Abstract
Sulphur starvation resulted in decreases in the total sulphur content, and in the proportions of the sulphur-containing amino acids, cysteine and methionine, in the grain of pot-grown plants of the barley cultivars Sundance and Athos. The S-deficient grain contained a decreased proportion of storage protein (hordein) and increased non-protein nitrogen (NPN). Comparison of the amino acid compositions of the whole grain, and of the individual protein fractions, indicated that aspartate or asparagine was a major component of the increased NPN. Electrophoretic analyses showed that the hordein fraction was depleted in S-rich ‘B’ and ‘D’ hordein polypeptides, which was consistent with its low content of sulphur-containing amino acids. The salt-soluble protein fraction also contained low levels of cysteine and methionine, and SDS-PAGE showed that some bands, notably those of low molecular weight, were either greatly reduced in amount or were absent. It is suggested that these are non-essential components, possibly storage proteins. In contrast there was little effect on the amino acid or polypeptide compositions of the glutelin fraction.
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