Ginkgolide and bilobalide biosynthesis in Ginkgo biloba. I : Sites of synthesis, translocation and accumulation of ginkgolides and bilobalide

Abstract

Ginkgo biloba trees contain specific terpene compounds, ginkgolides (diterpene) and bilobalide (pentanorditerpene). Ginkgolide A (GA) and ginkgolide B (GB) are the main molecular forms of ginkgolides. These compounds are present in young seedlings and accumulate within roots and leaves, but not in stems. In vitro experiments showed a correlation between accumulation of terpenes and rhizogenesis. Ginkgolides and bilobalide could easily be formed from 14 CO 2 when the photosynthesis conditions were optimized. Ginkgolide A was first labelled. as early as 8 h after application of 14 CO 2 . The ginkgolide labelling reached a maximum at day 3 followed by a steady state around day 10. Bilobalide labelling, occurred later and showed a maximum at day 6. The chronology of ginkgolide labelling indicated a possible in situ bioconversion of ginkgolides from GA to GC, by successive additions of hydroxyl group. With both 14 CO 2 and (U- 14 C) glucose, the labelled terpenes were first detected in roots. and subsequently in stems and leaves. These complementary experiments indicate that all the enzymic steps leading to the Ginkgo diterpene end products take place in the roots but not in the leaves. Ginkgo roots are, at the same time. a site of biosynthesis and accumulation of ginkgolides and bilobalide. whereas leaves seem to act only as a sink. The balance of 14 C-labelled terpenes in the whole plant during the chase period (27 days) indicates that terpenes seem to be translocated from the roots to the leaves in a source-sink manner. However, the possible involvement of modified terpene molecules in the transport process as well as the localization of the translocation pathway are not known.