INFLUENCE OF PRECURSOR AVAILABILITY ON ALKALOID ACCUMULATION BY TRANSGENIC CELL-LINE OF CATHARANTHUS-ROSEUS

We have used a transgenic cell line of Catharanthus roseus (L.) C. Don to study the relative importance of the supply of biosynthetic precur sors for the synthesis of terpenoid indole alkaloids. Line S10 carries a recombinant, constitutively overexpressed version of the endogenous strictosidine synthase (Str) gene. Various concentrations and combina tions of the substrate tryptamine and of loganin, the immediate precur sor of secologanin, were added to suspension cultures of S10. Our resu lts indicate that high rates of tryptamine synthesis can take place un der conditions of low tryptophan decarboxylase activity, and that high rates of strictosidine synthesis are possible in the presence of a sm all tryptamine pool. It appears that the utilization of tryptamine for alkaloid biosynthesis enhances metabolic flux through the indole path way. However, a deficiency in the supply of either the iridoid or the indole precursor can limit flux through the step catalyzed by strictos idine synthase. Precursor utilization for the synthesis of strictosidi ne depends on the availability of the cosubstrate; the relative abunda nce of these precursors is a cell-line-specific trait that reflects th e metabolic status of the cultures.