Immunolocalization of ricin accumulation during castor bean (Ricinus communis L.) seed development

Ricin is a dimeric glycoprotein that accumulates in protein storage vacuoles of endosperm cells of Ricinus communis L. (castor bean). The proricin travels through the Golgi appar­atus and co-localizes throughout its route to the storage vacuoles of developing castor bean endosperm. We report here the pattern of seed morphological and ultrastructural changes during various stages of seed development, associated with ricin accumulation. ELISA was used to compare the ricin content in mature seeds of four Brazilian commercial cultivars. ELISA and immunoelectron microscopy anal­ysis were used to study ricin accumulation during seed development from 10 to 60 days after pollination (DAP). Results have shown that no ricin could be localized in the endosperm cells in the early development stages (before 20 DAP) and only a few localization points could be observed at 30 DAP. However, a significant ricin localization signal was observed at 40 DAP in the matrix of the protein storage vacuoles. The signal increased significantly from 50 to 60 DAP, when ricin was observed in both the matrix and crystalloids of the protein storage vacuoles. Understanding ricin expression at the cellular level is fundamental for the development of strategies for gene suppression using molecular breeding approaches.