Signalling molecules and the synthesis of alkaloids in Catharanthus roseus seedlings

The Madagascar periwinkle, Catharanthus resells, produces numerous alkaloids, several of which have important pharmaceutical uses. Catharanthus seedlings rapidly accumulate the monomeric alkaloids, vindoline, catharanthine and tabersonine, during germination. Various plant signalling molecules were tested for their ability to enhance alkaloid synthesis in Catharanthus seedlings. The compounds tested included plant hormones, fatty acid-derived messengers and agents that can induce systemic-acquired resistance in plants. Of these compounds, only methyl jasmonate (MeJa) enhanced the synthesis of monomeric alkaloids. However, feeding of a MeJa biosynthetic precursor, or inhibition of the lipoxygenase pathway, had no effect on alkaloid production in the seedlings. We conclude that, although MeJa is able to enhance alkaloid synthesis when supplied exogenously, the lipoxygenase pathway probably does not play a role in the regulation of alkaloid synthesis during normal germination of Catharanthus. Furthermore, it was found that Catharanthus seedlings accumulate small quantities of the dimeric alkaloid, vinblastine, a valuable antitumour drug. Contrary to its effect on the accumulation of monomeric alkaloids, MeJa did not influence the accumulation of vinblastine.