Effects of copper on antixoidant enzyme activities, antioxidant and non-protein thiol content in Pontederia cordata’s leaves

Plants were cultivated in 50% Hoagland’s nutrient solution containing various concentrations of copper (i.e. 0, 5, 10 and 20 mg·L^–1) to experimentally characterize the copper tolerance and detoxification mechanism of Pontederia cordata. Changes in antioxidant enzyme activities, and non-protien antioxidant and thiol content in P. cordata’s leaves were analyzed to determine the redox state regulatory activities of leaves under copper treatment. The results showed that the malondialdehyde (MDA) content in leaves increased under copper stress. Superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR) activities first increased, and then decreased. Peroxidase (POD) and dehydroascorbate reductase (DHAR) activities increased, and catalase (CAT) activity decreased significantly with the expanded treatment time (P < 0.05). Accumulation of ascorbic acid (AsA) in leaves could be induced in early stages of copper treatment. Low concentration copper treatment (≤ 10 mg·L^–1) had no significant effect on the dehydroascorbic acid (DHA) content (P > 0.05). Among the total non-protein thiol (NPT) contents, glutathione (GSH) significantly increased with expanded treatment time . The phytochelatins (PCs) first increased and then decreased. Low concentration (≤ 10 mg·L^–1) and short-time copper treatment can enhance redox state regulatory activity in P. cordata leaves, improve the ability of cells to resist oxidative stress, and enhance the tolerance of plants to copper treatment. However, this stimulating effect is destroyed by higher concentrations, and longer copper treatment.