Zusammenfassung
The production of H2O2 in soybean (Glycine max L. cv Harosoy 63) suspension cells upon treatment with a 1,3-1,6-beta-glucan elicitor fraction 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 synthesis in the cell culture. Production of H2O2 was measured by the in situ 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 ascorbate abolished the H2O2-mediated o-dianisidine oxidation. Diphenyleneiodonium, but not p-hydroxymercury benzoic acid, both known inhibitors of the mammalian NADPH oxidase involved in the oxidative burst of phagocytes, was a strong inhibitor of the inducible H2O2 production with a concentration for 50% inhibition of 4 mu M. The inhibitor studies also indicated that the oxidase might be at least in part responsible for H2O2 production by the cells. Furthermore, diphenyleneiodonium was the only inhibitor of O-2(-) synthesis in cell-free analyses with a concentration for 50% inhibition of 2.2 mu M. Neither ascorbate nor diphenyleneiodonium were able to inhibit elicitor-induced phytoalexin accumulation, indicating that in soybean H2O2 and O-2(-) may not be directly responsible for phytoalexin production, but may be an independent defence response. (C) 1997 Elsevier Science Ltd. All rights reserved.
