Left-handed helical cellulose microfibril

Triple-Stranded Left-Hand Helical Cellulose Microfibril in Acetobacter xylinum and in Tobacco Primary Cell Wall... 

RUBEN etal. Left-Hand Helical Cellulose Microfibril... 

Tobacco primary cell wall and normal bacterial Acetobacter xylinum cellulose formation produced a 36.8 3A triple-stranded left-hand helical microfibril in freeze-dried Pt-C replicas and in negatively stained preparations for transmission electron microscopy (TEM). A. xylinum growth in the presence of 0.25 mM Tinopal disrupted cellulose microfibril formation and produced a... 

Figure 1. Freeze-dried gel of A. xylinum cellulose ribbons deposited during normal growth. The arrows point to triple-stranded left-hand helical microfibrils averaging 36.8 3A in diameter (1). The sample was replicated with 17.3A Pt-C and backed with 90.2A of carbon. 

In tobacco primary cell wall the cellulose microfibrils observed individually or associated with bundles were also triple-stranded and left-hand helical. These observations are shown in Figure 10. Since cellulose is only 19% of the tobacco cell wall (17), the task of finding and identifying cellulose was complicated. For this reason A. xylinum which produces a pure ribbon of cellulose was used for studying cellulose structure. 

Submicrofibril and triple-stranded left-hand helical microfibrils are found in tobacco primary cell wall and bacterial A. xylinum cellulose. We suspect from our results and the literature survey outlined in reference (1) that the triple stranded structures are prominent in the primary plant cell wall. The highly crystalline cellulose of plant and algae secondary cell wall appears by X-ray fiber diffraction (18,19) and TEM lattice imaging (20-23) to be largely crystalline arrays of planar straight chains of (l-4)-/3-D-glucan chains. 

Figure 9. This model shows three left-handed helical submicrofibrils (SM) 1, 2 and 3 which emerged from the cell wall at their termini. It was not clear how the submicrofibrils first associated with other submicrofibrils but once associated they were spun together. This model assumed that cellulose synthesis provided the mechanical force that simultaneously extended and left-hand rotated the submicrofibrils, which in turn drove the secondary formation of three submicrofibrils into a left-hand helical microfibril (M).

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