Xyloglucan in cell walls of rice hull

Abstract

Rice hull was successively extracted with hot water (giving PS-I), 0.5% ammonium oxalate (PS-II), 4% potassium hydroxide (HC-I), and 24% potassium hydroxide (HC-II). By neutralization of the second alkaline extract, fraction HC-II was fractionated into subfractions HC-IIA (precipitated) and HC-IIB (not precipitated). To remove a xylan-like polysaccharide that contaminated HC-IIB, the fraction was treated twice with Streptomyces sp. endo-(1→4)-β- d-xylanase. Treatment of the xyloglucan-rich fraction from rice hull with partially purified Trichoderma viride cellulsae, followed by gel filtration on Bio-Gel P-2, yielded seven saccharide fractions, I–VII (V o). Fractions III, IV, and V, the main oligosaccharides derived from the xyloglucan, were purified by repeated gel-filtration on Bio-Gel P-2, and preparative paper chromatography. The structures of III, IV, and V were examined by determination of the molar ratio of component monosaccharides and of the degree of polymerization, methylation analysis, and hydrolysis with partially purified β- d-glucosidase from Aspergillus oryzae and purified α- d-xylosidase from Aspergillus niger. The structures of III, IV, and V were characterized as follows. ▪ The structure of the xyloglucan of rice hulls was shown to be similar to those of xyloglucans in the cell walls of rice seedlings and barley seedlings.