Phosphatidylcholine, labeled by two fluorescent fatty acids, was fed to cultured plant cells (Petrosilenum crispum, L.; VBI-0, Nicotiana benthiana, L.) and fluorescent diacylglycerol (DAG) was the major metabolite. When a glycoprotein elicitor, derived from Phytophthora sojae, was applied to the parsley cells and the small protein cryptogein from Phytophthora cryptogea was applied to the tobacco cells. these signal substances strongly and rapidly decreased the pool of fluorescent diacylglycerol and weakly increased the pool of free fluorescent fatty acid and of fluorescent lysophosphatidylcholine. The cells responded in a very similar way to the application of mastoparan, a wasp venom peptide. As phosphatidic acid was only a very minor fluorescent metabolite DAG is hypothesized to arise by the action of a phosphatidylcholine-hydrolyzing phospholipase C which was down-regulated by elicitors. Up-regulation of a phospholipase A by elicitors is also suggested by these results. This is the first evidence for phosphatidylcholine-hydrolyzing phospholipase C in plant signal transduction. (C) 2002 Elsevier Science (USA). All rights reserved.