Sterol composition and synthesis in potato tuber discs in relation to glycoalkaloid synthesis

The synthesis of sterols and sterol precursors was analysed in potato tuber discs, which accumulate glycoalkaloids, and in discs where this accumulation was inhibited by the addition of ethephon or tridemorph. In the 4,4-dimethylsterol fraction and the 4 alpha-methylsterol fraction, only compounds with a nonalkylated side-chain were found. The 4-desmethylsterols synthesized de novo were, in tridemorph-treated discs, pollinastanol and 5 alpha-cholest-8-en-3 beta-ol; in ethephon-treated discs, isofucosterol; and in control discs, isofucosterol and cholesterol. The cholesterol concentration decreased concurrently with the accumulation of glycoalkaloids. The results show that cholesterol synthesis is stimulated in potato discs and indicate that cholesterol is a precursor of glycoalkaloids in potato.