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A finger-jointing model for describing ultrastructures of cellulose microfibrils.

ABSTRACT: In this paper, we propose a finger-jointing model to describe the possible ultrastructures of cellulose microfibrils based on new observations obtained through heating of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidized cellulose nanofibrils (CNFs) in saturated water vapor. We heated the micrometers-long TEMPO-CNFs in saturated water vapor (≥ 120 °C, ≥ 0.2 MPa) and observed a surprising fact that the long TEMPO-CNFs unzipped into short (100 s of nanometers long) fibers. We characterized the heated TEMPO-CNFs using X-ray diffraction (XRD) and observed the XRD patterns were in consistent with Iβ. We observed also jointed ultrastructures on the heated TEMPO-CNFs via high-resolution transmission electron microscopy (HR-TEM). Thus we concluded that cellulose microfibrils are not seamlessly long structures, but serial jointed structures of shorter blocks. Polysaccharide chains of the short blocks organized in Iβ. The jointed region can be either Iα or amorphous, depending on positions and distances among the chains jointed in proximity. Under heating, Iα was not converted into Iβ but was simply destroyed. The jointed structure implies a "working and resting rhythm" in the biosynthesis of cellulose.

SUBMITTER: Fugetsu B

PROVIDER: S-EPMC8115659 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Plant biomass represents an abundant and increasingly important natural resource and it mainly consists of a number of cell types that have undergone extensive secondary cell wall (SCW) formation. These cell types are abundant in the stems of Arabidopsis, a well-studied model system for hardwood, the wood of eudicot plants. The main constituents of hardwood include cellulose, lignin, and xylan, the latter in the form of glucuronoxylan (GX). The binding of GX to cellulose in the eudicot SCW represents one of the best-understood molecular interactions within plant cell walls. The evenly spaced acetylation and 4-O-methyl glucuronic acid (MeGlcA) substitutions of the xylan polymer backbone facilitates binding in a linear two-fold screw conformation to the hydrophilic side of cellulose and signifies a high level of molecular specificity. However, the wider implications of GX-cellulose interactions for cellulose network formation and SCW architecture have remained less explored. In this study, we seek to expand our knowledge on this by characterizing the cellulose microfibril organization in three well-characterized GX mutants. The selected mutants display a range of GX deficiency from mild to severe, with findings indicating even the weakest mutant having significant perturbations of the cellulose network, as visualized by both scanning electron microscopy (SEM) and atomic force microscopy (AFM). We show by image analysis that microfibril width is increased by as much as three times in the severe mutants compared to the wild type and that the degree of directional dispersion of the fibrils is approximately doubled in all the three mutants. Further, we find that these changes correlate with both altered nanomechanical properties of the SCW, as observed by AFM, and with increases in enzymatic hydrolysis. Results from this study indicate the critical role that normal GX composition has on cellulose bundle formation and cellulose organization as a whole within the SCWs.

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A finger-jointing model for describing ultrastructures of cellulose microfibrils.

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