INVOLVEMENT OF AN NAD(P)H OXIDASE IN THE ELICITOR-INDUCIBLE OXIDATIVEBURST OF SOYBEAN

The production of H2O2 in soybean (Glycine max L. cv Harosoy 63) suspe nsion cells upon treatment with a 1,3-1,6-beta-glucan elicitor fractio n from the cell walls of Phyrophthora sojae was investigated. The beta -glucan elicitor used in these studies was specifically recognized by the soybean beta-glucan-binding proteins and induced phytoalexin synth esis in the cell culture. Production of H2O2 was measured by the in si tu oxidation of o-dianisidine and was both a time- and a concentration -dependent process, with a maximal response occurring after 20-25 min. Inhibitor studies showed that catalase, peroxidase inhibitors and asc orbate abolished the H2O2-mediated o-dianisidine oxidation. Diphenylen eiodonium, but not p-hydroxymercury benzoic acid, both known inhibitor s of the mammalian NADPH oxidase involved in the oxidative burst of ph agocytes, was a strong inhibitor of the inducible H2O2 production with a concentration for 50% inhibition of 4 mu M. The inhibitor studies a lso indicated that the oxidase might be at least in part responsible f or H2O2 production by the cells. Furthermore, diphenyleneiodonium was the only inhibitor of O-2(-) synthesis in cell-free analyses with a co ncentration for 50% inhibition of 2.2 mu M. Neither ascorbate nor diph enyleneiodonium were able to inhibit elicitor-induced phytoalexin accu mulation, indicating that in soybean H2O2 and O-2(-) may not be direct ly responsible for phytoalexin production, but may be an independent d efence response. (C) 1997 Elsevier Science Ltd. All rights reserved.