Pb uptake and toxicity to Iris halophila tested on Pb mine tailing materials

Pb tolerant mechanisms, plant physiological response and Pb sub-cellular localization in the root cells of Iris halophila were studied in sand culture and the Pb mine tailings. Results showed that the activities of superoxide dismutase (SOD) and peroxidase (POD) in the underground parts and the activity of catalase (CAT) in the aboveground and underground parts increased as Pb level was enhanced. Glutathione (GSH) and ascorbic acid (AsA) contents increased by Pb treatments. Pb deposits were found in the middle cell walls or along the inner side of epibiotic protoplasm of some cells which accumulated a large quantity of Pb and died. The dry weights (DWs) of aboveground parts under all Pb tailings treatments decreased insignificantly, while the DW of the underground parts growing in the pure Pb tailings decreased significantly. Pb, Cu, Cd, and Zn contents increased significantly as the levels of Pb tailings were enhanced and Pb contents in the aboveground and underground parts reached 64.75 and 751.75 μg/g DW, respectively, at pure Pb tailings treatment. The results indicated that I. halophila is a promising plant in the phytoremediation of Pb contaminated environment. Some antioxidant enzymes, antioxidants and compartmentalization of Pb were played major roles in Pb tolerance of I. halophila.