Phospholipase D involvement in the plant oxidative burst

Pathogen-triggered generation of reactive oxidants, termed the oxidative burst, contributes to disease resistance in both plant and animal kingdoms. Since phospholipase D plays a key role in the neutrophil oxidative burst signaling cascade and is highly abundant in plants, we investigated its participation in the plant oxidative burst. Thin layer chromatography of extracted phospholipids revealed no changes in phosphatidic acid levels in soybean cells undergoing oxidant production, and no changes in phosphatidyl-ethanol biosynthesis could be detected when ethanol was present during elicitation. An inhibitor of phosphatidic acid hydrolase, propranolol, did not modify burst parameters or phosphatidic acid levels during the burst, suggesting our inability to detect phosphatidic acid accumulation was not due to rapid elimination. Furthermore, exogenous phosphatidic acid did not elicit a burst or enhance elicitor-stimulated bursts. Finally, ethanol, a substitute nucleophile, did not abrogate the burst. With data showing the presence of phospholipase D in soybean cells, these data argue that soybean phospholipase D does not participate in signaling the oxidative burst. This constitutes the first major difference between the plant and animal oxidative burst signal transduction pathways.