Biochemical Adaptations in Zea mays Roots to Short-Term Pb(2+) Exposure: ROS Generation and Metabolism

The present study investigated the effect of lead (0, 16, 40 and 80 mg L(-1) Pb2+) exposure for 3, 12 and 24 h on root biochemistry in hydroponically grown Zea mays (maize). Pb2+ exposure (80 mg L(-1)) enhanced malondialdehyde content (239%-427%), reactive carbonyl groups (425%-512%) and H2O2 (129%-294%) accumulation during 3-24 h of treatment, thereby indicating cellular peroxidation and oxidative damage. The quantitative estimations were in accordance with in situ detection of ROS generation (using 2',7'-dichlorodihydrofluorescein diacetate dye) and H2O2 accumulation. Pb2+ treatment significantly reduced ascorbate and glutathione content during 3-24 h of exposure. On the contrary, levels of non-protein thiols were enhanced by 3-11.8 time over control in response to 16-80 mg L(-1) Pb2+ treatment, after 24 h. A dose-dependent induction in ascorbate peroxidase and lipoxygenase enzyme activity was observed in Z. mays roots. The activities of ascorbate-recycling enzymes (dehydroascorbate reductase and monodehydroascorbate reductase) were significantly increased in relation to concentration and duration of Pb2+ treatment. The study concludes that Pb2+-exposure induces ROS-mediated oxidative damage during early period of exposure despite the upregulation of enzymes of ascorbate-glutathione cycle.