Ultrastructure, chemical composition and biosynthesis of the cell wall in Koliella antarctica (Klebsormidiales, Chlorophyta)

The chemical composition, biosynthesis and ultrastructural organization of the cell wall of cultures of Koliella antarctica (Klebsormidiales, Chloroph yta), a green microalga obtained from samples of sea water taken near the I talian Station of Terra Nova (Ross Sea) during the austral summer 1989-1990 , have been studied. Purified cell walls of the microalga were sequentially treated with chemicals which, in higher plants, solubilize matrix polysacc harides (pectins and hemicelluloses) and leave an insoluble residue conside red to be alpha -cellulose. CDTA plus Na2CO3- and KOH-solubilized polysacch arides were made up of glucosyl residues (more than 90 mol%), as well as so me minor sugars (mannose and rhamnose). Linkage analysis and enzymic hydrol ysis of the matrix polysaccharides indicated the presence of beta -1,4-link ed glucans with minor amounts of other uncharacterized polysaccharides. The insoluble residue was composed of a small amount of crystalline alpha -cel lulose associated with mannan or glucomannan chains. The biosynthesis of ce ll wall polysaccharides was studied by incubating the microalgae in the pre sence of D-[U-C-14]glucose or myo-[U-C-14]inositol. The radioactive glycosy l residues incorporated into the polysaccharides solubilized from purified cell walls of the cultured microalga corresponded to those detected in the chemical analysis of the cell wall. The myo-inositol oxidation pathway was demonstrated to be functional in the microalga. Cell wall ultrastructural o bservations showed a loose network of cellulose microfibrils in an extended matrix.