Structural studies on the polysaccharides of the green seaweed Urospora wormskioldii and of the brown seaweeds Desmarestia ligulata and D. firma

Abstract

From investigations of two life stages of the green seaweed Urospora wormskioldii (U. wormskioldii and Codiolum pusilium) it was found that both weeds synthesise the following ethanol soluble carbohydrates: glucose, fructose, sucrose, myo-inositol, glycericacid and a number of glucose containing oligosaccharides. Both weeds also synthesise starches comprising amylose and amylopectin as well as highly branched 1,3-linked glucans. Evidence for a1.4-linked homoxylan with C-2 branch points was found in U. wormskioldii and indications of a homoxylan both 1,3- and 1,4-linked was found in Codiolum. Small amounts of an a-1,3-linked mannan and large amounts of a B-1,4-linked mannan branched at C-6 and sulphated at C-2 were found in Codiolum, although U.wormskioldii contained only trace quantities of a mannan. Polydisperse heteropolysaccharides ("rhamnans") containing L-rhamnose, D-xylose and D-glucuronic acid and half ester sulphate linked to the rhamnose were found in both weeds. The glucuronic acid was found to be 1,4linked and end group and the xylose to be 1,4-linked and end group and in U. wormskioldii it was also 1,2,4-linked. The rhamnose residues were mainly 1,3-linked and sulphated at C-2 or C-4 and to a lesser extent 1,4-linked with sulphate groups at C-2 or C-3. A small amount of 1,2-linked and end group rhamnose units was also found. The "rhamnans" metabolised by Codiolum appear to be basically linear while those from U. wormskioldii appear to be highly branched with possibly 1,3,4- or 1,2,4-linked rhamnose branch points.The structural cell-wall polysaccharide in both weeds was found to be cellulose admixed with protein and "rhamnan". A "rhamnan" from the green seaweed Ulva lactuca was found to be a linear polysaccharide consisting of 1,4- (major), 1,3-linked and end group rhamnose, 1,4-linked xylose and 1,4-linked and end group glucuronic acid. The "fucans" (polydisperse heteropolysaccharides) from the brown seaweeds Himanthalia lorea and Padina pavonia were found to consist of fucose, glucuronic acid, xylose and traces of galactose (H. lorea). The xylose and glucuronic acid were found to be1,4-linked and end group while the fucose was found to be 1,3-linked with sulphate groups at C-2 or C-4 and 1,4-linked with sulphate groups at C-3. Indications were obtained for a linear fucose backbone for these "fucans". The two brown seaweeds Desmarestia ligulata and Desmarestia firma were both found to have a high content of free sulphuric acid in the vacuolar sap. The free sulphuric acid in D. firma was found to be 6% of the dry weight of the weed. Consequently new methods to avoid degradation of the polysaccharides had to be devised. Both weeds were found to synthesise inannitol as their main ethanol soluble material though oligosaccharides containing xylose and galactose (D. firma) and xylose, galactose and mannose (D. ligulata) as well as myo-inositol (D. ligulata) and indications of glucose-mannitol di- and trimers (D. firma) were also found in this extract. Both weeds were found to synthesise laminaran, D. firma in comparativelylarge amounts. The "fucans" extracted from the two species were found to contain fucose, xylose, galactose, and glucuronic acid and mannose was also found in the "fucans" from D. ligulata. The alginic acid from D. ligulata was found to contain 33% of mannuronic acid and the mannuronic acid in both alginic acids was found to be more easily degraded and hydrolysed than the guluronic acid. The structural polysaccharide in D. ligulata was found to be cellulose.