Intracellular distribution of the hydrophobic triterpene, bryonolic acid, in cultured cells of Luffa cylindrica L.

Intracellular localization of bryonolic acid, an antiallergic pentacyclic triterpene, in cultured cells of Luffa cylindrica was investigated with reference to the sites of its biosynthesis and accumulation. The results of cell fractionation showed that bryonolic acid was mostly located in the cell wall fraction. The addition of FC-43 emulsion to the culture medium was found to cause the release of bryonolic acid from the cell wall into the medium without affecting cell growth and bryonolic acid production. Under this culture condition, (14)C-labeled sodium acetate administered to the cells was rapidly incorporated into bryonolic acid which was then excreted into the medium within 10 min after administration. Electron microscopic observations suggested that spherical vesicles (ca 0.1 μm in diameter) derived from the rough endoplasmic reticulum may be associated with the biosynthesis and excretion of this compound into the cell wall. Furthermore, the activity of 2,3-oxidosqualene cyclase, a key enzyme involved in the biosynthesis of bryonolic acid, was detected in the microsomal fraction containing the endoplasmic reticulum.