Possible involvement of active oxygen species in the double induction of plant defense responses

The ability of spores of Magnaporthe grisea fungus to respond to hydrogen peroxide by the excretion of elicitors was investigated. Diffusate from spores treated with H2O2 at a nonlethal concentration of 10-50 μM induced necrotization of rice (Oryza sativa L.) callus and the excretion of fungitoxic metabolites by callus cells. Hydrogen peroxide in a higher (500 μM) concentration was ineffective. It is supposed that H2O2 and other active oxygen species formed by the host plant before pathogen invasion favor the release of fungal elicitors, thus promoting elicitor interaction with host plant receptors.