Copper Ion Elicits Defense Response in Arabidopsis thaliana by Activating Salicylate- and Ethylene-Dependent Signaling Pathways

Dear Editor, Copper, one of the micronutrients, is essential during vegetative growth, development, and multiplication of plants （Penarrubia et al., 2010）. Copper is widely known for its application in fungicides and bactericides in agriculture since the late 19th century, for example, in the well-known Bordeaux mixture. Previous studies show that the mechanisms of copper ionsmediated antimicrobial activity involve either inhibition of the enzymes participated in fungal spore germination or direct toxicity on the growth of bacteria. Two studies also show that excessive copper is able to activate mitogen-activated protein （MAP） kinase signaling and upregulate defense-related genes in rice （Yeh et al., 2003; Sudo et al., 2008）. In addition, the application of copper was found to suppress the spread of Xanthornonas oryzae pv. oryzae PXO99A strain in rice （Yuan et al., 2010）. These previous studies imply that copper might be involved in regulating the defense response in plants.