Elicitor-induced defence responses of a suspension-cultured woody plant (Larix decidua) and possible mechanisms of signal transduction

Treatment of suspension-cultured larch cells (Larix decidua Mill.) with an elicitor derived from the cell wall of Fusarium oxysporum Schlecht. triggers very rapid defence responses like an oxidative burst and an increased calcium influx from the medium into the cell, all occurring within minutes after elicitation. These rapid responses are followed by a much slower set of changes like increased activities of phenylalanine ammonia-lyase and peroxidases and enhanced lignin biosynthesis. This paper describes both rapid and slow reactions of a cell culture derived from a woody plant to an elicitor from a facultative pathogen. Experiments concerning the transduction of the elicitor signal showed that the presence of calcium in the medium is indispensable for all elicitor responses of larch cells. It can be demonstrated that H2O2 is not a part of the signal chain. The importance of inositol phosphates and protein phosphorylation were studied using inhibitors. Neomycin, an inhibitor of the phosphoinositol pathway, blocked only the slower responses whereas staurosporine, an inhibitor of protein kinases, blocked both rapid and all the stower reactions. These results support the hypothesis that phosphorylation plays an important role even in very early stages of the signal transduction.