Mobilization of storage proteins in soybean seed (Glycine max L.) during germination and seedling growth

Abstract

During germination and early growth of the seedling, storage proteins are degraded by proteases. Currently, limited information is available on the degradation of storage proteins in the soybean during germination. In this study, a combined two-dimensional gel electrophoresis and mass spectrometry approach was utilized to determine the proteome profile of soybean seeds (Glycine max L; Eunhakong). Comparative analysis showed that the temporal profiles of protein expression are dramatically changed during the seed germination and seedling growth. More than 80% of the proteins identified were subunits of glycinin and beta-conglycinin, two major storage proteins. Most subunits of these proteins were degraded almost completely at a different rate by 120 h, and the degradation products were accumulated or degraded further. Interestingly, the acidic subunits of glycinin were rapidly degraded, but no obvious change in the basic chains. Of the five acidic subunits, the degradation of G2 subunit was not apparently affected by at least 96 h but the levels decreased rapidly after that, while no newly appearing intermediate was detected upon the degradation of G4 subunit. On the other hand, the degradation of beta-conglycinin during storage protein mobilization appeared to be similar to that of glycinin but at a faster rate. Both alpha and alpha' subunits of beta-conglycinin largely disappeared by 96 h, while the beta subunits degraded at the slowest rate. These results suggest that mobilization of subunits of the storage proteins is differentially regulated for seed germination and seedling growth. The present proteomic analysis will facilitate future studies addressing the complex biochemical events taking place during soybean seed germination.