Submitted to: Korean Journal of Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/2002
Publication Date: 6/30/2002
Citation: KRISHNAN, H.B. BIOCHEMICAL AND ULTRASTRUCTURAL INVESTIGATION OF THE BREAKDOWN OF THE BETA-SUBUNIT OF BETA-CONGLYCININ DURING SOYBEAN (GLYCINE MAX [L.] MERR.) SEED GERMINATION. KOREAN JOURNAL OF CROP SCIENCE. 2002. V. 47(2). P. 85-94. Interpretive Summary: Globulins are the major seed storage proteins of soybean and make up 70% of the total seed protein. Some of the soybean seed proteins are not easily digestible. For example, in stimulated gastric fluid, spinach protein can be digested within 15 seconds, while the soybean seed proteins are stable for 60 minutes. Improving the digestibility of soybean seed proteins will improve the nutritional value of soy proteins. In this study, we have examined the fate of soybean seed proteins during seed germination and the associated anatomical changes. Results from this study will benefit scientists by providing basic information that is required to manipulate soy proteins for better digestibility. Farmers will also eventually benefit since they can obtain a premium price for soy proteins that have improved digestibility.
Technical Abstract: Antibodies raised against the purified beta-subunit of beta-conglycinin were used in immunohistochemical studies to monitor the pattern of beta- conglycinin mobilization. The first sign of beta-conglycinin breakdown was observed near the vascular strands and proceeded from the vascular strands towards the epidermis. The hydrolysis of beta-conglycinin occurred first near the abaxial surface while proteolysis at the adaxial surface commence 2 to 3 days later. In contrast to previous studies, Western blot analysis revealed that the breakdown of the beta-subunit of beta-conglycinin commenced as early as 2 days after seed imbibition (DAI). Most of the beta-conglycinin was degraded by 3 to 4 DAI. Concurrent with the degradation of the beta-subunit of beta-conglycinin, accumulation of 48, 28, and 26 kD proteolytic intermediates was observed from 2 to 6 DAI. Protein A-gold localization studies using thin sections of soybean cotyledons at different DAI revealed a gradual decrease in the protein A-gold labeling intensity over protein bodies at later stages of seed germination. During seed germination, the protein bodies in the storage parenchyma cells fused with each other and their contents became less and less dense. The protein bodies were converted into large central vacuoles by 8 DAI and contained very little storage protein. Results from this study demonstrate that the breakdown of the beta-subunit of beta-conglycinin commences much earlier that previously reported and identifies the 48, 28 and 26 kD polypeptides as the protolytic intermediates of beta-subunit of beta-conglycinin mobilization. Ultrastructural evidence for the temporal and spatial mobilization of beta-conglycinin during seed germination is also presented.