Neutral Sugar Analysis of Tobacco Cell Wall Fractions

A method for the determination of the neutral sugar content of tobacco cell wall fractions has been developed. The seven neutral sugars - rhamnose, fucose, arabinose, xylose, mannose, glucose and galactose - determined in the analysis represent the usual glycosyl residues found in plant cell wall polysaccharides. In this procedure, the structural polysaccharides are acid hydrolysed into their constituent monosaccharides. The monosaccharides are then reduced with sodium borohydride to the corresponding alditols. The alditols are converted to the acetates with acetic anhydride. The alditol acetates are quantitatively measured by capillary gas chromatography with flame ionization detection. Both 72 % H₂SO₄ and 2 N trifluoroacetic acid have been used for acid hydrolysis of polysaccharides. Using model compounds, it was found that more complete recovery of the neutral sugars was obtained when the polysaccharide was hydrolysed with 72 % H₂SO₄. When the bright tobacco insoluble fraction was hydrolysed under these conditions, an H₂SO₄-insoluble residue remained. The neutral sugar method was applied to fractions isolated from bright tobacco. The results of the analysis provided a measure of the homogeneity of the cell wall fractions and thus helped indicate whether different types of structural polysaccharides were effectively separated from each other.