Higher plant celluloses

In the past few years, some impressive observations have been made by microscopists studying cells actively engaged in cellulose synthesis. It is now generally accepted by most workers that, in the bacterium A. xylinum, in most algae, and in all of the higher plants, cellulose is synthesized at the cell surface by an enzyme system localized in the plasma membrane. The notable exception to this conclusion concerns those algae which synthesize a cell wall composed of cellulosic scales such scales are synthesized intracellularly by way of the Golgi apparatus (see Ref. 57 and references cited therein). 

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 %. 

Figure 5 Changes in degrees of polymerization and yields of higher plant cellulose during acid hydrolysis at 80-95°C.

VanderHart and Atalla, approximately half of the upheld wing of C4 in the spectra of higher plant celluloses was attributed to the surface molecules of crystalline domains, Horii etal. indicated that their results conhrm the proposal of VanderHart and Atalla. It is to be noted that in their early reports in this area, Horii etal. used the designations [, and I to describe the different groups of celluloses in which the I and forms were dominant. However, in their more recent studies they have adopted the Iq, and I/3 designations. 

One of the discoveries growing out of the early diffractometric studies of cellulose was that it can occur in a number of allomorphic forms in the solid state, each producing distinctive X-ray diffractometric patterns. In addition to the cellulose II form, which has been discussed extensively, two other forms have been recognized these are cellulose III and cellulose IV. It is of interest to consider them briefly because they reflect the capacity of cellulose to aggregate in a wide variety of secondary and tertiary structures and because some of the higher plant celluloses produce diffraction patterns that are not unlike those of cellulose IV. Furthermore, they reflect the tendency for some of the celluloses to retain some memory of their earlier states of aggregation in a manner not yet understood. 

The previous studies (1-3) suggested that the higher plant celluloses, like cotton and ramie, were rich in Ig while the content was appreciable if not dominant in the algal celluloses and the bacterial cellulose obtained from Acetobacter xylinum. In Figure 2 the considerable contrast between the spectra of cotton linter cellulose, both dry (2A) and wet (2B), and algal cellulose (2C) from Valonla ventricosa is Illustrated. Because the lateral... 

Spectra of Several Native Celluloses. In Figure 3 the CP-MAS spectra of several higher plant celluloses are compared and are also contrasted to the spectrum of algal cellulose from Cladophora glomerata (bottom spectrum). In Figure 4, the spectra of two samples of bacterial cellulose from two different sources of Acetobacter xylinum, several algal celluloses, and the Cladophora, beaten at 1% solids consistency, are shown. 

The more dramatic spectral changes in Figure 6 are caused by strong acid hydrolysis, rather than beating. Spectra 6D and 6E appear to be "sharper-featured" (more crystalline) versions of the higher plant cellulose spectra (see Figures 2, 3 and 5). There is a dominant upfield shoulder at C4 compared to the downfield shoulder the central component of Cl is also greatly reduced. 

Figure 9 raises an Important question concerning crystalline polymorphy in the native celluloses. The hypothesis that higher plant celluloses like cotton and ramie are crystalline composites was suggested, in part, by the outer doublet and the sharper central feature of the Cl resonance in spectrum 9A. However, comparison of spectra 9A and 9C shows the central peak at Cl to be less intense at 200s compared with 1 ms, while the shape of the crystalline resonance at C4 remains constant. Since carbons C1-C5 relax at very nearly the same rates (32) in a T experiment, it is very likely that the signals for each of these carbons in... 

A survey of several native celluloses reinforced the similarity of the higher plant celluloses to one another, although limits of resolution and questions of chemical purity in the cellulose chains make comparison difficult and less meaningful. A parallel survey of NMR spectra from the more chemically pure algal celluloses and the bacterial cellulose, Acetobacter xylinum, indicated a general uniformity, albeit these spectra were distinct from the spectra of the higher plant celluloses. These algal cellulose spectra, however, showed small variations, outside of experimental error, which were taken as evidence for crystalline polymorphy. 

Chaln unit cell. They argued that algal celluloses consist of pure 8-chaln unit cells, whereas higher plant celluloses, like ramie, are mixtures of 2-chain and 8-chain unit cells. 

The first two higher plant cellulose synthase genes cloned, GhCesAl and GhCesAI, are transcribed during the secondary wall thickening phase of cotton fiber development [25]. 

Figure 17.1 Schematic representation of the components in higher-plant cellulose.

The ratio of these two allomorphs depends on the different sources of cellulose. Cellulose la is usually known to be predominant in bacteria and algae, while ip allomorph is prevalent in higher plants (Brannvall, 2007 Siqueira et al., 2010). However, Atalla and VanderHart have demonstrated some pecuharities in the NMR spectra of higher plants cellulose, which seemed to suggest that higher plants con-... 

Richmond T. 2000. Higher plant cellulose synthases. Genome Biology 1(4) reviews 3001.1-3001.6. Roberts A.W. and Roberts E.M. 2004. Cellulose synthase (CesA) genes in algae and seedless plants. Cellulose 11 419 35. 

Richmond T. 2000. Higher plant cellulose synthases. Genome Biol l reviews3001.1-3001.6. 

Cellulose is the most widespread natural organic compound. It occurs as a basic structural polysaccharide in the cell walls of higher plants. Cellulose is also found in green algae, fungi and, exceptionally, in cell walls of simple marine invertebrates (tunicates of the subphylum Tunicata). 

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