Accumulation of loganin and secologanin in vacuoles from suspension cultured Catharanthus roseus cells

The distribution of the iridoids loganin and secologanin at the subcellular level was studied in secologanin accumulating Catharanthus roseus cells. Vacuoles were isolated from protoplasts by an osmotic shock treatment, followed by flotation centrifugation. The iridoid and alkaloid 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. Utilizing these strategies we attempted to substantiate the possible vacuolar conversion of loganin to secologanin. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.