Suppression of red light-induced resistance in broad beans to Botrytis cinerea by salicylic acid

We investigated the effect of salicylic acid (SA) on red light-induced resistance in broad beans to Botrytis cinerea. Both lesion formation and fungal development were suppressed on broad bean leaves kept under red light, producing anti-fungal compound(s). However, SA pre-treatment inhibited expression of red light-induced resistance dose-dependently, generating hydrogen peroxide (H2O2). Red light-induced resistance was recovered in the presence of a H2O2 scavenger, ascorbic acid or a NADPH oxidase inhibitor, diphenylene iodonium even in SA-pre-treated broad bean leaves. These results suggest that breakdown of red light-induced resistance in broad beans to B. cinerea is induced by membrane-mediated H2O2 generation. On the other hand, catalase activity in broad bean leaves was significantly enhanced under red light, but not in those pre-treated with SA and aminotriazole. We hypothesize that enhanced antioxidant enzyme catalase activity contributes to the inhibition of cell death in broad beans scavenging endogenous H2O2 generated by B. cinerea infection and to elicitor-dependent production of anti-fungal component(s) by living host cells; as a consequence, red light-induced resistance may be established. It is possible that an SA-dependent signaling pathway in broad beans is playing different roles in the plant-pathogen pathosystem.