Ultrastructural Studies of a Vesicle System Associated with Endoplasmic Reticulum in Exo-Erythrocytic Forms ofPlasmodium berghei1

Abstract

Fine structural studies of a specialized vesicle system associated with the endoplasmic reticulum (ER) of exo-erythrocytic P. berghei suggest that this system may be the equivalent of a Golgi apparatus. Patches of ER, randomly distributed in the cytolasm of developing parasites, are formed of smooth and ribosome-studded cisternae intermingled with each other. The vesicle systems are located between and at the edges of ER aggregates and appear to be in different stages of budding from the cisternae. Prolonged osmication reveals distinct staining of the nuclear envelope and ER of the parasites and part of the Golgi apparatus of the mammalian hepatocytes. The small vesicles associated with the parasites ER are unstained as are the coated vesicles in the Golgi region of the liver cell. These sites in the parasite cytoplasm seem comparable to the concave surface of the Golgi apparatus in liver cells. The pinched-off vesicles fuse with others to form the prominent peripheral vacuolization characteristic of the nearly mature exoerythrocyte form. The formation of these peripheral vacuoles and their subsequent fusion with the parasite membrane may be an exocytosis mechanism supplying the rapidly expanding parasite with new plasma membrane material.