[Effects of Cd2+ on antioxidant system in hepatopancreas of Procambarus clarkii]

By the method of toxicity bioassay, this paper studied the effects of different concentration (1.72, 3.44, 6.89, 13.77, and 27.55 mg x L(-1)) Cd2+ on the activities of antioxidative enzymes (SOD, CAT, and GSH-PX) and the antioxidation substances (GSH and Vc) in hepatopancreas of freshwater crayfish Procambarus clarkii. The results showed that the SOD activity was induced at the lowest concentration (1.72 mg x L(-1)) Cd2+ but inhibited at all other test concentrations Cd2+, and the inhibition degree was positively correlated with the Cd2+ concentration. Under all test concentrations Cd2+, the CAT activity decreased after an initial increase, with a peak 3 days after exposure. The CAT activity was sensitive to lower concentrations (< or = 6.89 mg x L(-1)) Cd2+, but had no significant difference at higher concentrations (>6.89 mg x L(-1)) Cd2+. When the Cd2+ concentration was < or = 6.89 mg x L(-1), the GSH-PX activity showed a trend of increasing first and then decreased; when the Cd2+ concentration was 13.77 or 27.55 mg x L(-1), the GSH-PX activity was depressed during the first day of exposure. When the Cd2+ concentration was < or = 6.89 mg x L(-1), the GSH content reached the highest value on the first day of exposure, and maintained at a higher level than the control group. However, when the Cd2+ concentration was > or = 13.77 mg x L(-1), the GSH content had no significant difference with the control. The Vc content was very sensitive to all test concentrations Cd2+. It decreased significantly on the first day of exposure, with the decrement positively correlated to Cd2+ concentration, but showed a recovering trend with exposure time. The results indicated that both the antioxidative enzymes and the antioxidation substances in the hepatopancreas of P. clarkii played important roles in coping with Cd2+ stress, and in most cases, showed a time- and dose-dependent relationship with Cd2+ concentration. The GSH-PX activity and Vc content of P. clarkii could be used as the potential bio-indicators in evaluating Cd2+ contamination.