CHARACTERIZATION OF THE OLIGOGALACTURONIDE-INDUCED OXIDATIVE BURST INCULTURED SOYBEAN (GLYCINE-MAX) CELLS

The rapid release of H2O2 by elicited plant cells, recently termed the oxidative burst, was investigated in suspension-cultured soybean (Gly cine max Merr. cv Kent) cells stimulated with a purified polygalacturo nic acid (PGA) elicitor. Examination of the elicited cells by fluoresc ence microscopy revealed that virtually every living cell participates in the elicitor-induced H2O2 burst. Measurement of the kinetics of th e response using a macroscopic fluorescence-based assay indicated that approximately 100 molecules of H2O2 are generated per PGA molecule ad ded, achieving a cumulative H2O2 concentration of approximately 1.2 mm ol L-1 of packed cells. At the height of the defense response, 3 x 10( -14) mol of H2O2 cell-1 min-1 are produced, a value comparable to the rate of H2O2 production by myeloid cells of mammals. Variables affecti ng the rate and magnitude of the soybean oxidative burst were found to be mechanical stress, extracellular pH, and cell age. The PGA-induced oxidative burst was shown to undergo both homologous and heterologous desensitization, a characteristic of signal transduction pathways in animals. Homologous desensitization was obtained with PGA, and heterol ogous desensitization was observed with the G protein activator mastop aran, consistent with earlier observations showing that G proteins per form a regulatory function in this pathway. Finally, a model describin g the possible role of the PGA-induced oxidative burst in the overall scheme of plant defense is proposed.