title: Cryo-electron tomography reveals four-membrane architecture of the Plasmodium apicoplast.
abstract: BACKGROUND
  The apicoplast is a plastid organelle derived from a secondary endosymbiosis, containing biosynthetic pathways essential for the survival of apicomplexan parasites. The Toxoplasma apicoplast clearly possesses four membranes but in related Plasmodium spp. the apicoplast has variably been reported to have either three or four membranes.
  
  
  METHODS
  Cryo-electron tomography was employed to image merozoites of Plasmodium falciparum and Plasmodium berghei frozen in their near-native state. Three-dimensional reconstructions revealed the number of apicoplast membranes and the association of the apicoplast with other organelles. Routine transmission electron microscopy of parasites preserved by high-pressure freezing followed by freeze substitution techniques was also used to analyse apicoplast morphology.
  
  
  RESULTS
  Cryo-preserved parasites showed clearly four membranes surrounding the apicoplast. A wider gap between the second and third apicoplast membranes was frequently observed. The apicoplast was found in close proximity to the nucleus and to the rhoptries. The apicoplast matrix showed ribosome-sized particles and membranous whorls.
  
  
  CONCLUSIONS
  The Plasmodium apicoplast possesses four membranes, as do the apicoplasts of other apicomplexan parasites. This is consistent with a four-membraned secondary endosymbiotic plastid ancestor.
authors: Parasitology, Department of Infectious Diseases, University of Heidelberg Medical School, Im Neuenheimer Feld 324, Heidelberg 69120, Germany.
authors: Leandro
authors: L
authors: Lemgruber
authors: Mikhail
authors: M
authors: Kudryashev
authors: Chaitali
authors: C
authors: Dekiwadia
authors: David T
authors: DT
authors: Riglar
authors: Jake
authors: J
authors: Baum
authors: Henning
authors: H
authors: Stahlberg
authors: Stuart A
authors: SA
authors: Ralph
authors: Friedrich
authors: F
authors: Frischknecht
mesh_terms: D020285:Cryoelectron Microscopy; D055032:Electron Microscope Tomography; D021621:Imaging, Three-Dimensional; D007425:Intracellular Membranes / Q000648:ultrastructure*; D052940:Merozoites / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D010962:Plasmodium berghei / Q000648:ultrastructure*; D010963:Plasmodium falciparum / Q000648:ultrastructure*; D018087:Plastids / Q000648:ultrastructure*