Copper-induced oxidative stress in Alternanthera philoxeroides callus

The callus of Alternanthera philoxeroides, an emerging plant, was subjected to different concentrations of Cu2+ (0, 0.05, 0.1, 0.2, 0.6, 0.8, and 1 mM) for a period of 5 days and the contents of soluble protein and malondialdehyde (MDA), activities of superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), and guaiacol peroxidase (G-POD, EC 1.11.1.7), levels of reactive oxygen species (ROS, such as O2−∙ and H2O2) were determined. Treatment with 0.05 mM Cu2+ enhanced the content of soluble protein and reduced levels of O2−∙ and H2O2. As the Cu2+ concentration exceeded 0.1 mM, the content of soluble protein decreased greatly and the amounts of two polypeptides (apparent molecular weights 45 and 39 kDa, respectively) became visible in sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE); SOD activity was enhanced markedly owing to the accumulation of O2−∙, while POD and CAT activities increased alternately in response to increased H2O2 content. Because of the congenerous function of POD and CAT, the H2O2 content dropped to a low level finally. An interesting result was that the MDA content decreased with the increasing concentration of Cu2+. The results of this study indicated that antioxidant enzymes (SOD, POD, and CAT) protected A. philoxeroides callus against copper stress efficiently, especially for SOD. Whether there was another protective mechanism in A. philoxeroides callus or not requires further research. The critical value of copper on A. philoxeroides callus was 0.1 mM.