REACTIVE OXYGEN INTERMEDIATES MEDIATE A SYSTEMIC SIGNAL NETWORK IN THE ESTABLISHMENT OF PLANT IMMUNITY

Recognition of an avirulent pathogen stimulates an oxidative burst gen erating O-2(-) and H2O2, and these reactive oxygen intermediates (ROIs ) cue the induction of defense genes and cell death in the development of a restricted lesion. This localized hypersensitive response (HR) i s accompanied by the development of systemic acquired resistance to vi rulent pathogens. Here we show that inoculation of Arabidopsis leaves with avirulent Pseudomonas syringae induces secondary oxidative bursts in discrete cells in distant tissues, leading to low-frequency system ic micro-HRs. The primary oxidative burst induces these systemic respo nses, and both the primary burst and the secondary microbursts are req uired for systemic immunity. Hence, ROIs mediate a reiterative signal network underlying systemic as well as local resistance responses.