The effects of sulfur deficiency on the complement of proteins laid down in developing seeds of soybean (Glycine max L. Meff) have been examined. Sulfur deficiency caused a 40% decrease in the level of glycinins and a contrasting elevation in the level of 6-conglycinins. The subunit composition of these proteins was also affected. There was in particular a 3-fold increase in the j-subunit of 6-conglycinins in the sulfur-deficient seeds, and this accumulated largely as the B,-isomer of ,B-conglycinins, a protein which while virtually devoid of methionine and cysteine retains the physical properties of a normal 7S storage protein.These data demonstrate that a high degree of selectivity can be exerted by environmental stress over the accumulation of proteins in developing seeds.The amino acid compositions ofglycinins and 13-conglycinins, the major types of storage proteins of soybean (Glycine max L., Merr), vary sufficiently to affect their nutritional value in animal diets. Glycinins, in common with other legumin-like proteins from peas (Pisum sativum), lupin (Lupinus angustifolius), and broad bean (Vicia faba), contain more of the limiting amino acids cysteine and methionine, than the fl-conglycinins and other vicilin-like proteins. The composition of the glycinins and f3-conglycinins present in different soybeans is, however, not constant.Both glycinins and ,.-conglycinins are families of proteins assembled from a number of different subunits and these subunits also differ in their contents of the sulfur containing amino acids. The range is from 0.6 to 3% (w/w) methionine plus cysteine between the extremes ofglycinin subunits (12) and from virtually zero to 0.48% (w/w) for the subunits of the f3-conglycinins (14). Such differences between subunits provide the basis for the production of storage protein complements of substantially different nutritional values, and this paper is part of a study on factors which can affect such production.In other legume species, alteration in the growth conditions of plants from a normal nutrient supply to suboptimal conditions has been shown to alter the proportions of the major storage proteins present. In both lupin (3) and peas (7), sulfur deficiency specifically depressed the synthesis of particular sulfur-rich proteins. In peas, sulfur deficiency operated specifically by repression of the levels of legumin mRNA (1).In deficiency causes the production of greatly enhanced levels of the B0-isomer2 of,-conglycinin, a protein which, while virtually devoid ofmethionine and cysteine, retains the physical properties of a normal 7S storage protein (13, 16). We have shown in addition that the proteins in soybean are responsive to even the mild sulfur deficiencies likely to occur under field conditions, and predict that the already low cysteine and methionine contents of the soybean will be further depressed under these conditions to the detriment of its nutritional value. Plants subjected to specific sulfur deficiency received an equivalent medium containing magnesium chlorid...

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The temporal sequence of development of the major proteins of seeds of soybean (Meff.) has been studied during development of cotyledons from flowering to maturity. A well-defrned difference occurred in the tmes of appearance and the periods of maximum accumulation of a-, a'-, and /8-subunits of betaconglycinin. Whereas a-and a'-subunits appeared 15 to 17 days after flowering, accumulation of ,8-subunit did not commence until 22 days after flowering. Such alterations in subunit composition infer that changes also occurred in the amino acid composition of betaconglycinin during maturation, particularly in the content of methionine which is low in the l8-subunit.Marked changes occur in the proteins accumulating in cotyledons during seed development in many legume species (4,5,10,18). The yield and quality of the proteins eventually stored in mature seeds depends both on the relative rates of synthesis of these proteins and on the length of time for which such synthesis occurs. Variations both in the rates of synthesis of the major proteins, legumin and vicilin, and in the times at which their syDtheses commence have been demonstrated in developing cotyledons of Pisum sativum (9, 10). An ordered sequence of appearance also occurs among the group of proteins antigenically related to the mature vicilin fraction (10). Differences have also been shown between legumin and vicilin fractions in Viciafaba both in the time at which accumulation commences and also in the rates of synthesis (18).In soybean the major equivalent proteins are glycinin (11 S) and /?-conglycinin (7 S) (1, 6). Previous studies on developing soybean pods have shown that although proteins of both the 11 S and 7 S types appear early in cotyledonary development, there are major differences between the 7 S proteins in immature and mature cotyledons (5). During development a complex series of changes has been shown to occur in the proportions of three fractions obtained from the 7 S proteins by electrophoresis on polyacrylamide gels (5). Since it is now known that fi-conglycinin is composed of at least six isomers in mature tissue (13,17) the significance of these developmental changes is unclear.All the isomers of fl-conglycinin are combinations of only three major polypeptides, the a-, a'-, and ,8-subunits combined as trimers (14,15). In this paper, therefore, the 7 S proteins in developing soybean seeds have been reexamined under conditions which dissociate the secondary complexes. It is expected that the component polypeptides studied in this way should be related more directly to the primary products of protein synthesis.