Structure and spacing of cellulose microfibrils in woody cell walls of dicots

Abstract

There may be differences between this version and the published version. You are advised to consult the publisher's version if you wish to cite from it.http://eprints.gla.ac.uk/105070/ Key words: WAXS; WANS; SANS; crystallinity; Scherrer; wood AbstractThe structure of cellulose microfibrils in situ in wood from the dicotyledonous (hardwood) species cherry and birch, and the vascular tissue from sunflower stems, was examined by wide-angle X-ray and neutron scattering (WAXS and WANS) and small-angle neutron scattering (SANS). Deuteration of accessible cellulose chains followed by WANS showed that these chains were packed at similar spacings to crystalline cellulose, consistent with their inclusion in the microfibril dimensions and with a location at the surface of the microfibrils. Using the Scherrer equation and correcting for considerable lateral disorder, the microfibril dimensions of cherry, birch and sunflower microfibrils perpendicular to the [200] crystal plane were estimated as 3.0, 3.4 and 3.3 nm respectively. The lateral dimensions in other directions were more difficult to correct for disorder but appeared to be 3 nm or less. However for cherry and sunflower, the microfibril spacing estimated by SANS was about 4 nm and was insensitive to the presence of moisture. If the microfibril width was 3 nm as estimated by WAXS, the SANS spacing suggests that a non-cellulosic polymer segment might in places separate the aggregated cellulose microfibrils. Abbreviations:NMR -Nuclear magnetic resonance; WAXS -Wide angle X-ray scattering; WANS -Wide angle neutron scattering; SANS -Small angle neutron scattering 2

Structure of native cellulose microfibrils, the starting point for nanocellulose manufacture

“…In secondary cell walls of dicots, small-angle neutron scattering studies indicated that the microfibrils were around 4 nm wide [34,43], exceeding the ca 3 nm width consistent with an 18chain structure ( figure 3). The small-angle scattering experiments required deuterium exchange at the interface to generate contrast [34], so the dimension concerned is probably across the hydrophilic faces of the microfibrils. The extra width has been attributed to interpolation of a xylan chain [34], fusion of the microfibrils over part of their length [34], or interpolation of bound water [43].…”

“…This contention is based on spindiffusion NMR experiments, indicating that the spatial separation between these two forms is less than the width of a microfibril, not tens of nanometres as required by the alternating model. Also, the alternating model requires an assumption that the disordered segments of the microfibril have an open structure permeable to water, to explain the observation that their hydroxyl protons exchange with D 2 O; but deuteration-wide-angle neutron scattering experiments showed that the spacing of the deuterated chains was no greater than in crystalline cellulose [10,34], consistent with these chains being located at a solid surface. The proportion of crystalline, C6-tg chains increases to 60% or more in celluloses like flax and cotton whose larger diameter gives them a smaller surface-to-volume ratio [29].…”

Functional Specialization of Cellulose Synthase Isoforms in a Moss Shows Parallels with Seed Plants

“…In vascular plants, both water-conducting tracheary elements and supportive fibers are characterized by helical (Barnett and Bonham, 2004) and aggregated (Donaldson, 2007;Fernandes et al, 2011;Thomas et al, 2014) cellulose microfibrils. The midribs of P. patens leaves include hydroid cells that transport water and stereid cells that provide support, but only the stereids have thick cell walls (Xu et al, 2014).…”

“…Secondary cell walls of water-conducting tracheary elements and supportive fibers are rich in cellulose, with microfibrils arranged in helices that vary in angle according to developmental stage and environmental conditions (Barnett and Bonham, 2004). Secondary cell wall microfibrils also are more aggregated than those of primary cell walls (Donaldson, 2007;Fernandes et al, 2011;Thomas et al, 2014). Recently, sum frequency generation (SFG) spectroscopy has been used to compare the mesoscale structure of cellulose microfibrils in primary and secondary cell walls.…”

“…Recent analyses of CSC and microfibril structure indicate that the rosette CSCs of land plants most likely contain 18 CESA subunits (Fernandes et al, 2011;Jarvis, 2013;Newman et al, 2013;Thomas et al, 2014;Oehme et al, 2015;Nixon et al, 2016;Vandavasi et al, 2016) in a 1:1:1 ratio (Gonneau et al, 2014;Hill et al, 2014). Seed plants have six phylogenetic and functional classes of CESA proteins, three required for primary cell wall synthesis (Desprez et al, 2007;Persson et al, 2007) and three required for the synthesis of the lignified secondary cell walls of tracheary elements and fibers (Taylor et al, 2003).…”