Abstract: The phytotoxicity and antioxidative adaptations of Pb accumulating ecotype (AE) and non-accumulating ecotype (NAE) of Sedum alfredii Hance were investigated under different Pb treatments involving 0, 0.02 mmol/L Pb, 0.1 mmol/L Pb and 0.1 mmol/L Pb/0.1 mmol/L EDTA for 6 days. With the increasing Pb level, the Pb concentration in the shoots of AE plants enhanced accordingly, and EDTA supply helped 51% Pb translocation to shoots of AE compared with those treated with 0.1 mmol/L Pb alone. Moreover, the presence of EDTA alleviated Pb phytotoxicity through changes in plant biomass, root morphology and chlorophyll contents. Lead toxicity induced hydrogen peroxide (H2O2) accumulation and lipid peroxidation in both ecotypes of S. alfredii. The activities of superoxide dismutase (SOD)， guaiacol peroxidase (G-POD,), ascorbate peroxidase (APX), and dehydroascorbate reductase (DHAR) elevated in both leaves and roots of AE as well as in leaves of NAE with the increasing Pb levels, but SOD and G-POD declined in roots of NAE. Enhancement in glutathione reductase (GR) activity was only detected in roots of NAE while a depression in catalase (CAT) activity was recorded in leaves of NAE. A significant enhancement in GSH and AsA levels occurred in both ecotypes exposed to Pb and Pb/EDTA treatment compared with CK, however, the difference between this two treatments were insignificant. The dehydroascorbate (DHA) contents in roots of both ecotypes were 1.41 to 11.22-folds higher than those in leaves, whereas the ratios of AsA to DHA (1.38 to 6.84) in leaves altering more to the reduced AsA form were much higher than those in roots. These results suggested that antioxidative enzymes and antioxidants played an important role in counteracting Pb stress in S. alfredii.

Key words: Antioxidant, Detoxification, EDTA, Phytoremediation, Sedum alfredii