THE SOLUBILIZATION OF THE BASIC SUBUNIT OF SUGAR-BEET SEED 11-S GLOBULIN DURING PRIMING AND EARLY GERMINATION

The basic B-subunit of the seed storage protein 11-S globulin (an 11-S -legumin type protein) is the major polypeptide in soluble protein ext racts from primed sugarbeet (Beta vulgaris L.) seeds. In contrast, onl y a small amount of this protein is present in corresponding extracts from untreated dry mature seeds. Here, and as for all 11-S globulins d escribed so far, the B-chain is linked to other polypeptide(s), corres ponding most presumably to an acidic A-chain, through the formation of disulphide bridge(s). Polyacrylamide gel electrophoretic analyses of total and soluble protein extracts from untreated and primed seeds str ongly indicate that this priming-induced solubilization of the B-chain resulted from an endoproteolytic attack on the A-chain. Microscopical immunolocalization showed a uniform distribution of the 11-S globulin B-chain over the protein bodies of the embryonic cells from the untre ated seeds. For the primed seeds, however, the B-subunit of 11-S globu lin diffused out of the protein bodies and invaded the cytosolic compa rtment. This phenomenon occurred independently of the manner of primin g, being observed with hydroprimed and osmoprimed seeds, as well as wi th sugarbeet seeds that had been primed by a prehydration treatment. Q uantitative analyses of the amounts of soluble 11-S globulin B-chain h ave enabled the priming of sugarbeet seeds to be optimized.