Abstract
U18666A an inhibitor of 2,3-oxidosqualene: cycloartenol cyclase, was used to investigate whether elicitation of sesquiterpenoid phytoalexins in potato tuber discs by arachidonic acid alters the in vivo flow of substrate through 2,3-oxidosqualene. The level of 2,3-oxidosqualene increased 10-fold in potato tuber discs treated with a 10·0 μ m concentration of U18666A. The same concentration of U18666A inhibited steroid glycoalkaloid accumulation by 90%, but had no effect on the accumulation rishitin and lubimin elicited by arachidonic acid. In potato tuber discs treated with U18666A, 2,3-oxidosqualene accumulated to lower levels in arachidonic acid-elicited potato tuber discs than in non-elicited discs. The application of arachidonic acid also decreased the incorporation of radioactivity from [ 3H]mevalonate into squalene and 2,3-oxidosqualene in potato tuber discs treated with U18666A. These data provide evidence that suppression of squalene synthetase activity accounts, at least in part, for the reduction of sterol biosynthesis which occurs during the elicitation of sesquiterpenoid phytoalexin accumulation in potato tuber discs.
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