Fig. 3. The plastid in S. neurona schizonts is a single tubular structure in close association with the nucleus and its spindles. Extracellular S. neurona merozoites (A-D) were fixed and incubated with an affinity-purified rabbit antiserum raised against the T. gondii plastid protein ACP (A) and DAPI (B). A single round organelle was detected close to the nucleus colocalizing with the extranuclear plastid DNA (arrowhead). S. neurona-infected cultures were fixed 48 hours post-infection (E-H), and simultaneously incubated with antibodies against ACP (green, E), -tubulin (red, F) and DAPI (G). The plastid in developing schizonts appeared to be a single tubule wrapped around the nucleus (H). (I-L) Transfection plasmids were constructed that place the genes of two plastid targeted proteins from T. gondii (FNR and ACP, fused to RFP (red) or YFP (green), respectively) under control of a S. neurona promoter element. Plasmids were introduced into S. neurona merozoites by electroporation prior to infection. Transformed cultures were observed by fluorescence microscopy in living cells 36 hours after transfection.