Effect of Sulphur Supply on the Seed Globulin Composition of Lupinus angustifolius

Abstract

Seeds from L. angustifolius grown at three levels of applied sulphur contain similar amounts of protein whereas the ratio of total nitrogen to total sulphur in the whole seed and in the extracted protein is greatly increased under sulphur deficiency. This large change in nitrogen to sulphur ratio is accompanied by suppression of the synthesis of conglutins α and γ which usually contain most of the sulphur-containing amino acids found in these seeds. This is balanced by synthesis of an increased amount of conglutin β which normally contains no methionine and a lower proportion of cystine. Studies of the protein subunit composition show that the overall molecular weight distribution of the polypeptides is independent of the level of sulphur, but under sulphur deficiency the higher molecular weight subunits do not contain the disulphide linkages normally present. It is not known whether these higher-molecular-weight conglutin β subunits are normally absent or present only in trace amounts in the seeds.