+ lowered the chlorophyll and heme levels. The level of lipid peroxides were higher on day 3 than on day 6. However, Cd 2+ treatment significantly enhanced the level of lipid peroxides. Similarly, a dose‐dependent induction of lipoxygenase (EC 1.13.11.12) activity was observed with Cd 2+ treatment. Further, the activities of antioxidant enzymes such as superoxide dismutase (EC 1.15.1.1) and catalase (EC 1.11.1.6) were decreased. Our results suggest that lipoxygenase‐mediated accumulation of lipid peroxides on the one hand and inhibition of free radical scavenging enzymes like superoxide dismutase and catalase on the other caused a pronounced reduction in the chlorophyll and heme levels of the seedlings. The experiments conducted on the effect of Cd 2+ on dark‐grown seedlings did not conform with the result of light‐grown seedlings. Though chlorophyll and heme levels decreased in a dose‐dependent manner, no accumulation of lipid peroxides was observed, suggesting that the inhibition of chlorophyll synthesis by Cd 2+ is achieved both by reaction with constituent biosynthetic enzymes as well as peroxide‐mediated degradation.