Transport microfibrils

Finally, it is possible that the glycoproteins, pectins, and hemicellu-loses are formed and cross-linked in blocks, and transported to the cell wall, where they react, possibly by non-enzyme-catalyzed mechanisms, with cellulose microfibrils. Such a membrane would presuppose that the... 

Electron-microscope investigation of cultures of bacteria has shown that the cellulose elements are not a physical appendage of the cell, but occur free and are scattered within the medium.This discovery has raised questions as to the processes or steps involved in the formation of the microfibrils and the extent to which they are influenced by cell organelles or carried out by exogenous chemical interactions and mechanical forces. Ohad and coworkers considered that the steps involved may be resolved into (a) polymerization of the activated, monomeric precursor to form cellulose molecules of high molecular weight, (b) transport of the molecule from the site of synthesis to that of crystallization, (c) crystallization or fibril formation, and (d) orientation of fibrils during deposition. 

Gas flow experiments [3] and our studies with different liquid viscosities (Figure 10) reveal that the voids are interconnecting and that fluid flow in these materials occur by mass transport. The flow rate is greatly reduced in high viscosity fluids. One can conclude, therefore, that these materials exhibit mechanical behavior greatly influenced by load bearing microfibrils, open to the environment. 

Differences in the structure of cell walls of various plants and their parts are related to the differentiation of the primary cells, cellulose crystalinity and the type and amount of non-cellulose polysaccharides. Deposition of additional layers of cellulose (in the form of clearly oriented parallel microfibrils), deposition of noncellulose polysaccharides and lignification of the polysaccharide network, which is due to polymerisation of phenolic compounds, results in the formation of thick secondary cell walls, which have various special functions. For example, they ensure the rigidity of tissues, transport of water and have protective and other functions. 

According to Figure 13.2, each fiber is formed by a central lumen surrounded by layers of fibrils and microfibrils. The lumen, responsible for transporting water and nutrients in the plant, is surrounded by a primary waU, three secondary walls (SI, S2, S3) and an intermediate wall [23,24]. 

---