Proteolysis in the axis of the germinating pea seed : II. Changes in polypeptide composition

The radicle of the pea embryo (Pisum sativum L.) is known to possess a range of protein-degrading enzymes which could theoretically act in vivo to break down proteins stored in the radicle. However, most of the polypeptides of the radicle showed little evidence of net breakdown in vivo in the first 4 days from imbibition. One polypeptide, of mol. mass 13,000, was degraded almost completely between 1 and 2 days from imbibition; others, of mol. mass 84,000 and 30,000 were degraded within 4 days. The breakdown of polypeptides stored in the radicle (and plumule) is thus highly selective and closely regulated. The requirement for amino nitrogen in the growing axis is evidently met by the immediate export of amino acids from the cotyledons, rather than by massive breakdown of stored polypeptides in situ.