GINKGOLIDE AND BILOBALIDE BIOSYNTHESIS IN GINKGO-BILOBA .2. IDENTIFICATION OF A POSSIBLE INTERMEDIATE COMPOUND BY USING INHIBITORS OF CYTOCHROME P-450-DEPENDENT OXYGENASES

The presence of diterpene hydrocarbons as biosynthetic intermediates i n the formation of ginkgolides and bilobalide has been investigated in Ginkgo biloba seedlings. Diterpene hydrocarbons are present only in r oots, as trace amounts (1-3 mu g g(-1) FW). Dehydroabietane is the mai n hydrocarbon compound. Two inhibitors of cytochrome P-450-dependent o xygenases, tetcyclacis and clotrimazole, were supplied to the seedling s via the roots in order to deregulate the terpene pathway. As a conse quence of the treatment with inhibitors, the ginkgolide and bilobalide content was lowered, both in roots and leaves. A treatment with 10 mM tetcyclacis was more effective than a 100 mM clotrimazole treatment a nd resulted in a strong increase (up to 41 times) of diterpene hydroca rbons in roots. This increase concerned primarily dehydroabietane. (CO 2)-C-14 feeding experiments, following 10 mu M tetcyclacis treatment, showed that only dehydroabietane was highly labelled. The absence of l abelling in both ginkgolides and bilobalide indicates that the oxygena tion reactions leading to the end-products are fully inhibited. All to gether, these results support the existence of a precursor-product rel ationship between dehydroabietane and ginkgolides plus bilobalides. Th e biosynthesis of oxygenated terpenes in G. biloba proceeds via a hydr ocarbon intermediate.