Nutritional control of storage protein synthesis in developing grain of wheat and barley

The availability of nitrogen and sulphur have major effects on thesynthesis of prolamin storage proteins in developing endosperms of wheat andbarley. A high level of available nitrogen results in an increased proportionofprolamin storage proteins. However, changes in the storage protein compositionoccur if additional sulphur is not also provided, with increased proportions ofsulphur-poor prolamins and HMW prolamins and decreased proportions ofsulphur-rich prolamins. In the case of wheat, this results in increasedresistance and decreased extensibility of dough for bread-making, withconsequences for the end-use quality. Further limitation in the availability ofsulphur results in decreased total prolamin synthesis and an increase in freeaspartic acid/asparagine in the grain. Recent studies of the structure andregulation of prolamin genes indicate the presence of regulatory elements inthepromoter regions of genes for S-rich and S-poor prolamins, which could respondto nitrogen levels, although the sensing and signal transduction mechanisms arenot understood. Such elements have not so far been identified in genes for HMWprolamins. Similarly, there is no information on how the availability ofsulphurcould modulate prolamin gene expression.