(1,3;1,4)-b-D-Glucan (b-glucan) accounts for 20% of the total cell walls in the starchy endosperm of wheat (Triticum aestivum) and is an important source of dietary fiber for human nutrition with potential health benefits. Bioinformatic and array analyses of gene expression profiles in developing caryopses identified the CELLULOSE SYNTHASE-LIKE F6 (CSLF6) gene as encoding a putative b-glucan synthase. RNA interference constructs were therefore designed to down-regulate CSLF6 gene expression and expressed in transgenic wheat under the control of a starchy endosperm-specific HMW subunit gene promoter. Analysis of wholemeal flours using an enzyme-based kit and by high-performance anion-exchange chromatography after digestion with lichenase showed decreases in total b-glucan of between 30% and 52% and between 36% and 53%, respectively, in five transgenic lines compared to three control lines. The content of water-extractable b-glucan was also reduced by about 50% in the transgenic lines, and the M r distribution of the fraction was decreased from an average of 79 to 85 3 10 4 g/mol in the controls and 36 to 57 3 10 4 g/mol in the transgenics. Immunolocalization of b-glucan in semithin sections of mature and developing grains confirmed that the impact of the transgene was confined to the starchy endosperm with little or no effect on the aleurone or outer layers of the grain. The results confirm that the CSLF6 gene of wheat encodes a b-glucan synthase and indicate that transgenic manipulation can be used to enhance the health benefits of wheat products.Cell wall polysaccharides account for about 10% of the dry weight of the mature wheat (Triticum aestivum) grain, and about 2% to 3% dry weight of the white flour fraction that is derived from the major storage tissue of the grain, the starchy endosperm (Stone, 1996). Although they are relatively minor components of white flour, the cell wall polysaccharides are immensely important in determining the properties of the flour for processing (Saulnier et al., 2007a) and in human nutrition, forming a major source of dietary fiber (Saulnier et al., 2007b;Topping, 2007).Wheat endosperm cell walls comprise two major components, arabino-(1,4)-b-D-xylan (arabinoxylan [AX]) and (1,3;1,4)-b-D-glucan (b-glucan), which account for about 70% and 20% of the total, respectively (Bacic and Stone, 1980). In addition about 4% cellulose [(1,4)-b-D-glucan] and 7% (1,4)-b-D-glucomannans are present (Bacic and Stone, 1980). This contrasts with starchy endosperm tissues of oats (Avena sativa) and barley (Hordeum vulgare), in which the proportions of AX and b-glucan are reversed (Henry, 1987;Stone, 1996). This is of particular interest as soluble b-glucans from barley and oats have benefits in reducing coronary heart disease that have been accepted by the U.S. Food and Drug Administration for health claims on food products (Anonymous, 2008). It is not known whether these benefits are shared by b-glucan from wheat, which differs from barley and oat b-glucans in its distribution of 1,3 and 1,4 lin...
A combination of enzyme mapping, FT-IR microscopy and NMR spectroscopy was used to study temporal and spatial aspects of endosperm cell wall synthesis and deposition in developing grain of bread wheat cv. Hereward. This confirmed previous reports that changes in the proportions of the two major groups of cell wall polysaccharides occur, with beta-glucan accumulating earlier in development than arabinoxylan. Changes in the structure of the arabinoxylan occurred, with decreased proportions of disubstituted xylose residues and increased proportions of monosubstituted xylose residues. These are likely to result, at least in part, from arabinoxylan restructuring catalysed by enzymes such as arabinoxylan arabinofurano hydrolase and lead to changes in cell wall mechanical properties which may be required to withstand stresses during grain maturation and desiccation.
Beyond its general role as antioxidant, specific functions of ascorbate are compartmentalized within the eukaryotic cell. The list of organelle-specific functions of ascorbate has been recently expanded with the epigenetic role exerted as a cofactor for DNA and histone demethylases in the nucleus. Compartmentation necessitates the transport through intracellular membranes; members of the GLUT family and sodium-vitamin C cotransporters mediate the permeation of dehydroascorbic acid and ascorbate, respectively. Recent observations show that increased consumption and/or hindered entrance of ascorbate in/to a compartment results in pathological alterations partially resembling to scurvy, thus diseases of ascorbate compartmentation can exist. The review focuses on the reactions and transporters that can modulate ascorbate concentration and redox state in three compartments: endoplasmic reticulum, mitochondria and nucleus. By introducing the relevant experimental and clinical findings we make an attempt to coin the term of ascorbate compartmentation disease.
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