Biosynthesis of agar polysaccharides in Gracilaria chilensis bird, McLachlan et Oliveira

The agar polysaccharides of the red seaweed Gracilaria chilensis Bird, McLachlan et Oliveira were labelled with the stable isotope 13C by pulse feeding NaH13CO3 to samples of the seaweed acclimatised to indoor culture. An analytical method based on chemical derivatisation and GCMS was used to detect and monitor incorporation of the label into the dynamic carbon pool and individual units of the agar polysaccharides. Concurrent formation of three out of the four major units (d-galactopyranose, l-galactopyranose 6-sulfate, and 6-O-methyl-d-galactopyranose) was observed in frond tips. Formation of the ring-closed 3,6-anhydro-l-galactopyranosyl residues from 6-O-sulfo-l-galactopyranosyl residues was considerably slower. Similar behaviour was observed in the segment of the frond adjacent to the tips. Floridean starch may be utilised for agar polysaccharide biosynthesis in the absence of light and CO2, when its level is high.