Research Article Biochemical Studies on the Effects of Zinc and Lead on Oxidative Stress, Antioxidant Enzymes and Lipid Peroxidation in Okra (Hibiscus esculentus cv. Hassawi)
Magdy M. Youssef and
Mohamed M. Azooz
Abstract:Hibiscus esculentus plants were grown in 5, 10, 20 and 40 mM of Zn2+ or/and Pb2+ for 4 weeks. The treated Hibiscus esculentus plants were analyzed with focus on the effects of Zn2+ or/and Pb2+ on antioxidant enzymes and antioxidants in shoots. An enhanced level of lipid peroxidation and an increased of hydrogen peroxide (H2O2) in shoots indicated that Zn2+ or/and Pb2+ caused oxidative stress in Hibiscus esculentus plants. Zn2+ or/and Pb2+ induced a diminish in superoxide dismutase (SOD) activity, whereas catalase (CAT) was significantly increased. Glutathione peroxidase (GPOD) activity decreased, enhancement in glutathione reductase (GR) activity was recorded more at 20 and 40 mM than at 5 and 10 mM Zn2+ or/and Pb2+. While, ascorbate peroxidase (APOD) exhibit maximum stimulation at high concentrations of Zn2+ or/and Pb2+ in shoots. Augmented activities of some antioxidant enzymes in Zn2+ or/and Pb2+ treated plants propose that they have some additive function in the mechanism of metal tolerance in Hibiscus esculentus plants. The levels of reduced glutathione (GSH) in shoots of Hibiscus esculentus plants treated with Zn2+ or/and Pb2+ were declined. Zn2+ or/and Pb2+ decreased the amount of glutathione disulphide (GSSG) as a whole and this decrease was concentration-dependent. Ascorbate (AS) level was augmented slightly at lower levels but decreased at higher levels of Zn2+ or/and Pb2+, while increments in dehyroascorbic acid (DAS) content was observed at either 20 or 40 mM of Zn2+ or/and Pb2+. Therefore, the AS/DAS relation declined with Zn2+ or/and Pb2+ treatment.