Wound-Induced Tyramine Hydroxycinnamoyl Transferase in Potato (Solanum tuberosum) Tuber discs

The enzyme tyramine hydroxycinnamoyl transferase (THT) was induced by wounding in potato tuber discs (Solanum tuberosum var. Bintje). THT activity was barely detectable in the intact tuber but increased dramatically during two days in the outermost cell layers of the excised discs. Thereafter the activity declined but the enzyme remained induced for at least one week. The induction of THT, which was detectable 3 to 4 hours after wounding, was completely blocked by cycloheximide. The main products formed in vivo were identified as amides of ferulic acid with tyramine or octopamine. The concentration of these amides increased upon wounding but only about 6 days after preparation of the tuber slices. Mild alkaline hydrolysis of the suberin-enriched cell wall residue purified from healed tuber discs released feruloyltyramine and feruloyloctopamine together with free tyramine and octopamine. Moreover exogenously supplied [14C]-feruloyltyramine was very rapidly integrated into the cell walls of the first layer of cells at the surface of wound healing tuber discs. Taken together our results suggest that the induction of THT and the integration of cinnamoyltyramines into cell walls could be part of the primary response of potato tuber tissues to wounding.