Effect of Cadmium on Chlorophyll Content, Lipid Peroxidation and some Antioxidative Enzymes in the Leaf of Maize (Zea Mays)

Cadmium is a heavy metal which at even low concentration is toxic to plants. We investigated the effects of varying cadmium concentrations on the anti-oxidative defence mechanism in the leaves of Zea mays seedlings. The soil sample used was divided into five groups containing four replicates each. Group one was uncontaminated. Groups two to five were contaminated with varying concentrations of cadmium chloride, ranging from 5mg, 10mg, 20mg and 30mg respectively. The leaf sample from each group was taken for weekly analysis starting from the third week after planting. The anti -oxidative defence enzymes determined were catalase, peroxidase, superoxide dismutase and thiobarbituric acid reactive species as indice for lipid peroxidation. Also determined were the leaf weight, leaf area and chlorophyll content of the leaves. Statistical analysis using SPSS showed that varying cadmium concentrations in the soil significantly (p<0. 05) reduced the leaf area, chlorophyll content and weight of the leaves in Zea mays. An extremely significant (p< 0.05) loss of chlorophyll content and reduction in leaf area was observed in weeks 4, 5 and 6 under varying concentrations of cadmium exposure. With regards to the distribution of cadmium in leaves, the obtained data showed that there was no significant (p> 0.05) difference between the cadmium concentrations of 20mg and 30mg in weeks 5 and 6. Furthermore, a significant (p< 0.05) increase was observed in the anti-oxidative enzymes in response to varying concentrations of cadmium exposure when compared with the control. A significant (p < 0.05) increase was observed in catalase and peroxidase activity of weeks 5and 6 under varying cadmium exposure. A significant (p<0. 05) increase was also observed in superoxide dismutase activity and malondialdehyde levels (in response to increased lipid peroxidation) of weeks 4, 5 and 6 under varying concentrations of cadmium exposure. The increased production of anti-oxidative enzymes observed in the leaf of Zea mays is to ameliorate the effects of oxidative stress caused by cadmium toxicity.