PLASMA-MEMBRANE REDOX ENZYME IS INVOLVED IN THE SYNTHESIS OF O2- AND H2O2 BY PHYTOPHTHORA ELICITOR-STIMULATED ROSE CELLS

An elicitor prepared from the autoclaved cell walls of Phytophthora sp. induced O-2(-) generation and H2O2 accumulation by cultured cells of Rosa damascena Mill. cv Gloire de Guilan. N,N-Diethyldithiocarbamate, a superoxide dismutase inhibitor, blocked H2O2 accumulation and caused a dramatic accumulation of O-2(-) by elicitor-treated rose cells. In the absence of N,N-diethyldithiocarbamate no detectable O-2(-) was accumulated. Diphenyleneiodonium, quinacrine, pyridine, and imidazole, inhibitors of the mammalian neutrophil NADPH oxidase responsible for the generation of O-2(-) during phagocytosis, inhibited O-2(-) generation by elicitor-treated rose cells. Diphenyleneiodonium also inhibited NADH-dependent O-2(-) production by plasma membranes isolated from rose cells. None of the four compounds inhibited the peroxidase activity in the cell-suspension medium. These results demonstrate that elicitor-stimulated accumulation of H2O2 comes only from superoxide dismutase-catalyzed dismutation of O-2(-). The data are inconsistent with the hypothesis that the synthesis of O-2(-) is catalyzed by extracellular peroxidase and suggest that the enzyme responsible for the synthesis of O-2(-) by elicitor-treated rose cells might be similar to the mammalian neutrophil NADPH oxidase.