Microfibril orientation

Summary Microtubule-Independent Control of Microfibril Orientation... 

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.

FIGURE 1.9 The different structural levels of a typical cellulose fiber the fiber wall consists of closely packed cellulose microfibrils oriented mainly in the direction of the fiber. 

Figure 22. Idealized drawing of cell wall layering showing microfibril orientation and the relative size of each layer...

Plant hormones rarely act alone hormones interact to produce a final effect. According to Gaspar et al., Some responses of plants to auxins may be caused by increased ethylene synthesis in response to auxin treatment. At high ethylene concentrations, microtubule and microfibril orientation are altered, which results in decreased cell elongation and increased cell expansion. The role of ethylene is hard to understand because it effects vary with developmental stage and because low concentrations can promote (or sometimes inhibit) a process, whereas higher levels have the opposite effect [22]. 

Ever since the discovery, by Ledbetter and Porter,88 of microtubules below the surface of the plasma membrane, suggestions have been made that these structures play some role in microfibril orientation. The suggestion arose because of two observations that (I) the orientation of microtubules has very frequently, but not always, been observed to be parallel to the orientation of the microfibrils most recently synthesized, and (2) agents, such as colchicine, that disrupt microtubules interfere with the orientation, but not the synthesis, of cellulose microfibrils. The literature pertaining to these studies has been well reviewed by Robinson,4 Schnepf and coworkers,89 Hepler and Palevitz,90 and Heath.91 In sum, the present evidence seems to favor some role for microtubules in orientation in some cases, such as the studies on guard cells by Palevitz and Hepler,92 and a series of papers on Oocystis by Robinson and coworkers,84,93-95 the case for micro-... 

Microfibril Orientation. Microfibrils are highly ordered groupings of cellulose that may also contain small quantities of hemicellulose and lignin. The exact composition of the microfibril and its relative niche between the polymeric chain and the layered cell wall... 

Figure 8. Representation of the microfibril orientation for each cell wall layer of Scotch pine with the chemical composition as a percent of total...

The rapid disappearance of these lamellae at EDR >4.6 suggests that when the chain tilt reaches at an angle, the lamellae suddenly broke into smaller blocks due to shear slip along the chain direction and are reorganized in microfibrils oriented along the draw direction. 

Originally hard-elastic PP was made from crystalline lamellar materials and was processed via melt spinning and crystallization under stress, followed by annealing under tension. The structure of the material consists of stacked crystalline lamellae (5-40 nm thick) with fold planes normal to the fiber direction. Between the lamellae, microfibrils oriented parallel to the draw direction are located. Under load, the lamellae tend to separate and voids bridged by fibrils appear. The void volume is initially about 18% at zero strain which increases to about 65% at 15% strain. No further increase in void volume was observed above 15% deformation. 

LLDPE/PET films were manufactured at a ratio of 70/30 (wt%) using various combinations of processing conditions (die diameter and drawing ratio), cooling conditions and microfibril orientation. The full details of the experimental design and film production parameters are given in [119,120]. 

Mizuta S. 1985. Evidence for the regulation of the shift in cellulose microfibril orientation in freeze-fractured plasma membrane of Boergesenia forbesii. Plant Cell Physiol 26 53-62. 

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