Valonia microfibrils

Figure 10. E-fracture face of the plasma membrane during active synthesis of ordered microfibrils in secondary wall of Valonia macrophysa. Imprints of microfibrils run parallel to one another. TC s numbered 1 and 2 direct opposite ways to one another.

Figure 25. Freeze fractured replica. P-fracture face of the plasma membrane in 15h aplanospore of Valonia veniricosa. The clustered TC s are shown, suggesting the build-up of new axis for microfibril orientation.

Lamellar, single crystals of ivory-nut mannan were studied by electron diffraction. The base-plane dimensions of the unit cell are a = 0.722 nm and b = 0.892 nm. The systematic absences confirmed the space group P212121. The diffraction pattern did not change with the crystallization temperature. Oriented crystallization ofD-mannan with its chain axis parallel to the microfibril substrates, Valonia ventricosa and bacterial cellulose, was discovered ( hetero-shish-kebabs ). 

Cellulose is insoluble in water because of the high affinity of the polymer chains for one another. Its individual polymeric chains have molecular weights of 50,000 or greater. The molecular chains of cellulose interact in parallel bundles of about 2,000 chains. Each bundle constitutes a single microfibril. Many microfibrils arranged in parallel constitute a macrofibril, which can be seen under the light microscope. Figure 12.10 shows the inner cell walls of the plant Valonia the fibrils in the wall are almost pure cellulose. 

Lattice images of algal, bacterial, and ramie cellulose have been obtained. These images show the individual molecular chains and the sizes of microfibrils, which vary in size and shape according to the source of cellulose [242,243]. There is also some variation within a given source. For example, microfibrils of Valonia ranged from 150 to 250 A (15 to 25 nm). 

However, Marchessault and Sundararajan (1983) found no evidence of periodic disordered regions using dark field electron microscopy with Valonia ventricosa so they can be no larger than the limit of resolution (< 0.5 nm). Further, this hypothesis has contradictions. There is no logical reason why defects should be swept some distance along the microfibril rather than escaping laterally to the surface. 

Fig. 2.—Cellulose Microfibrils from Valonia macrophysa. (The purified cell-wall was mechanically dispersed in distilled water, dried, and shadowed. Note the tabular shape and the compound nature of the microfibrils.)...

Electron-diffraction measurements on cellulose microfibrils from Valonia show that the reciprocal-lattice points can be indexed, not by a Meyer-Misch unit cell, but by a unit cell having a and c periods twice as long. - This finding has been confirmed, and it is suggested that, although bacterial cellulose probably has the same unit cell, other native celluloses might differ. 

These characteristics confer very interesting mechanical properties on microfibrils. Transmission electron-diffraction methods have made a contribution to the quantification of the degree of crystalhnity. Thus, using the technique of image reconsfruction it was shown that, in the microfibril of Valonia cellulose, which has a diameter of about 200 A, there could be more than 1000 cellulose chains, all aligned parallel in an almost perfect crystalline array. 

Fig. 19. Molecular model of a microfibril of cellulose, projected along the fibril axes compared with the typical morphologies observed for Valonia cellulose and tunicin, along with the CPK (Corey-PauUng-Koltun) representation of the main crystalline faces for cellulose 1. (See Color Plate 12.)...

Fig. 20. Range of microfibril sizes for different sources of cellulose R is the ratio of the number of surface chains over the total number of cellulose chains. The estimated number of cellulose chains in one crystalline microfibril according to the origin of cellulose Valonia, 1200 Micrasterias, 900 tunicin, 800 cotton, 80 wood, 35 and parenchyma, 20.

Under partial acetylation, the size of Valonia cellulose crystals diminished in diameter such decrease is not homogeneous and corresponds to the loss of discrete fragments. At the beginning of the acetylation, the la phase is more susceptible to acetylation than the ip phase the latter appears more resistant. The missing fragments correspond to la domains, which are solubilized initially. These domains, which are more susceptible to acetylation, are acetylated first leaving behind exposed surfaces somewhat depleted in the la phase (Fig. 39). This confirms that in Valonia cellulose the la and Ip phases occur as discrete phases within the same microfibril. 

A prerequisite for this model of stmetural interconversion is the existence of arrays of parallel-packed chains in a single microfibril, the arrays being oriented in up and down directions. The occurrence of such an arrangement was demonstrated in the highly crystalline and well-organized cell-wall of Valonia. Cellulose microfibrils are statistically distributed in opposite polarities wifltin given arrays, where they are packed side by... 

Fig. 42. Dif action-contrast transmission electron microscopy of a fragment of Valonia ventricosa cell-wall cross-sectioned perpendicular to one of the main microfibrillar directions. The pictme is printed in reverse contrast, so that the cross-sectioned microfibrils appear as white squares. (See Color Plate 17.)...

J. F. Revol and D. A. I. Goring, Directionality of the fiber c-axis of cellulose crystallites in microfibrils of Valonia ventricosa. Polymer, 24 (1983) 1547-1550. 

Fractionation of the cellulose from the alga Valonia afforded a component of weight-average DP 4.4 x 10 , which is thought to determine the size of the template required for the synthesis of the polysaccharide. The synthesis of cellulose II growing at right-angles to the axis of the microfibril. An alkali-resistant chain structure. Cellulose I crystallizes after it is detached from the site of synthesis. 

Itoh T. and Brown, Jr. R.M., 1984. The assembly of cellulose microfibrils in Valonia macrophysa Kutz. Planta 160 372-381. 

Sugiyama I, Harada H., Fujiyoshi Y., and Uyeda N. 1985. Lattice images from ultrathin sections of cellulose microfibrils in the cell wall of Valonia macrophysa Rutz. Planta 166 161-168. 

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