Effects of elicitation on different metabolic pathways in Catharanthus roseus (L) G. Don cell suspension cultures

Cell suspension cultures of Catharanthus roseus were elicited with an autoclaved cell-free filtrate of Pythium aphanidermatum. The regulation of alkaloid, terpenoid, and phenolic biosynthetic pathways was studied by product formation and assay of the enzyme activity of anthranilate synthase (AS), tryptophan decarboxylase (TDC), strictosidine synthase (SSS), strictosidine-beta-glucosidase (SG), isopentenyl diphosphate isomerase (IPP isomerase), geraniol-10-hydroxylase (G10H), chorismate mutase (CM), and phenylalanine ammonia lyase (PAL). After elicitation, AS and TDC activities were induced which resulted in an increase in the amount of tryptamine in the cells. For SSS and SG, no significant induction was observed. Ajmalicine accumulation was not increased compared with that in controls. An increased amount of phenolic compounds was found in the culture medium, although CM activity was not induced and PAL activity was inhibited after elicitor treatment. The activities of the enzymes IPP-isomerase and G10H were inhibited after elicitation. Also, the incorporation of [C-14]IPP in terpenoid products such as squalene was inhibited. These findings indicate a limitation in the terpenoid pathway which could promote a shortage of secoiridoid precursors for terpenoid indole alkaloid biosynthesis.