THE OSMOTIC SIGNIFICANCE OF THE HETEROSIDE FLORIDOSIDE IN THE MANGROVE ALGA CATENELLA-NIPAE (RHODOPHYTA, GIGARTINALES) IN EASTERN AUSTRALIA

The effect of salinity on the intracellular floridoside concentration in the mangrove alga Catenella nipae (Rhodophyta: Gigartinales) was investigated using C-13 nuclear magnetic resonance spectroscopy (C-13-NMR), and gas-liquid and high pressure liquid chromatography (GLC, HPLC). The floridoside content increased linearly with increasing salinity, and hence is strongly involved in osmotic acclimation in this species. In addition, during C-13-NMR analysis isethionic acid was identified as a new metabolite in C. nipae. The concentration of this compound also varied as a function of salinity. The steady-state contents of floridoside were also recorded in various geographically isolated field populations of C. nipae from mangroves along New South Wales coastline of Australia. All isolates contained very high floridoside levels. From these data, together with the physiological capability to accumulate floridoside under hypersaline conditions for osmotic acclimation, it is interpreted that floridoside is essential for survival in the extreme mangrove habitat.