Chemistry and Organization of Aleurone Cell Wall Components From Wheat and Barley

Abstract

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.