THE FINE STRUCTURE OF THE EXOERYTHROCYTIC STAGES OF PLASMODIUM FALLAX

Abstract

The fine structure of the exoerythrocytic cycle of an avian malarial parasite, Plasmodium fallax, has been analyzed using preparations grown in a tissue culture system derived from embryonic turkey brain cells which were fixed in glutaraldehyde-OsO4. The mature merozoite, an elongated cell 3-to 4-/~ long and l-to 2-# wide, is ensheathed in a complex doublelayered pellicle. The anterior end consists of a conoid, from which emanate two lobed paired organelles and several closely associated dense bodies. A nucleus is situated in the mid portion of the cell, while a single mitochondrion wrapped around a spherical body is found in the posterior end. On the pellicle of the merozoite near the nucleus a cytostomal cavity, 80 to 100 m/~ in diameter, is located. Based on changes in fine structure, the subsequent sequence of development is divided into three phases: first, the dedifferentiation phase, in which the merozoite loses many complex structures, i.e. the conoid, paired organelles, dense bodies, spherical body, and the thick inner layers of the pellicle, and transforms into a trophozoite; second, the growth phase, which consists of many nuclear divisions as well as parallel increases in mitochondria, endoplasmic reticulum, and ribosomes; and third, the redifferentiation and cytoplasmic schizogony phase, in which the specialized organelles reappear as the new merozoites bud off from the mother schizont.

Cytoskeleton of Apicomplexan Parasites

“…4B). After growth and multiple nuclear divisions, polarized parasites are regenerated when the nuclei move to the schizont periphery and associate with the assembling IMC, subpellicular microtubules, and apical organelles (3,12,72,157) round shape and lack of apical specialization, replicating parasites are noninvasive during schizogeny. P. falciparum replication has been studied by observing microtubule structures during replication in red cells (130).…”

“…Subpellicular microtubules confer both elongated shape and apical polarity to apicomplexan parasites. Replicative forms or drug-treated parasites that lack subpellicular microtubules are nonpolar, nonmotile, and noninvasive (72,168). Subpellicular microtubules are organized by lateral association with the apical polar ring (APR), a circular MTOC (120,134).…”

“…Replication in Toxoplasma and Neospora occurs by endodyogeny, which creates two daughter parasites (63,71,91,154). Replication by Plasmodium, Theileria, Eimeria, and Babesia occurs by schizogeny, which can create 64 daughter parasites (3,12,72,79,150,157). The processes of endodyogeny and schizogeny are quite similar, differing mainly in the preservation or loss of maternal cell specialization.…”

Phylogenetic analyses suggest lateral gene transfer from the mitochondrion to the apicoplast

“…The DNA circle was localized in situ to a multimembranous structure, previously described as a 'spherical body' (e.g. Hepler et al, 1966) or a 'multimembranous vesicle' (e.g. Schrével, 1971), identified recently as a secondary vestigial plastid, and coined the term apicoplast (McFadden et al, 1997;Köhler et al, 1997).…”

Antimalarial Quinones for Prophylaxis Based on a Rationale of Inhibition of Electron Transfer in Plasmodium

“…Scheme I, as based on The search for the presence of coenzyme Qn in species of Plasmodium was successful, and mass spectral data and reversed-phase chromatographic results of Rietz et al (6) showed the presence of coenzyme Qs in P. lophurae. Vitamin (10) and Rudzinska and Trager (11) and the dependence of the parasite upon a gas phase containing a given concentration of oxygen are known; Anfinsen et al (12). Drugs General Procedure for 7-Alkylmercapto-6-hydroxy-5,8-quinolinequinones.…”