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A synchrotron wide-angle x-ray scattering study of mung bean (Vigna radiata) primary cell walls was combined with published solid-state nuclear magnetic resonance data to test models for packing of (1→4)- β-glucan chains in cellulose microfibrils. Computer-simulated peak shapes, calculated for 36-chain microfibrils with perfect order or uncorrelated disorder, were sharper than those in the experimental diffractogram. Introducing correlated disorder into the models broaden the simulated peaks but only when the disorder was increased to unrealistic magnitudes. Computer-simulated diffractograms, calculated for 24- and 18-chain models, showed good fits to experimental data. Particularly good fits to both x-ray and nuclear magnetic resonance data were obtained for collections of 18-chain models with mixed cross-sectional shapes and occasional twinning. Synthesis of 18-chain microfibrils is consistent with a model for cellulose-synthesizing complexes in which three cellulose synthase polypeptides form a particle and six particles form a rosette. [ABSTRACT FROM AUTHOR]

Xyloglucans in the non-lignified primary cell walls of different species of monocotyledons have diverse structures, with widely varying proportions of oligosaccharide units that contain fucosylated side chains (F side chains). To determine whether fucosylated xyloglucans occur in all non-lignified walls in a range of monocotyledon species, we used immunofluorescence microscopy with the monoclonal antibody CCRC-M1. The epitope of this antibody, α-L-Fucp-(1→2)-β-D-Galp, occurs in F side chains. In most non-commelinid monocotyledons, the epitope was found in all non-lignified walls. A similar distribution was found in the palm Phoenix canariensis, which is a member of the basal commelinid order Arecales. However, in the other commelinid orders Zingiberales, Commelinales, and Poales, the occurrence of the epitope was restricted, sometimes occurring in only the phloem walls, but often also in walls of other cell types including stomatal guard and subsidiary cells and raphide idioblasts. No epitope was found in the walls of the commelinids Tradescantia virginiana (Commelinaceae, Commelinales) and Zea mays (Poaceae, Poales), but it occurred in the phloem walls of two other Poaceae species, Lolium multiflorum and L. perenne. The distribution of the epitope is discussed in relation to xyloglucan structures in the different taxa. However, the functional significance of the restricted distributions is unknown. [ABSTRACT FROM PUBLISHER]

Polysaccharides were located in the walls of normal and compression wood tracheids of Pinus radiata (radiata pine), Picea sitchensis (Sitka spruce) and Picea abies (Norway spruce) by transmission electron microscopy using immunogold labelling with monoclonal antibodies to (1→4)-β-galactan (LM5), (1→3)-β-glucan, arabinogalactan proteins (AGPs) (MAC207) and heteroxylans (LM10 and LM11). In fully differentiated compression wood tracheids, (1→4)-β-galactan was found in the S2(L) layer and, to a smaller extent, at the interface between the compound middle lamella and the S1 layer. (1→4)-β-Galactan appeared to be displaced from, or modified in, the S1 layer during cell wall formation. (1→3)-β-Glucan (callose) was confined to the helical cavities in the inner S2 layer of severe compression wood. MAC207 AGP glycan epitope was found exclusively in the S1 and S3 layers of normal wood tracheids and in the S1 and inner S2 layers of compression wood tracheids. Binding of LM10, which specifically recognizes unsubstituted or low-substituted xylans, occurred at similar locations to the MAC207 epitope, whereas binding of LM11, which recognizes more highly substituted as well as unsubstituted xylans, occurred throughout the tracheid walls with the exception of the primary wall. Immunogold labelling showed that the different wall layers of softwood tracheids have different polysaccharide compositions which change abruptly during cell wall formation. [ABSTRACT FROM PUBLISHER]

