Cell wall pectin layers

Several bioactive fractions from pea stem cell wall pectin have been separated. The fractions contained mainly galacturonides inhibited the process of root formation in thin cell-layer explants, while the fractions contained only neutral sugars stimulated this process to different extend. Analysis of the last fractions showed that they mainly consisted of galactan and arabinogalactan fragments. 

After multistep fractionation of cell wall pectin hydrolysate several bioactive fractions were obtained. They exhibited various influence on process of root development in buckwheat thin cell-layer (BTCL) explants (Table 1). 

The plant cell wall comprises layers of cellulose ml-croflbrlls embedded within a matrix of hemicellulose, pectin, extensin, and other less abundant molecules. 

The intermediate-mobility pectin can exist in any space in the cell wall more than 2nm away from cellulose microfibrils. It could therefore be in the middle lamella, cell comers or between layers of microfibrils in addition to the above proposal. The pectin seen in this part of the spectram are probably a heterogeneous mixture from a number of locations. 

This paper reports on the separation of some fragments obtained by acid hydrolyses of pectin from pea shoot cell walls, which had effect on thin cell-layer explant rhizogenesis. 

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,... 

The plant cell is surrounded by a cell wall, which determines many features of the plant. The outer layer of the cell wall are called middle lamella because it contains heavy layer of pectin (a polygalacturonan) that serves as the glue to hold one plant cell firmly to an adjacent cell. The inner layer of the wall is cell membrane. The cell membrane is completely different from the cell wall in form, composition, and function. Whereas the wall is a rigid, relatively thick structure, the cytoplasmic membrane is thin (approximately 75 A) and flexible. The membrane is composed of protein and lipid, whereas the wall is carbohydrate in nature. The wall provides support, whereas the membrane regulates the movement of substances into and out of the cell. 

The cell wall (Figure 5.5) is composed of a primary and a secondary wall surrounding a void, the lumen (F). The primary wall (0.1-0.2 pm) presents no particular arrangement and is constituted of cellulose, hemicelluloses, pectin, proteins and lignin. The secondary wall consists of three layers namely SI, S2 and S3, all of which are oriented layers of cellulose ... 

Underlying the waxy cuticle is the primary cell wall, which is composed of two distinct layers [108]. The outermost layer is comprised primarily of pectin substances (usually designated as pectin) in the form of free pectic acid (linear polymer of (1 4)-D-galacturonic acid)... 

Fig 1. The outer covering of land plants. W, wax rodlets L, lamellae of cutin and wax R, reticulate region of cutin and wax with cellulose fibrils P, pectin CW, cell wall of alternating layers of cellulose fibers and layers of hemicellulose plus pectin PL, plasmalemma E, ectodesma. (Reproduced with permission from Ref. 2. Copyright 1983 Edward Arnold.)... 

A FIGURE 6-33 Schematic representation of the cell wall of an onion. Cellulose and hemicellulose are arranged into at least three layers in a matrix of pectin polymers. The size of the polymers and their separations are drawn to scale. To simplify the diagram, most of the hemicellulose cross-links and other matrix constituents (e.g., extensin, lignin) are not shown. [Adapted from M. McCann and K. R. Roberts, 1991, in C. Lloyd, ed.. The Cytoskeletal Basis of Plant Growth and Form, Academic Press,... 

Most plants contain pectin in the intercellular layer between the primary cell walls of adjoining cells. Six to seven million kg of purified pectin are produced annually, more than half of which is extracted from citrus peel C. ) Of this amount, 80 to 90% is used in the manufacture of jellies, jams, and similar products ( ). In this chapter, jelly will be used to denote the product formed from pectin, sugar, and acid under specific conditions. Gel will mean a similar physical state but not the commercial product O). 

The distribution of constituents is quite simple in cotton. The secondary walls of cotton fibers consist almost entirely of highly crystalline cellulose. Almost all the hemicelluloses and extraneous materials (waxes, pectins, and certain nitrogenous substances) are contained in the cuticle and primary wall layers. In wood, on the other hand, the non-cellulosic materials are deposited in all regions of the cell walls from the lumen through the compound middle lamella. 

As already noted (see p. 327), some experimental evidence has been educed for parallel orientation of the microfibrils in crossed layers under the influence of 0-(carboxymethyl)cellulose. It has been proposed that microfibrils in the plant cell-walls are oriented in the same way under the influence of charged polysaccharides (such as pectins) found in the middle lamella and the primary wall (see p. 348). 

Pectins are complex, macromolecular compounds that occur in all higher plants. They are found in the cell walls, particularly in the intercellular layers, and in some ripe fruits and plant juices. 

The secondary wall found in wood cells is composed of two or three layers, known as SI, S2, and S3, respectively. In each of these layers, the cellulose microfibrils are "spirally-wound" at a different angle to the major axis of the tracheid. This variation in microfibril angle imparts strength to the fiber structure in a variety of directions. Within the bast or schlerenchyma cells found in flax, hemp, jute, and kenaf, the secondary wall is less thick than that of wood, but contains layers of similarly spirally-wound microfibrils embedded in a hemicellulose and pectin-rich matrix. This "composite structure" imparts potentially high strength to regions of the cell wall. Figures 9.1 and 9.2 show a schematic representation of flax fiber and a section of an elementary fiber with its fibrillar structure in its secondary cell wall [31]. 

The primary cell-wall is actually a glycoproteinaceous layer composed of pectin, cellulose, hemicellulose, and proteins. As the cell ages and differentiates, it secretes new materials, which form a mixture with the constituents of the primary cell-wall and... 

The fully developed cotton fibre consists of a waxy cuticle that envelopes it, a cell wall that is differentiated into primary (outer) and secondary (inner) layers and residual protoplasm called the lumen. Although this concept of the fibre structure persists, more recent ideas do not differentiate between the cuticle and the primary wall, which is less than half a micrometer thick and consists of around 50% cellulose, with pectin, waxes and proteins making up the remainder. The secondary wall, which differs considerably in chemical composition and structure from the primary wall, consists of up to 95% cellulose. ... 

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