BIOSYNTHETIC ACTIVITY AND GALACTAN COMPOSITION IN DIFFERENT REGIONS OF THE THALLUS OF GRACILARIA-CHILENSIS BIRD, MCLACHLAN ET OLIVEIRA

Isotopic labelling with [C-13] and GC-MS analysis of the derived aldit ol acetates have been used to detect and investigate galactan biosynth esis in main branches and in four different regions along secondary br anches of the thallus of the red alga Gracilaria chilensis Bird, McLac hlan et Oliveira. Biosynthetic activity in terms of the proportion of new galactan produced within these regions decreases with increasing b ranch radius, i. e. with increasing distance from a branch tip, and is lower still in main branches. Gas-liquid chromatographic analysis of the alditol acetates of the constituent sugars of the galactan has sho wn that tissue age has little effect on the proportions of L-galactopy ranosyl-6-sulfate (i. e. precursor residues), or 6-O-methyl-D-galactop yranosyl residues in the galactan of this species.