Characterization of the Oligogalacturonide - lnduced Oxidative Burst in Cultured Soybean ( G / ycine max ) Cells ' Laurent Legendre

The rapid release of HzOz by elicited plant cells, recently termed the oxidative burst, was investigated in suspension-cultured soybean (Glycine max Merr. cv Kent) cells stimulated with a purified polygalacturonic acid (PCA) elicitor. Examination of the elicited cells by fluorescence microscopy revealed that virtually every living cell participates in the elicitor-induced H202 burst. Measurement of the kinetics of the response using a macroscopic fluorescencebased assay indicated that approximately 100 molecules of HzOz are generated per PCA molecule added, achieving a cumulative HzOz concentration of approximately 1.2 mmol L-' of packed cells. At the height of the defense response, 3 x 10-14 mo1 of H z 0 2 cell-' min-' are produced, a value comparable to the rate of HzOz production by myeloid cells of mammals. Variables affecting the rate and magnitude of the soybean oxidative burst were found to be mechanical stress, extracellular pH, and cell age. l h e PCAinduced oxidative burst was shown to undergo both homologous and heterologous desensitization, a characteristic of signal transduction pathways in animals. Homologous desensitization was obtained with PCA, and heterologous desensitization was observed with the C protein activator mastoparan, consistent with earlier observations showing that C proteins perform a regulatory function in this pathway. Finally, a model describing the possible role of the PCA-induced oxidative burst in the overall scheme of plant defense i s proposed.