Oxidative stress and change in plant metabolism of maize (Zea mays L.) growing in contaminated soil with elemental sulfur and toxic effect of zinc

Responses of the chlorophyll, antioxidant enzymes and lipid peroxidation in maize growing in soil with zinc (Zn) and elemental sulfur (S) were studied. The results showed that sulfur alleviated the high toxicity of Zn and increased the concentration of chlorophyll. The activities of superoxide dismutase (SOD) and peroxidase (POD) increased significantly and catalase (CAT) activity significantly decreased in plants treated with 1000 mg/kg Zn alone. Compared with the control, SOD and POD activity increased from 62.3 to 77.3 U/mg protein and 28 to 41 nmol/min/mg protein, respectively. However, CAT activity decreased from 1.96 to 1.48 mu mol H2O2/min/mg protein. The concentration of malondialdehyde (MDA) in maize leaves significantly increased as the concentration of Zn increased. Moderate concentrations of S (32 and 160 mg/kg) alleviated the increase of both SOD and POD activity and the decrease of CAT activity that were observed under conditions of Zn stress. The greatest decrease of SOD and POD activity were 17% and 21% and both were observed in the treatment of 160 mg/kg S combined with 1000 mg/kg Zn. In this treatment, the greatest increase of CAT activity (11%) was also observed. The results suggest that moderate supplementation with S may ameliorate the toxicity caused by excess Zn and plays an important role in protecting plants from oxidative stress induced by excess Zn.