Control and biological implications of alkaloid synthesis in Cinchona seedlings

Abstract

During germination of seeds of Cinchona ledgeriana, a rapid increase in alkaloid content occurs, which stops ca 4 days after the onset of germination. Cinchona alkaloids are derived from the precursor strictosidine, which itself is synthesized by enzymatic condensation of tryptamine and secologanin. When the increase in alkaloid content of the seedlings stops, both types of substrates and the necessary enzymatic activity for strictosidine synthesis are still present in the seedlings, suggesting that different intracellular compartmentation of these compounds prohibits further alkaloid biosynthesis. Indeed, upon homogenization and extraction in buffer of the seedlings, a pronounced increase in the amount of strictosidine was observed. External application of the alkaloids at concentrations higher than present in the seedlings showed autotoxic effects, which may explain why all substrate is not converted into alkaloid in the seedlings. At the concentration actually present in the seedlings, the alkaloids showed strong deterrence of feeding by slugs, indicating that this concentration is sufficient for ecological interactions. Moreover, the metabolic cost of carbon for alkaloid synthesis was estimated to be low.