Turnover of Storage Protein in Seeds of Soya Bean and Pea

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Abstract
We were interested in determining whether the low protein content of pea seeds (Pisum sativum L.) as compared to soya bean seeds (Glycine max L. Merrill) might be due to faster degradation of the pea storage proteins during development of the seed. Pea and soya bean cotyledons were subjected to a ‘pulse-chase’ experiment using [3H]glycine in in-vitro cultures. In peas, legumin had a half-life of 146 days, while vicilin had a half-life of 39 days. There was no measureable degradation of soya bean storage proteins. Even with the pea storage proteins, the half-lives were so much longer than the maturation time of seeds that degradation of storage proteins could not account for the lower protein content of peas as compared to soya beans. The validity of these results was indicated by the finding that non-storage proteins had much shorter half-lives and that omission of a carbon or a nitrogen source greatly accelerated degradation. Labelled glycine was found to be a good probe for protein turnover studies because it was very rapidly metabolized.