CHEMICAL COMPOSITION OF THE CELL WALLS OF THE FRESHWATER RED ALGA LEMANEA ANNULATA (BATRACHOSPERMALES)

Cell walls of the generic phase of the freshwater red alga Lemanea annulata Kütz were mechanically isolated and chemically characterized. Walls consisted mainly of polysaccharide with lesser quantities of associated protein and lipid. The major wall component was alkali‐soluble xylan, comprised mainly of 4‐linked β‐xylopyranosyl residues and small amounts of 3‐O‐substituted β‐xylopyranosyl residues. Hot water extracts yielded non‐sulfated polymers, with 3‐ or 3,4‐linked β‐galactosyl residues alternating with 4‐linked α‐glucuronosyl residues as the predominant structural features. This acid polysaccharide shares many characteristics of the mucilage previously described from the freshwater genus Batrachospermum. Isolated cell walls of L. annulata contained approximately 6% cellulose. Cellobiohydrolase/colloidal gold labelling of cell walls revealed β‐4‐glycan throughout the fibrillar portion of the wall. Wall protein consisted of at least 17 amino acids, of which threonine and alanine were the most abundant. Polysaccharides of the cell walls of L. annulata differ from those of marine red algae and are similar to those described for other Batrachospermales.