Cross-protection of pepper plants stressed by copper against a vascular pathogen is accompanied by the induction of a defence response

Pepper (Capsicum annuum L.) plants stressed by copper showed less disease symptoms after inoculation with Verticillium dahliae Kleb. We tested if such protection was accompanied of a defence response induced by copper stress by measurement of peroxidase and chitinase activity, phenolics and the expression of four genes related to plant defence. Peroxidase activity, but not chitinase, increased in roots, stem and leaves of copper-stressed plants. However, treating the plants with an ethylene perception inhibitor (MCP) before applying the copper stress, caused a synergic enhancement of both enzymes in stem and cotyledons. Phenolic compounds were also induced by copper but downregulated by MCP in stem. The expression of a peroxidase gene (CAPO1), a sesquiterpene cyclase gene (CASC1), a PR1 gene (CABPR1) and a β-1,3-glucanase (CABGLU) was highly upregulated by copper stress, but MCP neither suppresses nor enhances such an effect. Globally, copper stress causes an induction of defence mechanisms that may partially explain tolerance to Verticillium wilt.