The Plasmodium cell-cycle: facts and questions.

The Plasmodium life-cycle contains within it several discrete cell-cycles whose molecular controls are very poorly understood. Of the five (or more) periods of DNA synthesis within the P. falciparum life-cycle, that associated with erythrocytic schizogony has been studied in the greatest detail and even here, controversy exists as to the precise nature and timing of the major, cell-cycle events. Thus, while it is clear that DNA synthesis (S phase) starts around 28-31h after merozoite invasion (soon after the appearance of pigmented trophozoites), neither flow-cytometric nor precursor-incorporation studies have provided a definite answer as to whether rapid and successive G2 and then M (mitotic) phases occur during schizogony. These and other problems of interpretation of the P. falciparum cell-cycle are considered.