Hemicelluloses in plants

Kauss, H. (1974) Biosynthesis of pectin and hemicelluloses. In Plant Carbohydrate Biochemistry, edited by J.B. Pridham, pp. 191-205. Academic Press, London and New York. 

Xylan, a xylose polymer having a pi,4-glycosidic linkage in the main chain, is the important component of hemicellulose in plant cell walls. Kobayashi et al. (121) reported that synthetic xylan that consists exclusively of xylose units can be prepared by the crude cellulase (containing xylanase) polymerization of P-xylobiosyl fluoride as a monomer in a mixed solvent of acetonitrile/acetate buffer. The reaction proceeded to produce Pl,4-linked synthetic xylan with a degree of polymerization of 23. 

Xylan is a D-xylose (Xyl) polysaccharide connecting through )5(1—>4) glycosidic linkage. It is one of the most important components of hemicellulose in plant cell walls (48). The structural difference between Xyl and Glc is C6 methylol group. The substitution position in disaccharide TSAS monomers is... 

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]. 

D-galactose, C HiiOe. Crystallizes in the pyranose form m.p. 1I8-120 C (monohydrate), 165-5" C (anhydrous). An isomer of glucose which is fairly widely distributed in plants. It is a constituent of raffinose and slachyose, of hemicelluloses, of pectin, of gums and mucilages, and of some glycosides. In animals it forms half the lactose molecule and is the sugar found in the brain. Chemically it is very similar to glucose. It has the structure... 

Hemicellulose [9034-32-6] is the least utilized component of the biomass triad comprising cellulose (qv), lignin (qv), and hemiceUulose. The term was origiaated by Schulze (1) and is used here to distinguish the nonceUulosic polysaccharides of plant cell walls from those that are not part of the wall stmcture. Confusion arises because other hemicellulose definitions based on solvent extraction are often used in the Hterature (2—4). The term polyose is used in Europe to describe these nonceUulosic polysaccharides from wood, whereas hemicellulose is used to describe the alkaline extracts from commercial pulps (4). The quantity of hemicellulose in different sources varies considerably as shown in Table 1. 

Xyloglucans are classified as gum when they are extractable with hot water from seed endosperm cell walls, such as the tamarind seed xyloglucan, and as hemicelluloses because they are alkali-extractable from the cell walls of vegetative plant tissues where they are closely associated with cellulose [2]. Also /3-glucans with mixed linkages appear under the name gum as well as hemicellulose in the literature. 

The number of reports about hemicelluloses that have been covered by this review indicates the significantly increased importance of all types of hemicelluloses as plant constituents and isolated polymers during the last decade. Attention has been paid not only to known hemicelluloses but also to the primary structure, physicochemical, physical, and various functional properties of hemicelluloses isolated from hitherto uninvestigated plants. The efforts to exploit a variety of plant as potential sources of hemicelluloses were pointed out particularly for agricultural crops, wood wastes, as well as for by-products of pulp and rayon fiber technologies. Many studies were devoted to characterize seed-storage hemicelluloses from plants that have been traditionally applied in food and medicine of many underdeveloped countries to find substitutes for imported commercial food giuns. 

Lignin is found in plant cell walls of supporting and conducting tissue, mostly the trac-heids and vessel parts of the xylem. It is largely found in the thickened secondary wall but can occur elsewhere close to the celluloses and hemicelluloses. 

Darvill, J. E., McNeil, M., Darvill, A. G., Albersheim, P. (1980). Structure of plant cell walls XL Glucuronoarabi-noxylan. A second hemicellulose in the primary cell walls of suspension-cultured sycamore cells. Plant Physiol, 66,1135-1139. 

In addition to cellulose certain related substances, namely hemicelluloses and lignin, occur widely in plants. 

Dietary Fiber. Dietary fiber is a broad term that encompasses the indigestible carbohydrate and carbohydrate-like components of foods that are found predominantly in plant cell walls (see Carbohydrates). It includes cellulose lignin, hemicelluloses. pentosans, gums, and pectins. 

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