BIOSYNTHESIS OF AGAR POLYSACCHARIDES IN GRACILARIA-CHILENSIS BIRD, MCLACHLAN ET OLIVEIRA

The agar polysaccharides of the red seaweed Gracilaria chilensis Bird, McLachlan eh Oliveira were labelled with the stable isotope C-13 by p ulse feeding (NaHCO3)-C-13 to samples of the seaweed acclimatised to i ndoor culture, An analytical method based on chemical derivatisation a nd GCMS was used to detect and monitor incorporation of the label into the dynamic carbon pool and individual units of the agar polysacchari des, Concurrent formation of three out of the four major units (D-gala ctopyranose, L-galactopyranose 6-sulfate, and 6-O-methyl-D-galactopyra nose) was observed in frond tips. Formation of the ring-closed 3,6-anh ydro-L-galactopyranosyl residues from 6-O-sulfo-L-galactopyranosyl res idues was considerably slower. Similar behaviour was observed in the s egment of the frond adjacent to the tips, Floridean starch may be util ised for agar polysaccharide biosynthesis in the absence of light and CO2, when its level is high, (C) 1996 Elsevier Science Ltd.