Localization of secologanin in Catharanthus roseus cells

The subcellular localization of the iridoids loganin and secologanin was studied in a secologanin accumulating Catharanthus roseus cell culture. Vacuoles were isolated from protoplasts by an osmotic shock treatment, followed by flotation centrifugation. The iridoid contents of cells, protoplasts and vacuoles were analysed by HPLC. Secologanin was found to be stored exclusively in the vacuoles. In loganin fed cells, loganin accumulated in the vacuoles while vacuolar secologanin contents increased, indicating that the conversion of loganin to secologanin occurs in the vacuoles. However, feedings of loganin to isolated protoplasts and vacuoles did not result in increased secologanin levels.