Structural studies of the polysaccharides of lupin seeds in relation to germination
Polysaccharides have been isolated from the flours of the ungerminated seeds of the lupins, Lupinus angustifolius, L. albus, L. luteus and L. mutabilis, and also from germinated seeds of the first two. Starch was absent from the seeds and L-arabinose and D-galactose were the most abundant sugar residues in the polysaccharides. The ratios of the former to the latter ranged from 22--48 to 100.The types of polysaccharides present, and their structural features, were established by methylation analysis and related analytical techniques. There were:- (i) a (1-> 4)-linked D-galactopyranan carrying terminal L-arabino furanosyl residues on some 6-O-positions. (ii) a much lower proportion of a 3-, and 6-, linked D-galactopyranan. (iii) a polysaccharide having 5-linked L-arabinofuranose residues. (iv) a complex L-rhamno-D-galacturonan which yielded three previously unreported acidic derivatives after methylation. (v) a non-cellulosic glucopyranan substituted by xylopyranose units. On germination of the seeds the (1-> 4)-D-galactan was identified as the reserve polysaccharide that was utilized. There was a simultaneous depletion in the amount of L-arabinose residues remaining. Studies were carried out on the methods employed for the various structural determinations including checking on:- (i) Completeness of hydrolysis of polysaccharides. (ii) Aspects of quantitation. (a) Losses during acetylation of glycitols and methylated glycitols. (b) Effect of dimsyl sodium and dimethyl sulphoxide on unmethylated polysaccharides. (c) Reduction of sugar residues before and after methylation of polysaccharides. (d) The reproducibility of designedly identical methylation techniques. (e) Recovery and analysis of components in methylation liquor-diffusates after dialysis.