Fungal elicitor-mediated responses in pine cell cultures : I. Induction of phenylpropanoid metabolism.

A tissue culture system has been developed to examine phenylpropanoid metabolism induced in pine tissues by an ectomycorrhizal symbiont. An elicitor preparation from the ectomycorrhizal fungus Thelephora terrestris Fr. induced enhanced phenolic metabolism in suspension cultured cells of Pinus banksiana Lamb., as indicated by tissue lignification and accumulation of specific methanol-extractable compounds in the cells. Induction of lignification was observed as early as 12 h after elicitation. The activity of phenylalanine ammonia-lyase (PAL, EC 4.3.1.5), the entry-point enzyme into phenylpropanoid metabolism, also increased within the same time-frame in elicited cells. Significant increases in PAL activity were evident by 6 h after elicitation, and, by 12 h after elicitation, PAL activity in elicited cells was ten times greater than that in the corresponding controls. Lignification of the elicited tissue was also accompanied by an increase in the activity of other enzymes associated with lignin synthesis, including caffeic acid O-methyl transferase (EC 2.1.1.46), hydroxycinnamate:CoA ligase (EC 6.2.1.12), cinnamyl alcohol dehydrogenase (EC 1.1.1.-), coniferin βglucosidase (EC 3.2.1.21) and peroxidase (EC 1.11.1.7). The increase in total peroxidase activity was associated with a change in the pattern of soluble peroxidase isoforms. The pine cell culture-ectomycorrhizal elicitor system provides a good model for molecular analysis of the process of lignification in an economically important softwood species.