Copper-caused oxidative stress triggers the activation of antioxidant enzymes via ZmMPK3 in maize leaves

Copper (Cu) is a necessary trace element participated in many physiological processes in plants. But excessive Cu(2+) is toxic, which can activate intracellular signals that lead to cellular damage. The mitogen-activated protein kinase (MAPK) cascade is at the center of cell signal transduction and has been reported to be involved in stress-related signaling pathways. ZmMPK3, a kind of MAPKs in maize cells, can be activated by diverse abiotic stresses. In the present study, we investigated the effects of Cu(2+) on hydrogen peroxide (H(2)O(2)) level, ZmMPK3 activity as well as the activities of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and ascorbic acid peroxidase (APX) using maize leaf as an experimental model. The results demonstrated that acute Cu(2+) exposure for 24 hours led to rapid increases of H(2)O(2) level and the increase in ZmMPK3 activity as well as the total activities of antioxidant enzymes SOD, CAT and APX. H(2)O(2) scavenger, dimethylthiourea (DMTU), effectively inhibited the Cu(2+)-increased H(2)O(2) level and the activity of ZmMPK3 as well as the activities of the antioxidant enzymes SOD, CAT and APX. Pre-treatment with the MAPK inhibitor, PD98059, significantly blocked the Cu(2+)-increased activities of ZmMPK3, CAT, APX and SOD, but didn’t affect the accumulation of H(2)O(2). Our results suggest that Cu(2+) causes oxidative stress to the maize leaves which then activates defense antioxidant enzymes via MAPK pathway. Thus, the signaling pathway is Cu(2+)—H(2)O2—ZmMPK3—antioxidant enzymes.