Quantitation of growth retardation and transition to pyknotic forms following DHA treatment.

<p>(A) Early ring-stage PL7 parasites (1.5 h p.i.) were treated with a 3.5 h DHA pulse (1 μM) and the morphology of parasites (Giemsa smears) examined at 31 and 35 h after the drug pulse. Representative images of untreated and treated parasites are shown. The proportion of the parasite population corresponding to trophozoites (hemozoin-containing parasites) and non-trophozoites (rings or pyknotic forms) are indicated in the figure. (B) The size distribution of viable parasites (hemozoin-containing) in the drug-treated culture was quantitated and compared with untreated cultures at the indicated times after the drug pulse (<i>n</i> >50 per sample). Late rings are larger than early trophozoites and were counted as a separate category (filled grey bars). (C) PL2 (red) and PL7 (blue) parasites (1.5 h p.i.) were rendered unviable by treatment with a DHA pulse (1 μM, 3.5 h) and the fraction of unviable parasites exhibiting pyknotic morphology was quantitated (filled symbols). Open symbols denote untreated parasites. (D) Representative images of untreated PL2 parasites and treated unviable parasites showing ring-like and pyknotic morphologies (fraction of each morphology indicated).