Xyloglucans from plant cell-walls structure

Figure 3. Segment of a plant cell wall (schematic drawing). Bundles of cellulose microfibers in near crystalline packing (thick bundles) are crosslinked by hemicelluloses (drawn as double-lined intercalated network) and pectins (fine lines with egg-box interaction sites). Carbohydrate-carbohydrate interaction occurs between individual cellulose chains, between cellulose and xyloglucan (a hemi-cellulose) and between different hemicelluloses and pectins. Besides different forms of non-covalent interactions (Ca + mediated egg-box structures as well as ion-independent forms of molecular interactions) also covalent ester linkages between carbohydrate chains are found (adapted from [23]).

From the results of cellulase digestion and the characterization of a number of oligosaccharides, an improved partial structure for the runner bean cell wall xyloglucan was proposed (O Neill and Selvendran, 1985b). It would appear that the xyloglucan does not contain a simple repeating unit but is composed of a block-type structure that is commonly encountered in plant polysaccharides (Stephen, 1983). 

The term hemicelluloses refers to substances which occupy the spaces between the cellulose fibrils within the cell walls of plants. Various studies, e. g., on apples, potatoes, and beans, show that xyloglucans dominate in the class Dicotyledoneae. A section of the structure of a xyloglucan from runner beans is presented in Formula 4.161. 

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