Differential generation of hydrogen peroxide upon exposure to zinc and cadmium in the hyperaccumulating plant specie (Sedum alfredii Hance)

摘要

Sedum alfredii Hance has been identified as zinc (Zn) and cadmium (Cd) co-hyperaccumulator. In this paper the relationships of Zn or Cd hyperaccumulation to the generation and the role of H2O2 in Sedum alfredii H. were examined. The results show that Zn and Cd contents in the shoots of Sedum alfredii H. treated with 1000 μmol/L Zn²⁺ and/or 200 μmol/L Cd²⁺ increased linearly within 15 d. Contents of total S, glutathione (GSH) and H2O2 in shoots also increased within 15 d, and then decreased. Total S and GSH contents in shoots were higher under Cd²⁺ treatment than under Zn²⁺ treatment. However, reverse trends of H2O2 content in shoots were obtained, in which much higher H2O2 content was observed in Zn²⁺-treated shoots than in Cd²⁺-treated shoots. Similarly, the microscopic imaging of H2O2 accumulation in leaves using H2O2 probe technique showed that much higher H2O2 accumulation was observed in the Zn²⁺-treated leaf than in the Cd²⁺-treated one. These results suggest that there are different responses in the generation of H2O2 upon exposure to Zn²⁺ and Cd²⁺ for the hyperaccumulator Sedum alfredii H. And this is the first report that the generation of H₂O₂ may play an important role in Zn hyperaccumulation in the leaves. Our results also imply that GSH may play an important role in the detoxification of dissociated Zn/Cd and the generation of H₂O₂.