Fine structure in cellulose microfibrils: NMR evidence from onion and quince

Abstract

SummaryIt has been controversial for many years whether in the cellulose of higher plants, the microfibrils are aggregates of 'elementary fibrils', which have been suggested to be about 3.5 nm in diameter. Solid-state NMR spectroscopy was used to examine two celluloses whose fibril diameters had been established by electron microscopy: onion (8-10 nm, but containing 40% of xyloglucan as well as cellulose) and quince (2 nm cellulose core). Both of these forms of cellulose contained crystalline units of similar size, as estimated from the ratio of surface to interior chains, and the time required for proton magnetisation to diffuse from the surface to the interior. It is suggested that the onion microfibrils must therefore be constructed from a number of cellulose subunits 2 nm in diameter, smaller than the 'elementary fibrils' envisaged previously. The size of these subunits would permit a hexagonal arrangement resembling the cellulose synthase complex.

Nanostructure of cellulose microfibrils in spruce wood

“…Primary-wall microfibrils from celery collenchyma are about 3 nm in diameter as estimated by methods similar to those used here (28,41). Other primary-wall microfibrils are either similar (74) or smaller (31,71,74) in diameter. C-6 conformations and H-bonding patterns in the disordered fraction of celery cellulose (28) were qualitatively similar to those reported here but primary-wall celluloses show consistent crystallographic differences, particularly the reduced monoclinic angle that has led these celluloses to be described as cellulose IV (48).…”

“…Microfibril diameters are calculated from NMR estimates of surface area (20,71) by assuming that all disordered chains are at the surface and that the mean thickness of the surface monolayer is 0.56 nm, averaged from the (110) and (1-10) d-spacings of cellulose Iβ (9). But a monolayer exposed at the (010) face in the rectangular model would be 0.82 nm thick, and these dimensions may in any case be altered by disorder.…”

Structural factors affecting 13C NMR chemical shifts of cellulose: a computational study

“…This assignment was based on the dominance of 89-ppm signals in highly crystalline cellulose and was tested by ball-milling microcrystalline cellulose sample which led to increased intensity of the 85 ppm peak and a simultaneous decrease in the intensity of the 89 ppm peak (Maciel et al 1982). The two peaks have also been assigned as the signals from solventexposed and interior chains, respectively (Ha et al 1998;Newman 1998). The intensity ratio between these two peaks gives information about the number of chains in the microfibril, which is consistent with the results obtained from diffraction methods and absorption spectroscopy, which collectively constrain the cross-sectional dimension of cellulose microfibrils (Fernandes et al 2011).…”

Expression of a Mutant Form of Cellulose Synthase AtCesA7 Causes Dominant Negative Effect on Cellulose Biosynthesis

“…The identification of the rosette complexes as the sites of cellulose synthesis was confirmed by the immunolocation of putative cellulose synthase catalytic subunits (CesAs) in the rosette subunits (Kimura et al, 1999). It is proposed that as many as 36 CesA protein molecules together with other putative associated proteins form one rosette complex, which produces 36 (1,4)-␤-glucan chains that polymerize and crystallize into a microfibril with an estimated diameter of 8 to10 nm (Ha et al, 1998). The monosaccharide donor substrate used by CesAs, UDP-Glc, has been postulated to be provided by membrane-associated form(s) of Suc synthase (Amor et al, 1995).…”