Abstract: The changes of chlorophyll content, antioxidant enzymes and osmotic regulations were investigated in two wheat seedlings, Xi Han and Ning Chun, treated with different concentrations of Pb(NO₃)₂. The results showed that there was no significant change of chlorophyll content and superoxide dismutase(SOD) activity in two wheat seedlings exposed to lower Pb(NO₃)₂ concentration, while the amount of chlorophyll a, chlorophyll b and total chlorophyll decreased and SOD activity significantly increased when wheat seedlings were subjected to higher Pb(NO₃)₂ concentration. The destroy to chlorophyll of Ning Chun was more serious than that of Xi Han in responses to the same Pb(NO₃)₂ stress. Different concentration of Pb(NO₃)₂ induced enhanced activities of catalase, peroxidase and ascorbate peroxidase, but no significant changes in malondialdehyde(MDA) content. In addition, the amount of proline increased by Pb(NO₃)₂ in two wheat seedlings in a concentrationdependent manner, but no change in soluble sugar content. The results suggested that chlorophyll content was destroyed and the activities of antioxidases and the amount of proline were enhanced in wheat seedlings under the stress of Pb(NO₃)₂, thus the stronger effects of antioxidanted role and osmotic regulations existed and enhanced wheat seedlings tolerance to Pb²⁺ stress. Therefore, there was no significant difference in MDA content between the control and Pb(NO₃)₂-stressed wheat seedlings.

Key words: Pb²⁺ stress, wheat, chlorophyll, antioxidant enzyme, proline