Abstract: Effects of different cadmium (Cd) concentrations (0, 1, 2 and 4 mmol·L^-1) on the seed germination, seedling growth and physiological property of Petunia hybrida were studied. In comparison with the control, seed germination and seeding growth exhibited a significant decrease at low level of Cd²⁺ concentration(1 mmol·L^-1), and these factors were all completely restrained at high concentration(4 mmol·L^-1). Compared to the control, the activities of peroxidase (POD) and catalase (CAT) were enhanced in P.hybrida seedings exposed to low Cd concentrations but inhibited at higher concentrations; the activities of ascorbate peroxidase (APX) and superoxide dismutase (SOD) could be increased in response to different Cd concentrations, no significant change in the malonaldehyde (MDA) content was observed. Ethylene-aminetetraacetic acid (EDTA) could stimulate the activities of POD and CAT in P.hybrida seedlings exposed to 4 mmol·L^-1 Cd treatment, and MDA content was also enhanced when seedlings were treated with 4 mmol·L^-1 Cd in the presence of 6 mmol·L^-1 EDTA. In conclusion, these results indicate that Cd stress significantly inhibit P.hybrida seed germination and seedling growth, but stimulate the activities of POD, CAT and APX in the leaves of seedlings; the application of EDTA further enhance the activities of POD and APX in Cd-treated P.hybrida seedlings. Therefore, higher activities of antioxidative enzymes may protect P.hybrida seedlings against Cd-induced oxidative change.

Key words: antioxidant enzymes, Petunia hybrida, Ethylene-aminetetraacetic acid, seed germination, cadmium stress