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A method is described for the isolation of wheat endosperm cell walls free from non-endospermic cell walls in a 70 % ethanol medium which prevents the loss of watersoluble polymeric components.

Methylation analysis and hydrolysis with specific enzymes indicates that aleurone cell wall preparations from wheat (Triticum aestivum cv. Insignia) and barley (Hordeum vulgare cv. Clipper) are composed of two main types of polysaccharides, heteroxylans and 1,3;1,4-β-glucans. Small amounts of glucomannan and cellulose are also present. Approximately 1% of a 1,3-β-glucan was also detected in the wall preparations using a specific 1,3-β-glucan exohydrolase. This material probably corresponds to the aniline blue-fluorescent deposits seen at the aleurone-endosperm interface. As isolated, the aleurone wall preparations are associated with protein, 10.5% in wheat and 16.0% in barley. Electron microscopic examination and amino acid analyses indicated that a major part of this protein arises from cytoplasmic protein deposited on the walls during isolation in organic solvents. Fractionation of the walls by conventional procedures showed that the heteroxylan and 1,3 ;1,4-β-glucan components were extracted by water, 8 M urea and alkaline solvents. Their differential solubility is discussed in terms of their structural organization and possible covalent interactions between polymers. Transmission electron microscopy of the walls at each stage of fractionation showed that the bilayered organization was retained after water and 8 M urea extraction but was lost following extraction in alkaline media.

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The water-soluble polymeric components of wheat endosperm have been extracted by two different procedures and their chemical composition studied in detail. Water extracts of wheat flour that had first been treated with hot 80% ethanol contained only 2% protein, but if the ethanol treatment was omitted up to 20% of the extracted polymeric fraction was low-molecular-weight non-dialysable protein material. Density-gradient ultracentrifugation in caesium chloride solutions indicated that most of this protein was free, whereas the 2% protein in the water extract of ethanol-treated flottr was firmly bound to a polysaccharide. This bound protein (a peptide) was characterized by high levels of hydroxyproline (16-20% of the amino acids present).Fractional precipitation of the water-soluble components with ammonium sulphate enabled the separation of a high-molecular-weight arabinoxylan (xylose : arabinose = 1·6 -1 . 9) and a lowmolecular-weight arabinogalactan (galactose :. arabinose =approx. 1· 5), the latter. being associated with the hydroxyproline-rich peptide.

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