Cell wall composition of the carrageenophyte Kappaphycus alvarezii (Gigartinales, Rhodophyta) partitioned by wet sieving

The cortical and medullary cells of Kappaphycus alvarezii fractions were screened by wet sieving after aqueous extraction of carrageenans. The cell populations obtained showed a clear partition between these two cell types. The main monosaccharide in hydro-insoluble cell walls was cellulosic glucose (70% dry weight), the crystallinity of which was shown to range from 20% in the cortical cells to 45% in the large medullary cells (over 250 mu m diameter). Minor monosaccharides in the insoluble fraction were galactose, 3,6-anhydrogalactose (indicating presence of residual carrageenans), mannose and xylose. However, the major part of the remaining galactose probably originated from another galactoglycan strongly linked to insoluble polymers in the large medullary cell walls. The mannose concentration was maximum in the cortical cells and decreased with increasing size of the medullary cells. Thus, besides cellulose, two other types of polysaccharides were detected in insoluble cell walls, mannoglycans and galactoglycans in cortical and medullary cell walls, respectively.