Involvement of the Golgi apparatus in crystalloid protein deposition in Ricinus communis cv. Hale seeds

Abstract

The developing endosperm of castor bean has been used extensively as a model system for studies of storage-protein synthesis and processing, yet the path of transport of the storage proteins to the protein bodies has not been elucidated. In this study, immunolocalization of the 11S globulin (crystalloid protein) was performed on sections of acrolein–glutaraldehydefixed, resin-embedded, developing castor bean endosperm. Acrolein allowed rapid fixation of the tissue necessary for preserving the ultrastructure of the endomembrane system while maintaining adequate antigenicity of the target protein. Crystalloid protein was localized in the rough endoplasmic reticulum, the known site of synthesis, and in the dense proteinaceous inclusions within the protein bodies. In addition, significant labelling of Golgi complexes and associated vesicles, 65-nm diameter coated vesicles, and larger 220-nm diameter cytoplasmic vesicles was obtained. The findings provide the first direct evidence that the storage parenchyma cells of developing castor bean endosperm possess well-developed, functional Golgi complexes. This is consistent with previous observations of seed storage proteins in other plant species. The study further suggests that two distinct classes of vesicles are involved in the transport of the 11S globulin to the protein bodies. Key words: Golgi, immunolocalization, protein body, Ricinus communis, storage protein, transport (protein).