C-13 AND H-1-NMR STUDIES ON DIGENEASIDE IN THE RED ALGA CALOGLOSSA-LEPRIEURII - A REEVALUATION OF ITS OSMOTIC SIGNIFICANCE

The main organic solutes potentially involved in the osmotic acclimati on of the euryhaline red alga Caloglossa leprieurii (Ceramiales) were analysed and spectroscopically characterised using natural abundance C -13 and H-1 nuclear magnetic resonance (NMR) spectroscopy and gas-liqu id chromatography/mass spectrometry (GLC/MS). In a marine and a freshw ater isolate of C. leprieurii the polyhydric alcohol D-mannitol played an important role as osmolyte. The heteroside digeneaside (alpha-D-ma nnopyranosyl-(1-2)-glycerate) occurs in both populations, but its conc entration remained low and almost unchanged with increasing external o smotic pressures. In addition the quaternary ammonium compound trans-4 -hydroxyprolinebetaine was detected in marine isolates of C. leprieuri i only. As with digeneaside the intracellular content remained low and unaffected by salinity. While both metabolites are obviously not invo lved in the osmotic acclimation of C. leprieurii, their possible funct ion as compatible solutes is discussed.