Changes in proteins and amino acids in developing soybean seed and effect of phosphorus nutrition

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Abstract
Two varieties of soybean (Bragg and Punjab‐I) grown in pot culture with three levels of phosphorus were studied for the changes in protein content, ether extract, amino acids and protein fractions during the development of the seed, and the effect of phosphorus nutrition thereon was also studied. The non‐protein nitrogen, which formed a substantial portion of total nitrogen at early milky stage, decreased and true protein increased as the seed matured, but crude protein did not seem to alter much during the seed development, whereas ether extract gradually increased with maturity. The concentrations of free amino acids such as lysine, hydroxy‐proline and tryptophan decreased whereas those of glutamic acid and alanine increased as the seed approached maturity. However, the total concentration of methionine and tryptophan in the protein of the seed was not much affected by maturity. The albumin fraction decreased from the early milky stage to the maturity stage. Glutelin rapidly increased from the early milky stage to mid‐milky stage and sharply declined at the mature stage whereas the glycinin fraction rapidly increased from mid‐milky to the mature stage of seed development. The prolamine fraction did not vary during seed development. Phosphorus application increased crude protein and true protein and decreased ether extract but had little effect on amino acids and protein fractions.