Plant Cell Monographs Volume 6, 2007, pp 57-88

Hemicelluloses and Cell Expansion

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Hemicelluloses are defined as wall polysaccharides that are not solubilized from wall materials with buffers, hot water, or chelating agents but only with more or less strong chaotropic agents such as alkali (O'Neill and York 2003). The most abundant hemicelluloses of the wall are xyloglucan, xylan, and mannans in their various forms. All of these polysaccharides have in common that, like cellulose, they consist of a backbone of β-1,4-linked d-pyranosyl residues but, unlike cellulose, they are branched and contain a variety of side chains. It is thought that the backbone structure of the hemicellulose leads to a strong non-covalent H-bond based association with cellulose microfibrils, thus forming a tight cellulose–hemicellulose network. In contrast, the side chains are responsible for a non-crystalline soluble form of parts of the polymer allowing, e.g., access to enzymes and other agents. Incorporation and metabolism of hemicelluloses is thus considered a key factor in the modulation of the load-bearing cellulose–hemicellulose network allowing cell elongation and plant growth to occur.