Induction of plant phenolic amides by oligosaccharides

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A phenolic amide compound, p-coumaroyloctopamine (PCO), is induced in potato tuber disks by the treatment with beta-1,3-oligoglucosaccharide elicitor. The induction was observed in every potato cultivar collected in this study. Octopamine moiety of PCO was shown to be derived from tyrosine by the incorporation experiments using deuterium-labelled compounds. The level of free tyramine in the tuber tissue increased after the elicitor treatment, while no significant increase was observed regarding the octopamine level. Thus it was proposed that tyrosine is decarboxylated to tyramine, to which p-coumaroyl moiety is transferred from the corresponding CoA thioester, and the subsequent oxidation gives PCO in elicitor-treated potato tissue. The induction of PCO was thought to occur as a result of the activation of de novo synthesis caused by the oligosaccharide elicitor. The elicitor treatment coordinately raised the activities of tyrosine decarboxylase and tyramine hydroxycinnamoyl CoA transferase, the enzymes responsible for the formation of the octopamine moiety of PCO, together with those involved with phenylpropanoid metabolism including phenylalanine ammonia lyase and 4-hydroxycinnamic acid : CoA ligase. When the elicitor was applied in the presence of tiron or n-propyl gallate, the scavenger of active oxygen species, the induction of PCO was inhibited. The induction was also inhibited by diphenylene iodide, . an inhibitor of membrane-bound NADPH oxidase, suggesting that the active oxygen species produced by NADPH oxidase are involved with the signal transduction from the elicitor stimulation to the activation of PCO biosynthesis in potato tuber tissues.