Plants primary cell walls

Glucomannans (GM) and galactoglucomannans (GGM), common constituents of plant cell walls, are the major hemicellulosic components of the secondary cell walls of softwoods, whereas in the secondary cell walls of hardwoods they occur in minor amounts. They are suggested to be present together with xylan and fucogalactoxyloglucan in the primary cell walls of higher plants [192]. These polysaccharides were extensively studied in the 1960s [6,193]. 

CelIulose.-Most biologists know that cellulose (l->4-linked P-D-glucan) is a polysaccharide component of all primary and secondary cell walls. Indeed, plant cell walls are... 

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. 

The components of the plant cell wall (8-21) are the middle lamella (intercellular substance), the primary wall, and the secondary wall. The middle lamella is the pectic layer between cells and holds adjoining cells together as do membrane carbohydrates. The primary wall is thin (1-3 pm) and flexible containing cellulose, hemicelluloses, pectins, and glycoproteins. This wall provides mechanical strength, maintains cell shape,... 

Fry SC, Miller JG. Toward a working model of the growing plant cell wall. Phenolic cross-linking reactions in the primary cell walls of dicotyledons. American Chemical Society, Washington, DC, 1989. 

Fluorescence occurs when radiant energy is absorbed and then, almost instantly, some of the energy is re-emitted, usually at a longer wavelength. Primary fluorescence (autofluorescence) occurs in flavo-proteins (13), plant cell wall materials such as lignin (7), and in flagella (14). Secondary fluorescence is when a material binds a fluorescent dye... 

Submicrofibril and triple-stranded left-hand helical microfibrils are found in tobacco primary cell wall and bacterial A. xylinum cellulose. We suspect from our results and the literature survey outlined in reference (1) that the triple stranded structures are prominent in the primary plant cell wall. The highly crystalline cellulose of plant and algae secondary cell wall appears by X-ray fiber diffraction (18,19) and TEM lattice imaging (20-23) to be largely crystalline arrays of planar straight chains of (l-4)-/3-D-glucan chains. 

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. 

The biochemistry of plant cell-walls is still at the stage of identifying and elucidating the covalent structures of the macromolecular components of the primary cell-wall. The secondary, tertiary, and quarternary structures of the polysaccharides therein have received only scant attention.29-32 The ultrastructural distribution of polymers within the wall, the integration of newly synthesized macromolecules into the wall, and... 

Fractionation and Chemistry of Citrus Pectic Polysaccharides. Pectic polysaccharides, commonly known as pectin, appear early in plant cell-wall formation. A series of complex biochemical steps results in the formation of cell plates followed first by its growth in area (primary cell wall) then in thickness (secondary cell wa.ll). Exclusive of randomly oriented cellulose fibrils, primary cell wall is composed mainly of pectic polysaccharides (34). These pectic polysaccharides are rich in D-galacturonic acid, D-galactose and L-arabinose residues. With growth in thickness of cell wall (secondary cell wall),there appears to be a replacement of pectic polysaccharide deposition with polysaccharides rich in D-glucuronic acid or 4-0-methyl-D-glucuronic acid,... 

How IAA can elicit profound changes in the size and form of a plant is totally unknown. At the cellular level it is known that the plant cell walls must be "softened" for growth promotion to occur (cf. 18J. Such effects, however, may be concomitants of growth and not the "primary" effects of auxin (19). 

Plants contain signiFcant concentrations of polysaccharides of which the potentially negatively charged oxygen functions can bind cations electrostatically or chelate them via polyhydroxy groups [89]. Particular attention was attracted by a structurally complex pectic polysaccharide rhamnogalacturonan-II (RG-II) [90]. This ubiquitous component of primary plant cell walls forms dimers cross-linked by 1 2 borate diol esters (dRG-II) that were found to complex in vitro sped be divalent cations and the majority of Ba, Pb, Sr, and rare earth elements (REEs) in fruit and vegetables [45, 91]. 

Many experiments have demonstrated the capacity of cellulases and of mixtures of cellulases, pectinases, and hemicellulases to break down or to soften plant cell walls. For human diets this would be beneficial in preparing infant or geriatric foods where reduced fiber content is desired. Recently treatment of wheat bran was found to increase the in vitro protein digestibility by 35% (63) and to increase weight gain of rats fed a bran-containing ration. The aleurone cell wall was the primary substrate for these enzymes. 

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