Abstract:In order to reveal the signaling pathways triggered by elicitor in plant microbe interactions, the mechanisms of hypersensitive necrosis responses in Nicotiana tabacum L. cv. Gexin Ⅲ induced by palmin were studied at molecular and cellular level. The burst of superoxide, intercellular diffusion of hydrogen peroxide and process of cell death induced by palmin were investigated in tobacco plants by biochemical methods and Confocal microscopy. The results showed that a large amount of O·[KG-*5]-2 was rapidly generated in tobacco cell elicited by palmin as a result of activation of NADPH oxidase, and the O·[KG-*5]-2 was dismutated into H2O2 immediately by superoxide dismutase (SOD). Accumulation and intercellular diffusion of H2O2 were shown to be a trigger for hypersensitive cell death; and Ca2+and some specific protein kinase were also shown to be involved in the activation of oxidative burst in tobacco cell induced by palmin.