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 p eroxide by the excretion of elicitors was investigated. Diffusate from spor es treated with H2O2 at a nonlethal concentration of 10-50 CIM induced necr otization of rice (Oryza sativa L.) callus and the excretion of fungitoxic metabolites by callus cells. Hydrogen peroxide in a higher (500 mu M) conce ntration 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 r eceptors.