Matrix phase polysaccharides

4.2.1.2.1 (1^3,1^4)-$-d-GLUCANS

(1^3,1^4)-p-D-Glucans in seed plants (angiosperms and gymnosperms) are found ex­clusively in the walls of the grasses and certain related families (3, 17). Although the largest concentrations, up to 75%, of these polysaccharides occur in walls of the starchy endosperm of cereal grains such as barley (Hordeum vulgare) and oats (Avena sativa), they also occur, in lower concentrations in the primary walls of their vegetative organs (18, 19). For exam­ple, Smith and Harris (19) found 8.8% in primary walls from perennial ryegrass (Lolium perenne) stems.

The (1^3,1^4)-p-D-glucans are linear, unbranched polymers in which the (3-D-Glcp residues are joined by both (1^3)- and (1^4)-glucosidic linkages. Single (1^3)-linkages are separated by two or more (1^4)-linkages (Figure 4.1) and regions of two or three adjacent (1^4)-linkages predominate with longer (1^4)-p-D-glucosides (DP 5-14) ac­counting for <10% by weight of the molecules.