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Are rhoptries of Coccidia really extrusomes?
Abstract:
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.
Insights
Rhoptries in Coccidia, like Toxoplasma, are extrusive organelles. Evidence suggests these structures, containing unique membrane particles, function similarly to other protist extrusomes.
Area of Science:
- Cell Biology
- Parasitology
- Microbiology
Background:
- Rhoptries are key organelles in invasive protozoan parasites.
- Their precise function and classification remain areas of investigation.
Purpose of the Study:
- To investigate the extrusive nature of Coccidia rhoptries.
- To characterize the ultrastructure of rhoptries in Toxoplasma.
Main Methods:
- Conventional electron microscopy
- Cryosubstitution preparations
- Freeze-fracture electron microscopy
Main Results:
- Rhoptries exhibit periodic rows of intramembranous particles.
- Organelle ducts are associated with microtubules and an apical vesicle.
- Extrusion events correlate with anterior vacuole formation, suggesting degenerative processes.
Conclusions:
- Findings support the classification of Coccidia rhoptries as extrusomes.
- The study provides ultrastructural evidence for rhoptry extrusion mechanisms.