Hemicelluloses biosynthesis

Role of phytate-derived MI in pectin and hemicellulose biosynthesis... 

Tenhaken, R., and Thulke, O., 1996, Cloning of an enzyme that synthesizes a key nucleotide-sugar precursor of hemicellulose biosynthesis from soybean UDP-glucose dehydrogenase. Plant Physiol. 112 1127-1134. 

Hemicelluloses are among the world s most abundant biopolymers. They are heteropolysaccharides present in large quantities in wood and the majority of plant tissues. The total global production of lignocellulosic materials in forests is estimated at 140 billion tons per year. The assumption that about 25 % of the lignocellulosic materials are hemicelluloses gives an estimation of the annual hemicellulose biosynthesis of 35 billion metric tons. 

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. 

Plant cell walls are complex, heterogeneous structures composed mainly of polymers, such as cellulose, hemicelluloses, and lignins. In spite of several decades of research, cell wall assembly and the biosynthesis and ultimate biodegradative pathways of individual polymers are still far from being fully understood. One simple example will suffice Even today, no enzyme capable of catalyzing cellulose formation in vitro has been obtained. 

Our electron microscopy observations have revealed some of the roles of cell organellae involved in biosynthesis of cell wall components (i) the plasma membrane is the site of cellulose synthesis. This supports the proposal that terminal and rosette complexes at the plasma membrane are responsible for cellulose synthesis, (ii) The Golgi-bodies and small circular vesicles derived from the r-ER s are involved in the biosynthesis and/or transport of the hemicelluloses. Our investigations, however, could not distinguish between what type of cell organellae contained what kind of hemicelluloses, and how these polymers were processed in the organellae. 

It was shown that, in the maturing seeds, while the synthesis of reserve hemicellulose progresses in the endosperm, a large amount of a trehalose is formed, in addition to sucrose and umbelliferose.92 This trehalose disappears rapidly during the progress of the ripening process, and umbelliferose accumulates continuously. It was predicted that the trehalose may be present in most umbellifers however, the relationship of this disaccharide to the biosynthesis of umbelliferose, and the mechanism involved therein, are not known. 

Amongst the cyclic polyols, inositols are most widely distributed in the plant kingdom.234 Out of nine stereoisomers, myo-inositol has the most widespread metabolic significance.235 The derivatives of myoinositol are also widespread. In plants, myo-inositol plays an important role in the biosynthesis of hemicelluloses and oligosaccharides it also occurs as a storage product (phytic acid), a coenzyme for sugar-transport, a precursor of phosphoinositides, and esters of in-doleacetic acid.47,113,238... 

No complete picture of biological materials can be given without reference to their original condition in their natural environment. Brief consideration will, therefore, be given to the biosynthesis of the hemicelluloses and to their relationship, in the plant, to cellulose and lignin. Since much of our present knowledge of the chemistry of the hemicelluloses is based upon examination of materials isolated by alkaline extraction from plant tissues which, in many cases, have been previously treated to remove lig-... 

Figure 18 O-Acetyl-4-O-methyl-D-glucuronoxylan, a type of hemicellulose, structure from angiosperms (Dekker, 1985) (reproduced by permission of Academic Press from Biosynthesis and Biodegradation of...

Atalla RH (1996) Cellulose and the hemicelluloses patterns for the assembly of lignin. In Lewis NG and Sarkanen S (eds), Lignin and lignan biosynthesis. American Chemical Society, Washington, DC, 172-9... 

The chemistry and biochemistry of wood have been summarized in several monographs. Numerous reviews of the chemistry of the hemi-celluloses are also available. " The chemistry of the polysaccharides associated with wood cellulose and the structural chemistry of the hemi-celluloses have previously been discussed in this Series. In the following, the structures and properties of all wood hemicelluloses will be considered in detail, and brief reference will also be made to their location in the wood. Topics not reviewed are evolution of wood hemicelluloses, their biosynthesis, their possible association with lignin in the wood, and their behavior in the technical pulping and bleaching processes. The hemicelluloses occurring in the bark of trees have also been omitted. 

Jones, O. T. (2004). The efifect of pH and hemicellulose derived inhibitors on xylitol biosynthesis. Masters thesis, Syracuse University, Syracuse, NY. 

Hemicelluloses are heteropolysaccharides. Their structure and polymeric properties vary depending on the origin, i.e., plant species, industrial processing, isolation and purification procedure. They are a heterogeneous group of polysaccharides. The term was coined at a time when the structures were not well understood and biosynthesis was completely unknown [6]. 

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