Evidence for accumulation of the β-subunit of β-conglycinin in soybean [Glycine max (L) Merr.] embryonic axes

Abstract

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of total proteins from soybean cotyledons and embryonic axes revealed the presence of similar storage proteins in both organs. Results from Western blot analysis conducted with antibodies raised against the purified β-subunit of β-conglycinin demonstrated accumulation of the β-subunit in embryonic axes. This accumulation followed a temporal pattern similar to that shown by the cotyledons. Axis β-conglycinin was broken down during the initial stage(s) of seed germination and was completely mobilized within 3 days after imbibition. Subcellular fractions were isolated from developing embryonic axes using metrizamide density gradients and analyzed by Western blots. Storage proteins were enriched in the lighter fractions of the gradient as well as with immunoglobulin heavy-chain binding protein. Electron microscopy of the storage-protein-enriched gradient fraction revealed small vesicles and protein aggregates. Protein A-gold immunocytochemistry was used to localize the occurrence of the β-subunit of β-conglycinin within the protein aggregates present in the metrizamide gradient and in the protein bodies present in mature embryonic axes.