Figure 1: Ultrastructural changes in P. falciparum gametocytes during activation. (a) Transmission electron micrograph of a mature, non-activated gametocyte. The erythrocyte is reduced to an electron-light hem. The PVM is located adjacent to the PPM and the PV is therefore not discernable. No osmiophilic bodies are detectable, indicating that a male microgametocyte is pictured. Inset shows the pellicular membrane complex, depicting the SPM (1), the PPM (2) and the PVM (3). (b) A female macrogametocyte two-minute postactivation. The gametocyte is in the process of rounding up, thereby loosing its crescent shape. The osmiophilic bodies become closely associated to the parasite surface. At the poles, the PVM separates from the PPM and the erythrocyte is in the process of degrading (arrowheads). (c) Ultrastructure of an exflagellating microgametocyte. The axoneme of a forming microgamete is visible as longitudinal section, and several other cross sections of axonemes are detectable inside the microgametocyte. The PVM has disappeared and the EM ruptured. (d) A female macrogamete after emergence. This stage is marked by pronounced ER and the highly branched single mitochondrion. The SPM is in the process of disintegrating (arrowheads). A, axoneme; EM, erythrocyte membrane; ER, endoplasmic reticulum; FV, food vacuole; M, mitochondrion; N, nucleus; OB, osmiophilic body; PPM, parasite plasma membrane; PV, parasitophorous vacuole; PVM, PV membrane; SPM, subpellicular membrane. Bar, 1 m.