Tracer studies on the incorporation of [2-C-14]-DL-mevalonate into chlorophylls a and b, alpha-chaconine, and alpha-solanine of potato sprouts

Chlorophyll and glycoalkaloids are synthesized in different parts of the po tato plant including leaves, tubers, and sprouts. Although light stimulates the biosynthesis of both constituents, the question of whether the two bio synthetic pathways are under the same genetic control has not been resolved . This study investigated the dynamics of incorporation of labeled [2-C-14] -DL-mavalonate into chlorophyll a, chlorophyll b, and the glycoalkaloids a lpha -chaconine and alpha -solanine in potato sprouts after 7 and 14 days o f storage in the light and in the dark. No chlorophyll synthesis occurred i n the dark. Fractionation of the "glycoalkaloid" extract followed by high-p erformance liquid chromatography produced four peaks. The fractions were co llected and analyzed for radioactivity. About 80% of the radioactivity resi ded in fraction 1, the composition of which is unknown. Two of the fraction s, with 1-14% of the original label, were alpha -chaconine and alpha -solan ine. The radioactivity derived from mevalonate largely resides in unidentif ied compound(s) eluting as a single peak on the HPLC column before the peak s associated with the glycoalkaloids. The specific radioactivity of alpha - chaconine and a-solanine increased similar to2-fold in going from 7 to 14 d ays of exposure in the light and in the dark. These and additional observat ions point to the near identity of the dynamics of biosynthesis of the two glycoalkaloids. These data also implicate a non-mevalonate pathway for the synthesis of both chlorophylls and the glycoalkaloids and are consistent wi th independent genetic control of the concurrent formation of the two class es of compounds during greening of potatoes.