Elicitor Signaling Molecules In The Process Of Plant Defense Responses

Endogenous elicitor activity, termed CDW, was prepared from the cell walls of suspension-cultured ginseng (Panax ginseng C.A. Meyer) cells via cellulase degradation. CDW activated in vitro the NADPH oxidase activity of isolated plasma membranes and stimulated in vivo H2O2 generation by ginseng cell suspensions. CDW also increased the activity of phenylalanine ammonia lyase (PAL), expression of a P. ginseng squalene epoxidase (sqe) gene and saponin synthesis. NADPH oxidase inhibitors inhibited both in vitro NADPH oxidase activity and in vivo H2O2 generation. Induction of PAL activity, saponin synthesis and sqe gene expression were all inhibited by such inhibitor treatments and reduced by incubation with catalase and H2O2 scavengers. These data indicate that activation of NADPH oxidase and generation of H2O2 are essential signalling events mediating defence responses induced by the endogenous elicitor(s) present in CDW.