Cadmium treatment enhances the production of alkaloid secondary metabolites in Catharanthus roseus

We investigated the effect of cadmium (Cd) on the yield of ajmalicine, a secondary metabolite derived from tryptophan, in the suspension cultures of a fully habituated cell line of Catharanthus roseus. The treatment with Cd concentration ranging from 0.05 to 0.4 mM and the duration of 24 to 48 h increased ajmalicine production and excretion into culture medium, particularly for cells at the mid-exponential growth phase. For early stationary phase cells and stationary phase cells transferred from the culturing medium to the production medium, we detected less enhancement. Cd treatment in cells at the mid-exponential phase, early stationary phase, and cells transferred from the growth medium to production medium increased the cellular content of tryptophan and tryptamine, the precursors for ajmalicine. The tryptamine level was a major limiting factor for ajmalicine production for cells at the mid-exponential phase. The tryptophan decarboxylase (TDC) converting tryptophan to tryptamine was also affected by Cd. We demonstrated that Cd treatment increased the level of TDC transcript, the cellular tryptamine concentration, and ajmalicine excretion, all contributed to the higher yield of ajmalicine. The increase was more significant in cells with active metabolic status and the cellular tryptamine concentration was the major limiting factor for ajmalicine biosynthesis. (C) 2003 Elsevier Ireland Ltd. All rights reserved.