CHEMICAL CHARACTERIZATION AND GELLING PROPERTIES OF CELL-WALL POLYSACCHARIDES FROM SPECIES OF ULVA (ULVALES, CHLOROPHYTA)

Two alkali-soluble polysaccharide fractions from the cell wall of Ulva 'rigida' were determined to be beta-1,4-linked glucoxylans and a beta -1,4-linked glucuronan by chemical and NMR spectroscopic analysis. The C-13 NMR spectrum of water-soluble xyloglucuronorhamnan sulfate from Ulva 'rigida' referred to as ulvan is reported and the C-13 and H-1 NM R chemical shifts of its major repeating unit, the aldobiuronic acid b eta-D-GlcA-(1,4)-L-Rha, are given. The composition and gelling propert ies of ulvan from Ulva species from 'green tides' are also reported. T he thermoreversible gel required both calcium and berate ions and the shear storage modulus G' was ion concentration dependent. The mechanis m of gelation and the associations of the different Ulva cell wall sol uble polysaccharides are discussed.