Changes in polypeptide composition and grain quality due to sulfur deficiency in wheat

Abstract

Qualitative and quantitative differences in protein composition were examined in 12 samples of flour milled from wheat (cultivar Olympic) grown under a wide range of sulfur and nitrogen inputs. Two-dimensional fractionation, comprising isoelectric focusing in one dimension and electrophoresis at pH 3 in the other, indicated that the changes in gliadin composition associated with sulfur deficiency involved the proportions of individual gliadins but not their charge, size or isoelectric point characteristics. Quantitative Polyacrylamide gel electrophoresis in the presence of SDS showed that sulfur deficiency resulted in increases in the proportions of polypeptides in the mol.wt. ranges 51,000 to 80,000 and above, but decreases in the proportions of lower mol.wt. polypeptides (8000 to 28,000, mainly albumins). The proportions of polypeptides in five size ranges were highly correlated with the sulfur to nitrogen ratios in the flour samples and also with their dough quality characteristics, particularly as measured with the Extensograph. Doughs produced from the variety, Olympic, usually are extensible but the increased proportion of high mol.wt. polypeptides, found in the sulfur-deficient samples, was associated with an increase in the toughness and a decrease in the extensibility of the dough.