Determination of metabolic rate-limitations by precursor feeding in Catharanthus roseus hairy root cultures

Precursors from the terpenoid and tryptophan branches were fed to Catharant hus roseus to determine which of the two branches limits metabolic flux to indole alkaloids. The feeding of tryptophan at 17 days of the culture cycle produced auxin-like effects. Addition of low levels of auxin or tryptophan resulted in significant increases in flux to the indole alkaloids. Convers ely, feeding higher levels of auxin or tryptophan resulted in increased bra nching and thickening of the hairy root cultures. A dramatic reduction in f lux to the alkaloids was also observed. However, feeding tryptamine or terp enoid precursors had no effect. Therefore, neither pathway tested revealed to be rate-limiting during the late growth phase. Feeding of either geranio l, 10-hydroxygeraniol, or loganin at 21 days each resulted in significant i ncreases in the accumulation of tabersonine. The addition of tryptophan or tryptamine had no effect during the stationary phase of the growth cycle. T hus, during the early stationary phase of growth the terpenoid pathway appe ars to be rate-limiting. Combined elicitation with jasmonic acid and feedin g either loganin or tryptamine did not further enhance the accumulation of indole alkaloids. (C) 2000 Elsevier Science B.V. All rights reserved.