Temporal Correlation of Tyramine Metabolism with Alkaloid and Amide Biosynthesis in Elicited Opium Poppy Cell Cultures : In Honour of Professor G. H. Neil Towers 75th Birthday

Abstract

Aromatic amines are involved in the biosynthesis of many plant secondary metabolites, including benzylisoquinoline alkaloids and hydroxycinnamic acid amides. Incorporation of tyramine and dopamine into both the antibiotic alkaloid sanguinarine and hydroxycinnamic acid amides was shown to occur in elicitor-treated opium poppy cell cultures. A temporal correlation was demonstrated between the biosynthesis of alkaloids and amides, the accumulation of tyrosine\\dopa decarboxylase (TYDC) and berberine bridge enzyme (BBE) mRNAs, and the induction of tyramine hydroxycinnamoyl transferase (THT) activity. The induction of TYDC mRNAs occurred most rapidly, whereas the subsequent activation of BBE mRNAs and THT activity correlated with the synthesis and accumulation of sanguinarine and amides, respectively. In pulse-labeling experiments, a maximum of 1.2 and 0.6% of exogenous 14C-tyramine and 14C-dopamine, respectively, was incorporated into sanguinarine after elicitor treatment of cell cultures. In contrast, a maximum of 24 and 35% of exogenous 14C-tyramine and 14C-dopamine, respectively, was incorporated into an acid-insoluble fraction of the cell wall after elicitor treatment. Insolubilized radioactivity was released from cell walls after hydrolytic extraction and recovered mostly as hydroxycinnamic acid amides and free amines. The elicitor-induced incorporation of 14C-amines into both sanguinarine and cell walls decreased during the cell culture growth cycle. The prolonged induction of THT activity in elicited cultures, coupled with high and constitutive peroxidase activity, suggests that the observed decrease in cell wall labeling 5 h after the addition of elicitor was due to hydroxycinnamoyl-CoA or H2O2 limitation.