In this study, the effect of multiple heavy metal stress on ascorbate (AsA), glutathione (GSH) and related enzymes was investigated in the leaves, stems and roots of Kandelia candel and Bruguiera gymnorrhiza. Mangrove seedlings were treated with five different concentrations of a heavy metal mixture (Cd2+, Pb2+ and Hg2+). Antioxidants in both the species were analyzed after one month. AsA, GSH, ascorbate peroxidase (APX, EC 1.11.1.11) and glutathione reductase (GR, EC 1.6.4.2) exhibited a similar trend with initial increase and subsequent decrease in response to heavy metal stress. At the highest metal concentration, a significant decrease of AsA and GR was observed in K. candel and B. gymnorrhiza. Glutathione peroxidase (GPX, EC 1.11.1.9) in the leaves, stems and roots of K. candel reached their respective maximal values at the highest metal concentration, whereas GPX activity in roots and stems of B. gymnorrhiza was similar to the controls at higher metal concentrations. Our results demonstrate that AsA, GSH, APX, GR and GPX in K. candel may play more important roles in defending against reactive oxygen species (ROS) than those in B. gymnorrhiza.
