The Sulfur Content of Wheat Endosperm Proteins and Its Relevance to Grain Quality

Abstract

A distinction between sulfur-rich and sulfur-poor endosperm proteins is proposed on the basis of analyses of sulfur-deficient grain, of grain proteins labelled with 35S, and of heat-denatured proteins. Grain proteins from five wheat varieties, grown in pots with excess, normal or minimal supplies of sulfur, were examined by gradient gel and sodium dodecyl sulfate electrophoresis. Restriction of sulfur altered the proportions of proteins within and between protein classes. In particular, the proportion of the low-mobility gliadins (proposed as low-S) increased at the expense of the high- mobility gliadins. In addition, the low-S grain was severely depleted in all essential amino acids, though arginine and aspartic acid increased considerably compared to normal grain. Autoradiography following electrophoresis showed that the low-mobility gliadins contained no 35S whereas the high-mobility gliadins were well labelled. A further distinction between the two groups of gliadins was provided by heating a slurry of wholemeal at 130°C for 30 min: the low-mobility gliadin components were still readily extractable with 6% urea solution but the remaining gliadins (proposed as sulfur-rich) were not.