Lead bioaccumulation potential of an aquatic macrophyte Najas indica are related to antioxidant system

Plants of Najas indica bioaccumulated significantly higher amounts of Pb (3554 mu g g(-1) dw) when, exposed to varying concentrations of Pb(NO3)(2). This also led to increased malondialdehyde (MDA), electrical conductivity (EC) and H2O2 content. In response to this, the activities of antioxidant enzymes such as Superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), catalase (CAT) and glutathione reductase (GR) were elevated along with the induction of various molecular antioxidants including GSH, cysteine, ascorbic acid and proline. Further, Pb exposed plants showed significantly increased cysteine synthase and glutathione-S-transferase activity. Visible symptoms of toxicity were evident at 50 mu M after 4d showing chlorosis and fragmentation of leaves with mucilaginous discharge. It seems that bioaccumulated Pb is efficiently tolerated by Najas plants through activation of antioxidant system and thiolic pathways which was evident by the increased biomass up to 10 mu M Pb. Therefore, it appears that due to metal tolerance characteristics with high concentration factor these plants can find use in phytoremediation of aquatic system highly contaminated by Pb. (C) 2009 Elsevier Ltd. All rights reserved.