Microfibrils, cellulose

Fig. 3. A cross-section of a nearly square cellulose microfibril, with the individual molecular chains shown as rectangles. Also shown are the one- and two-chain unit cells of la and ip. This view of the microfibril is parallel to the long axis. The chains are arranged so that the edges of the crystal correspond...

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. 

Fig 1. Electron micrograph of a platinum/carbon replica prepared by the fast-freeze, deep-etch, rotary-shadow replica technique printed in reverse contrast. Cell walls of onion parenchyma have an elaborate structure with many thin fibres bridging between thicker cellulosic microfibrils. Scale bar represents 200nm. 

Replicas of the tomato cell walls are very similar to those of onion parench5una cell walls but replicas of the DCB-adapted walls did not show the structure of the walls clearly. The principle components of the adapted walls are shorter thinner fibres which seemed to form a gel-like structure with little evidence of long cellulosic microfibrils characteristic of the unadapted cells. It is possible that such a gel will bind water more strongly and reduce the amount of etching that takes place, resulting in a less well-defined replica (2). 

If cellulose exists in the cell wall as a network within a pectic matrix, the pectin that is within about 2nm of the cellulose network maybe on or near exposed surfaces of cellulose microfibrils. Both the gel and the eggbox pectins are represented in this low mobility spectrum. 

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. 

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

VanDerWelNN, PutmanCAJ, VanNoort SJT, DegrothBG, EmonsAMC. Atomic force microscopy of pollen grains, cellulose microfibrils and protoplasts. Protoplasma 1996 194 29-39. 

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. 

One xyloglucan had a measured axial ratio of about 100 (9). In the intact cell wall, the xyloglucan is firmly attached to the surface of the cellulosic microfibrils, principally by hydrogen-bonding (2,8,10-13), although some more secure bonds may also be present (2,10). 

Biogenesis of Cellulose Microfibrils and the Role of Microtubules in Green Algae... 

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