Plants cellulose microfibrils

The filaments of all plant fibers consist of several cells. These cells form crystalline microfibrils (cellulose), which are connected together into a complete layer by amorphous lignin and hemi-cellulose. Multiple layers stick together to form multiple layer composites, filaments. A single cell is subdivided into several concentric layers, one primary and three secondary layers. Figure 5 shows a jute cell. The cell walls differ in their composition and in the orientation of the cellulose microfibrils whereby the characteristic values change from one natural fiber to another. 

Raman microscopy cellulose microfibrils in cell walls and distinguishing crystalline and noncrystalline inclusions Analysis of bioaccumulations in plant vacuoles ... 

Cellulose microfibrils make up the basic framework of the primary wall of young plant cells (3), where they form a complex network with other polysaccharides. The linking polysaccharides include hemicellulose, which is a mixture of predominantly neutral heterogly-cans (xylans, xyloglucans, arabinogalactans, etc.). Hemicellulose associates with the cellulose fibrils via noncovalent interactions. These complexes are connected by neutral and acidic pectins, which typically contain galac-turonic acid. Finally, a collagen-related protein, extensin, is also involved in the formation of primary walls. 

The detailed distribution of polysaccharides within cell walls can be determined by immunolabeling sections of plant tissues with appropriate antibodies (Knox, 2008). Such studies also show the distribution of polysaccharides in the middle lamella (Figure 3.5), which develops from the cell plate, formed at cell division, and is responsible for cell-cell adhesion. Cell comers (tri-cellular junctions) and the comers of the intercellular spaces can be regarded as extensions of the middle lamella. They are where stresses that tend to separate plant cells are concentrated and have been referred to as reinforcing zones (Jarvis et al., 2003). These zones and the middle lamella are rich in pectic polysaccharides, but contain no cellulose microfibrils (Jarvis et al., 2003). 

Chitin is the microfibrillar component of some fungal cell walls and is equivalent to cellulose microfibrils in plants. It is a characteristic feature of the Ascomycetes, Deuteromycetes and Basidiomycetes but is absent in the Phycomycetes, which contain cellulose as their major cell wall constituent. 

FIGURE 20-29 Cellulose structure. The plant cell wall is made up in part of cellulose molecules arranged side by side to form paracrys-talline arrays—cellulose microfibrils. Many microfibrils combine to form a cellulose fiber, seen in the scanning electron microscope as a structure 5 to 12 nm in diameter, laid down on the cell surface in several layers distinguishable by the different orientations of their fibers. 

Secondary-cellulose deposition occurs after cessation of expansion of the primary wall. Layers of the secondary wall, in contrast to the primary wall, display a very orderly, parallel arrangement of the microfibrils. In such plants as flax and hemp,1,2 bamboo,13 sisal,14-16 cotton hairs,2 and pine tracheids,13 three main layers can be detected in the secondary wall, each made up of cellulose microfibrils arranged in a helical fashion around the cell, In each of these secondary walls, the middle layer of cellulose is considerably thicker than the cellulose layers on each side of it, with a helical direction opposed to those of the latter. It is probable that each of these three layers is, in fact, complex, and made from a number of lamellae, each with its own helix of cellulose microfibrils.1 2... 

Ci activity (1,2), but / -glucosidase and cellobiase activities are probably ubiquitous (e.g., see Ref. 14 and 16). Whether or not these together constitute a cellulase complex as in fungi is unknown. The possibility seems unlikely since there are so few occasions in plants when whole cellulose microfibrils are autolyzed, and there is no need for it on nutritional grounds. Nevertheless, the question remains of why specific plant cells or tissues often elaborate more than one endocellulase. 

Hasezawa, S. and Nozaki, H. 1999. Role of cortical microtubules in the orientation of cellulose microfibril deposition in higher-plant cells. Protoplasma 209, 98-104... 

Cellulosic materials usually form crystal structures in part, and water cannot penetrate the inside of crystalline domains at room temperature. Native celluloses form crystalline microfibrils or bundles of cellulose chains 2-5 nm in width for higher plant celluloses and 15-30 nm for algal celluloses, which are observable by electron microscope. Almost all native celluloses have X-ray diffraction patterns of cellulose I with crystallinity indexes (Cl) 13] of about 40-95 %. 

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