Xylan from plant cell-walls

Xylans are partially extractable with water from natural cell walls but typically are removed by alkaline solution extraction. To minimize contamination by lignin, the plant or woody material is usually treated with azeotropic ethanol-benzene and the lignin removed by its conversion to halocellulose. The alkaline extract can be neutralized, precipitating the more linear, less acidic xylans. The more acidic, more branched xylan is recovered as a precipitate after addition of ethanol. 

Xylan is a polysaccharide of xilose with a P(1 4)-glycosidic linkage and it is an important component of hemicellulose in plant cell walls. Xylan was synthesised by a transglycosylation reaction catalysed by cellulase with the use of P-xylobiosyl fluoride as the substrate [207]. Cellulose-xylan hybrid polymers were synthesised by the polycondensation of P-xylopyranosyl-glucipyranosyl fluoride catalysed by xylanase (EC 3.2.1.32) from Trichoderma viride, in a mixed solvent acetonitrile/ acetate buffer (Scheme 12.23) [208]. 

The plant cell wall biology studies require more sensitive and specific probes to target individual wall components. Traditionally, antibodies have been the primary workhorses for the spatial localization of cell wall polysaccharides. Currently, nearly 30 monoclonal antibodies directed toward specific arabinan, galactan, xylan, galacturonan, fucosylated xyloglucan, and cell wall glycoprotein epitopes are available, from academic and commercial sources [172], Nevertheless, CBMs may be used for this purpose, since they present intrinsic specificity for individual carbohydrates. 

Xylan-type polysaccharides are the main hemicellulose components of secondary cell walls constituting about 20-30% of the biomass of dicotyl plants (hardwoods and herbaceous plants). In some tissues of monocotyl plants (grasses and cereals) xylans occur up to 50% [6j. Xylans are thus available in huge and replenishable amoimts as by-products from forestry, the agriculture, wood, and pulp and paper industries. Nowadays, xylans of some seaweed represent a novel biopolymer resource [4j. The diversity and complexity of xylans suggest that many useful by-products can be potentially produced and, therefore, these polysaccharides are considered as possible biopolymer raw materials for various exploitations. As a renewable resource, xylans are... 

Hemicelluloses are non-cellulosic low molecular weight polysaccharides that are found together with cellulose in plant tissues 1311. In the cell walls of land plants, xylan is the most common hemicellulosic polysaccharide, representing more than 30% of the dry weight 1321. Most xylans are heteropolysaccharides which are composed of 1,4-linked (3-D-xylopyranosyl residues 133, 134, 135). This backbone chain is substituted with acetyl, arabinosyl, and glucuronosyl residues 133. Homoxylans, on the other hand, consist of xylosyl residues exclusively and have been isolated from esparto grass 136, tobacco stalks 137, and guar seed husk 138. ... 

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