Are rhoptries of Coccidia really extrusomes?
Some evidence that rhoptries of invasive stages of Coccidia are extrusive organelles has been found in a study of Toxoplasma, after conventional electron microscopy, cryosubstitution preparations, and freeze-fracture. Periodic rows of intramembranous particles were seen in the membrane of the rhoptries. The ducts of the organelles are positioned by two microtubules, and joined to an apical vesicle, through the conoid. Above the vesicle in the plasmalemma, there is sometimes a "rosette" of intramembranous particles. Extrusion of a dense substance was seen at the same time as an anterior vacuole. This represents degenerative "empty" rhoptries. This paper discusses whether rhoptries of Coccidia can be put in the group of extrusomes of protists.
D000818:Animals; D002462:Cell Membrane / Q000648:ultrastructure; D005614:Freeze Fracturing; D007425:Intracellular Membranes / Q000648:ultrastructure; D008854:Microscopy, Electron; D009940:Organoids / Q000648:ultrastructure*; D014122:Toxoplasma / Q000648:ultrastructure*; D014617:Vacuoles / Q000648:ultrastructure