Except in the Poaceae, little is known about the structures of the xyloglucans in the primary walls of monocotyledons. Xyloglucan structures in a range of monocotyledon species were examined. Wall preparations were isolated, extracted with 6 M sodium hydroxide, and the extracts treated with a xyloglucan-specific endo-(1 → 4)-β-glucanase preparation. The oligosaccharides released were analyzed by high-performance anion-exchange chromatography and by matrix-assisted laser-desorption ionization time-of-flight mass spectrometry. Oligosaccharide profiles of the non-commelinid monocotyledons were similar to those of most eudicotyledons, indicating the xyloglucans were fucogalactoxyloglucans, with a XXXG a core motif and the fucosylated units XXFG and XLFG. An exception was Lemna minor (Araceae), which yielded no fucosylated oligosaccharides and had both XXXG and XXGn core motifs. Except for the Arecales (palms) and the Dasypogonaceae, which had fucogalactoxyloglucans, the xyloglucans of the commelinid monocotyledons were structurally different. The Zingiberales and Commelinales had xyloglucans with both XXGn and XXXG core motifs; small proportions of XXFG units, but no XLFG units, were present. In the Poales, the Poaceae had xyloglucans with a XXGn core motif and no fucosylated units. In the other Poales families, some had both XXXG and XXGn core motifs, others had only XXXG; XXFG units were present, but XLFG units were not. [ABSTRACT FROM PUBLISHER]

Xyloglucans (XG) with different mobilities were identified in the primary cell walls of mung beans (Vigna radiata L.) by solid‐state 13C‐NMR spectroscopy. To improve the signal:noise ratios compared with unlabelled controls, Glc labelled at either C‐1 or C‐4 with 13C‐isotope was incorporated into the cell‐wall polysaccharides of mung bean hypocotyls. Using cell walls from seedlings labelled with d‐[1‐13C]glucose and, by exploiting the differences in rotating‐frame and spin‐spin proton relaxation, a small signal was detected which was assigned to Xyl of XGs with rigid glucan backbones. After labelling seedlings with d‐[4‐13C]glucose and using a novel combination of spin‐echo spectroscopy with proton spin relaxation‐editing, signals were detected that had 13C‐spin relaxations and chemical shifts which were assigned to partly‐rigid XGs surrounded by mobile non‐cellulosic polysaccharides. Although quantification of these two mobility types of XG was difficult, the results indicated that the partly‐rigid XGs were predominant in the cell walls. The results lend support to the postulated new cell‐wall models in which only a small proportion of the total surface area of the cellulose microfibrils has XG adsorbed on to it. In these new models, the partly‐rigid XGs form cross‐links between adjacent cellulose microfibrils and/or between cellulose microfibrils and other non‐cellulosic polysaccharides, such as pectic polysaccharides. [ABSTRACT FROM PUBLISHER]

We examined ways in which dietary supplements of wheat bran may protect against colon cancer. The effects of supplementing the diet of female Wistar rats with 10% wheat bran on the disposition and metabolism of the dietary carcinogen 2-amino-3-methylimidazo[4,5-f ]quinoline (IQ) labelled with 14C was determined. Our data show that the wheat bran had a major effect on both the distribution and metabolism of IQ. At a low dose of IQ (1 mg/kg), we unexpectedly found that up to 2 h after gavage there were higher concentrations of radioactivity in the plasma of rats fed wheat bran compared with the controls, but there were lower concentrations of radioactivity after 2 h. At a high dose of IQ (50 mg/kg), there were always lower concentrations of radioactivity in the plasma of rats fed wheat bran compared with the control rats. One of the most marked effects of wheat bran was apparently to significantly retard the metabolism of IQ in the plasma when this was fed at either dose. There were also differences between the rats fed wheat bran and the control in the concentrations and types of IQ metabolites in the urine. [ABSTRACT FROM PUBLISHER]

The molecular ordering of cellulose, including its crystallinity, in the unlignified primary cell walls of three monocotyledons (Italian ryegrass, pineapple, and onion) and one dicotyledon (cabbage) was characterized by solid-state 13C NMR spectroscopy. These species were chosen because their primary cell walls have different non-cellulosic polysaccharides and this may affect the molecular ordering of cellulose. Values of the proton rotating-frame relaxation [T1p(H)] and spin-spin relaxation [T2(H)] time constants showed that the cellulose in the cell walls of all four species was in a crystalline rather than an amorphous state. Furthermore, a resolution enhancement procedure showed that the triclinic (Iα) and the monoclinic (Irβ) crystal forms of cellulose were present in similar proportions in these cell walls. However, the calculated cross-sectional dimensions of the cellulose crystallites varied among the cell walls (in the range 2–3 nm): the largest were in the Italian ryegrass, the smallest were in the onion and cabbage, and those of intermediate size were in the pineapple. The crystallite dimensions may thus be affected by the non-cellulosic polysaccha-ride compositions of the cell walls. [ABSTRACT FROM AUTHOR]