Figure 210

(A) Small schizont with few nuclei (N) but showing the initiation of daughter formation (D). Bar = 1 |im.

(B) Detail of a schizont showing the plate-like structures of the inner membrane complex representing the initiation of daughter formation (arrows). Ce, centriole; N, nucleus; NP nuclear pole; G, Golgi body. Bar = 0.5 |im.

(C) Low-power image of a large schizont with a number of nuclei showing the formation of a larger number of daughters. Bar = 1 |im.

(D) Detail showing the posterior growth on the inner membrane complex of the daughter to partially enclose the apicoplast (A), and nucleus (N). Note the anlagen of the rhoptry (R), and the conoid (C), in the apex of the daughter. Bar = 0.5 | m.

of organelles and are therefore viable. As daughter formation progresses by the posterior growth of the inner membrane complex, it encloses a nucleus, apicoplast, and mitochondrion (Figure 2.10D). In the apical cytoplasm, one or two electron-dense spherical structures representing the nascent rhop-tries (Figure 2.10D) and a number of cigar-shaped micronemes appear. The merozoites have relatively few dense granules, and these appear to form late in daughter development. This posterior growth continues until the merozoite is fully formed and contains the full complement of organelles.

In the apical cytoplasm there is maturation of the rhoptries, with the development of the duct leading to the conoid. In contrast to the tachyzoite and bradyzoites, the bulbous end of the rhoptry remains spherical. At this point the daughters fill the mother-cell cytoplasm but are still enclosed in the schizont plasmalemma. The final stage is the invagination of the mother-cell plasmalemma, starting at the anterior of the daughter and progressing posteriorly to form the outer membrane of the pellicle of each daughter (Figure 2.11A). A single micropore is formed in the pellicle just anterior to

0 0

Post a comment