Protein metabolism in seed germination

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Abstract
Etiolated seedlings, in which more than 38% of the N was present as asparagine, were grown from seeds of the blue lupin, Lupinus angustifolius. The retained plus regenerated protein N represented only 26.5% of the protein N of the embryos. The proteins in the embryos, and in the cotyledons and axial organs of the seedlings, contained respectively (on a N basis): 9.82, 7.43 and 5.35% amide N; 1.7, 251 and 254% tyrosine N; 0.62, 0.79 and 0.91% tryptophan N; 1.16, 1.43 and 1.09% cyst(e)ine N; and 0.24, 0.59 and 1.03% methionine N. From these analyses the axial-organ protein appears to have been approaching in composition those of the leaves of legumes. The cotyledons probably contained protein of similar composition mixed with incompletely broken down embryo protein. In the protein of the seedlings, it was possible to account for 17.3, 35, 36, 29 and 90%, respectively, of the amide N, tyrosine N, tryptophan N, cyst(e)ine and methionine N, originally present in the embryo protein. The embryo protein must be of low biological value on account of its very low methionine content. Whereas the seedling protein was probably of much higher biological value, germination probably resulted in a net loss of most of those amino-acids, present in protein and among the non-protein nitrogenous substances, which are dietary essentials. The possibility of the low methionine content of the embryo protein imposing a limitation upon protein regeneration in the etiolated seedlings is discussed.