The Effects of Salinity upon Galactosyl-Glycerol Content and Concentration of the Marine Red Alga Porphyra purpurea (Roth) C.Ag.

Abstract

Changes in the major alcohol-soluble, low molecular weight carbohydrates of <it>P. purpurea</it>, <it>O</it>-α-D-galactopyranosyl-(1-→2)-glycerol (‘floridoside’) and <it>O</it>-α-D-galactopyranosyl-(1-→1)-glycerol (‘isofloridoside’), have been examined in response to salinity variation. ‘Floridoside’ is shown to vary in absolute amount, increasing in hypersaline and decreasing in hyposaline media. ‘Isofloridoside’ content per cell does not change in a similar manner. Responses are almost identical under light or dark conditions, ‘floridoside’ changes being complete within 24 h. Decreasing the external water potential using ionic and non-ionic solutes has the same effect upon galactosyl-glycerol content. The amount of ‘floridoside’ synthesized, and degraded under hypersaline and hyposaline conditions respectively is shown to be insufficient to restore cell volume to its original value. It is therefore suggested that the primary function of ‘floridoside’ increases in concentrated sea-waters is that of a compatible solute, serving to protect the cell during periods when the external salt content is increased dramatically.