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In the primary walls of growing plant cells, the glucose polymer cellulose is assembled into long microfibrils a few nanometers in diameter. The rigidity and orientation of these microfibrils control cell expansion; therefore, cellulose synthesis is a key factor in the growth and morphogenesis of plants. Celery (Apium graveolens) collenchyma is a useful model system for the study of primary wall microfibril structure because its microfibrils are oriented with unusual uniformity, facilitating spectroscopic and diffraction experiments. Using a combination of x-ray and neutron scattering methods with vibrational and nuclear magnetic resonance spectroscopy, we show that celery collenchyma microfibrils were 2.9 to 3.0 nm in mean diameter, with a most probable structure containing 24 chains in cross section, arranged in eight hydrogen-bonded sheets of three chains, with extensive disorder in lateral packing, conformation, and hydrogen bonding. A similar 18-chain structure, and 24-chain structures of different shape, fitted the data less well. Conformational disorder was largely restricted to the surface chains, but disorder in chain packing was not. That is, in position and orientation, the surface chains conformed to the disordered lattice constituting the core of each microfibril. There was evidence that adjacent microfibrils were noncovalently aggregated together over part of their length, suggesting that the need to disrupt these aggregates might be a constraining factor in growth and in the hydrolysis of cellulose for biofuel production.

The avian eggshell is a highly ordered calcitic bioceramic composite, with both inorganic and organic constituents. The interactions between the inorganic and organic components within the structure are poorly understood but are likely to occur at the nanometre level. Thus structural variation at this level may impinge on the overall structural integrity and mechanical performance of the eggshell, and therefore analysis at this level is fundamental in fully understanding this ordered structure. In this study, structural changes in the mineral crystallites were investigated by microfocus small-angle X-ray scattering (µSAXS) using synchrotron radiation. Small-angle X-ray scattering (SAXS) can be used to investigate structures on the nanometre scale such as size, shape, arrangement and internal porosity. A microfocused X-ray beam, 1.5 µm vertically by 7 µm, was used to produce vertical linear scans of the eggshell section. SAXS patterns were taken from the eggshell membrane (inner surface of the eggshell) to the cuticle (outer surface of the eggshell). This allowed textural variations within the eggshell to be mapped. The scattering intensity profile was then used to derive the dimension of scattering objects that define the nanotexture. The nanotexture observed may result from the presence of the organic matrix, which is embedded as intracrystalline particles producing voids within the calcified framework of large (>1 µm) calcite crystals. Porod analysis revealed the average size of a scattering interface to be approximately 4.5 nm with small changes that had a depth-dependent variation. These were largest at the mammillary layer/membrane boundary. The palisade layer displayed a small upward trend in size of scattering object. Parallel scans showed that the textural variations observed within the palisade layer are significant and indicate local subtextures. In addition, many of the patterns exhibit diffuse scattering streaks that could result from reflectivity from the larger crystallite interfaces. Changes in the orientation of diffuse streaks were observed within the different layers, the membranes, mammillary layer, palisade layer, vertical crystal layer and cuticle, indicating certain preferred orientations of the crystallites within the layers. The nanotextural variations that are apparent could have implications at the macroscopic level of the resulting eggshell.