Polysaccharides plant, structure

The plant cell wall contains different types of polysaccharides, proteins (structural glycoproteins and enzymes), lignin and water, as well as some inorganic components (1, 14-16). The plant cell suspensions, however, grow as a population of cells with a primary cell wall(17). The main components of these walls are cellulose-free polysaccharides and pectic polysaccharides in particular, which constitute 1/3 of their dry weight. (18). Some fragments, e g. methanol, acetic, ferulic and p-cumaric acids, are connected with the pectic polysaccharides by ester bonds with the carboxylic and hydroxylic groups. 

While starch is the major structural polysaccharide, plant energy storage and regulation utilize a combination of similar polysaccharides that are referred to as starch. Starch can be divided into two general structures, largely linear amylose (structure 9.17) and largely branched amylopectin (structure 9.18). 

Plant structural material is the polysaccharide cellulose, which is a linear p (1 —> 4) linked polymer. Some structural polysaccharides incorporate nitrogen into their molecular structure an example is chitin, the material which comprises the hard exoskeletons of insects and crustaceans. Chitin is a cellulose derivative wherein the OH at C-2 is replaced by an acetylated amino group (—NHCOCH3). Microbial polysaccharides, of which the capsular or extracellular (exopolysaccharides) are probably the most important class, show more diversity both in monomer units and the nature of their linkages. 

Most carbohydrates exist in the form of polysaccharides. Polysaccharides give structure to the cell walls of land plants (cellulose), seaweeds, and some microorganisms and store energy (starch in plants and glycogen in animals). They are important in the human diet and in many commercial applications. 

Glucose is by far the most abundant monosaccharide it occurs free in fruits, plants, honey, in the blood of animals, and combined in many glycosides, disaccharides, and polysaccharides. The structure and properties of glucose will be considered in greater detail than those of the other monosaccharides, not only because of its importance, but because much of what can be said about glucose also can be said about the other monosaccharides. 

Glycogen is similar in structure to amylopectin, but branches more frequently (Figure 1.3). Starch and glycogen polysaccharides provide structures that are used for energy storage, in plants and animals respectively. 

Talmadge, K.W., Keegstra, K., Bauer, W.D. and Albersheim, P. 1973. The structure of plant cell walls. I. the macromolecular components of the walls of suspension-cultured sycamore cells with a detailed analysis of the pectic polysaccharides, Plant Physiol., 51(1) 158-173. 

The capacity of plant polysaccharides to structure flexible and functional surfaces, interfaces, and biological compartments. 

Apart from cellulose, many other polysaccharides help maintain plant structure. Among these are arabans and xylcms, which give wood many of its typical properties and are made from the pentose sugars arabinose and xylose. 

A number of plant [106, 178-183] and algal [64, 176] polysaccharides have structures based on a P(l-4)mannan main chain - P(l-4)mannan, a(l-6)galacto-P(l-4)-D-mannan and the related P(l-4)-D-glucomannan and galacto-P(l-4)glucomannan. They serve as cell wall structural material and as carbohydrate reserve polymers. An unbranched P(l-2) mannan of low molecular weight has been reported from the insect flagellate Herpetomonas samuelpessoai [184]. 

The terpenoids, which are composed of the five-carbon isoprenoids, constitute the largest family of natural products with over 22,000 individual compounds in this class having been described. The terpenoids (hemiterpenes, monoterpenes, sesquiterpenes, diterpenes, triterpenes, tetraterpenes, polyterpenes, and the like) play diverse functional roles in plants as hormones, photosynthetic pigments, electron carriers, mediators of polysaccharide assembly, structural components of membranes, and defense compounds. Many compounds used by man including resins, latex, waxes, and oils contain plant terpenoids. 

Ishii, T. Structure and functions of feruloylated polysaccharides. Plant Sci, 127, 111, 1997. 

Charnock S.J., Henrissat B., and Davies G.J. 2001. Three-dimensional structures of UDP-sugar glycosyltransferases illuminate the biosynthesis of plant polysaccharides. Plant Physiol 125 527-531. 

Tubers, roots, seeds and also some vegetative parts of plants contain non-starch storage polysaccharides, which are involved in processes associated with germination and growth. Most of these polysaccharides are structurally similar to non-cellulose polysaccharides of cell walls that are classified as hemicelluloses and pectins. The most important representatives of this group of polysaccharides are ... 

Talmadge, K. W., K. Keegstra, W. D. Bauer, and P. Albersheim The Structure of Plant Cell Walls. I. The Macromolecular Components of the Walls of Suspension-Cultured Sycamore Cells with a Detailed Analysis of the Pectic Polysaccharides. Plant Physiol. 51, 158 (1973). 

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