Abstract
The level of glycoalkaloids present in freshly cut potato tuber discs started to increase after 24 hours of incubation. This accumulation was inhibited by the sterol synthesis inhibitor, tridemorph, and was thus due to synthesis de novo. Concomitant to the accumulation of glycoalkaloids, there was an increase in the specific activity of a glycoalkaloid-specific enzyme, UDP-glucose:solanidine glucosyltransferase (solanidine-GT, EC 2.4.1). Time-course studies of enzyme activities in the discs showed that solanidine-GT activity increased at a low rate during the first 11 hours after slicing and at the highest rate between 11 and 16 hours. Other sterol-metabolizing enzymes exhibited different time-course curves:S-adenosyl-L-methionine:cycloartenol methyltransferase (cycloartenol-MT, EC 2.1.1.41) activity increased 5 hours after slicing and peaked at 11 hours. UDP-glucose:sterol glucosyltransferase (sterol-GT, EC 2.4.1) activity was not enhanced as a result of wounding. The accumulation of glycoalkaloids was not affected by light exposure or addition of abscisic acid, gibberellic acid or (2-chloroethyl)trimethylammonium chloride to the discs. Inhibition of ethylene synthesis or action gave a higher content of glycoalkaloids than in control discs, whereas discs incubated at high levels of ethylene had a very low glycoalkaloid content and also a lower activity of solanidine-GT than control discs.
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