TEMPORAL CORRELATION OF TYRAMINE METABOLISM WITH ALKALOID AND AMIDE BIOSYNTHESIS IN ELICITED OPIUM POPPY CELL-CULTURES

Aromatic amines are involved in the biosynthesis of many plant seconda ry metabolites, including benzylisoquinoline alkaloids and hydroxycinn amic 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 tempor al 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 hy droxycinnamoyl 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 sa nguinarine and amides, respectively. In pulse-labeling experiments, a maximum of 1.2 and 0.6% of exogenous C-14-tyramine and C-14-dopamine, respectively, was incorporated into sanguinarine after elicitor treatm ent of cell cultures. In contrast, a maximum of 24 and 35% of exogenou s 14C-tyramine and C-14-dopamine, respectively, was incorporated into an acid-insoluble fraction of the cell wall after elicitor treatment. Insolubilized radioactivity was released from cell walls after hydroly tic extraction and recovered mostly as hydroxycinnamic acid amides and free amines. The elicitor-induced incorporation of C-14-amines into b oth sanguinarine and cell walls decreased during the cell culture grow th cycle. The prolonged induction of THT activity in elicited cultures , coupled with high and constitutive peroxidase activity, suggests tha t the observed decrease in cell wall labeling 5h after the addition of elicitor was due to hydroxycinnamoyl-CoA or H2O2 limitation. (C) 1998 Elsevier Science Ltd. All rights reserved.