Vacuolation and Storage Protein Breakdown in the Castor Bean Endosperm following Imbibition

Abstract

Cytochemical staining of sections prepared for light microscopy, electron microscope sections, and sodium dodecyl sulphate-polyacrylamide gel electrophoresis reveal that, following imbibition, storage proteins are mobilized from the protein bodies of the endosperm of castor bean (Ricinus communis L. cv. Hale). This is accompanied by fusion of protein bodies to form a central vacuole, before all the protein is hydrolyzed. Mobilization of the US crystalloid protein complex and of the 2S albumin fraction commences 2 d after imbibition and is completed within 2 d. This loss of protein is accompanied by an increase in activity of three proteolytic enzymes, one carboxypeptidase and two -SH-dependent aminopeptidases. In contrast to the 11S and 2S protein fractions the lectins, located within the protein body, are mobilized only slowly and are present after the other proteins have been completely broken down. Hence lectins may have a role other than as storage proteins.