MANNITOL IN THE RED ALGAL GENUS CALOGLOSSA (HARVEY) AGARDH,J.

Analytical data on the occurrence of the polyhydric alcohol mannitol in the red algal genus Caloglossa (Ceramiales, Delesseriaceae) were obtained by C-13 NMR and HPLC techniques. Six species were isolated in different geographic regions and kept in laboratory cultures. In all isolates intracellular mannitol concentrations ranging from 25.4 to 579.3 mmol kg-1 DW were measured. In field material of Caloglossa leprieurii from New South Wales, Australia the mannitol content appears to be influenced by salinity of the natural habitat: plants from freshwater (0 parts per thousand) contained 3.2 mmol kg-1 DW, plants from estuarine (26-35 parts per thousand) and marine (35 parts per thousand) habitats exhibited 40 and 202.6 mmol kg-1 DW respectively. Cultured material of Caloglossa apomeiotica was subjected to osmotic stresses ranging from 5.3 - 70 parts per thousand. The mannitol content linearly increased with increasing salinities. The possible function of mannitol as a compatible solute in Caloglossa is discussed. The occurrence of these high mannitol concentrations and the absence of typical red algal carbohydrates are discussed with reference to the chemotaxonomy of the genus.