GINKGOLIDE AND BILOBALIDE BIOSYNTHESIS IN GINKGO-BILOBA .1. SITES OF SYNTHESIS, TRANSLOCATION AND ACCUMULATION OF GINKGOLIDES AND BILOBALIDE

Ginkgo biloba trees contain specific terpene compounds, ginkgolides (d iterpene) and bilobalide (pentanorditerpene). Ginkgolide A (GA) and gi nkgolide B (GB) are the main molecular forms of ginkgolides. These com pounds are present in young seedlings and accumulate within roots and leaves, but not in stems. In vitro experiments showed a correlation be tween accumulation of terpenes and rhizogenesis. Ginkgolides and bilob alide could easily be formed from (CO2)-C-14 when the photosynthesis c onditions were optimized. Ginkgolide A was first labelled, as early as 8 h after application of (CO2)-C-14. The ginkgolide labelling reached a maximum at day 3 followed by a steady state around day 10. Bilobali de labelling, occurred later and showed a maximum at day 6. The chrono logy of ginkgolide labelling indicated a possible in situ bioconversio n of ginkgolides from GA to GC, by successive additions of hydroxyl gr oup. With both (CO2)-C-14 and (U-C-14) glucose, the labelled terpenes were first detected in roots, and subsequently in stems and leaves. Th ese complementary experiments indicate that all the enzymic steps lead ing to the Ginkgo diterpene end products take place in the roots but n ot in the leaves. Ginkgo roots are, at the same time, a site of biosyn thesis and accumulation of ginkgolides and bilobalide, whereas leaves seem to act only as a sink. The balance of C-14-labelled terpenes in t he whole plant during the chase period (27 days) indicates that terpen es seem to be translocated from the roots to the leaves in a source-si nk manner. However, the possible involvement of modified terpene molec ules in the transport process as well as the localization of the trans location pathway are not known.