Regulation of elicitin-induced ethylene production in suspension-cultured tobacco BY-2 cells

INF1 elicitin, a proteinaceous elicitor produced by Phytophthora infestans, induces a hypersensitive response in tobacco BY-2 cells. In response to elicitin, tobacco cells produce both reactive oxygen species (ROS) and ethylene (ET). To investigate the regulation of elicitin-induced ET production, we pharmacologically analyzed the effects of several chemicals on ET production. Inhibitors of ROS generation or ROS chelators efficiently inhibited ET production, whereas simultaneous treatment of a superoxide anion-generating system with salicylhydroxamic acid recovered ET production. In an in vitro experiment, superoxide anion was necessary and sufficient for conversion of 1-aminocyclopropane-1-carboxylate (ACC) to ET because ET was produced from ACC solely in the presence of the superoxide-generating chemical KO₂. ET production was also inhibited by lipoxygenase (LOX) inhibitors, indicating a possible involvement of LOX-mediated generation of superoxide anion and ET production itself. Furthermore, elicitin-induced ET production was completely inhibited by the protein synthesis inhibitor cycloheximide but recovered after exogenous application of ACC, indicating that de novo protein synthesis is required for ACC accumulation, leading to ET production. We also investigated the effects of several phytohormones on elicitor-induced ET production and discuss their role in the defense response.