[Effects of elevated Cd, Zn and their combined effects on antioxidant system of tobacco]

A solution culture was conducted to study the effects of elevated Cd and/or Zn ions (0.1 mmol·L^-1 Cd²⁺, 0.15 mmol·L^-1 Zn²⁺, 0.1 mmol·L^-1 Cd²⁺+0.15 mmol·L^-1Zn²⁺) on seed germination rate and reactive oxygen species (ROS) level, antioxidants contents, antioxidant enzyme activities and product of membrane lipid peroxidation in tobacco seedling leaves. The results showed that compared to control, the seed germination rate decreased under elevated level of Cd²⁺or Zn²⁺, the superoxide radical (O₂^-· ) generation rate and hydrogen peroxide (H₂O₂) content in tobacco seedlings increased, the activities of catalase (CAT), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDAR), and glutathione reductase (GR) increased, content of glutathione (GSH) and GSH/GSSG (oxidized glutathione) ratio decreased, and malondialdehyde (MDA) content increased. Compared to elevation of the level of only Cd²⁺ or Zn²⁺, the seed germination rate under elevation of both Cd²⁺ and Zn²⁺ levels was enhanced significantly; O₂^-· generation rate, contents of H₂O₂ and MDA decreased; CAT, APX and MDAR activities increased in the last stage of Cd²⁺ and Zn²⁺ exposure. Heavy metal Cd²⁺ or Zn²⁺ could induce the physiological injury to tobacco seedlings, and the toxic effects increased with prolonged stress time. The combined treatment of Cd and Zn could alleviate the toxicity of single stress on tobacco seedlings.