Newly discovered linkages between the cortical (pellicular) ridges of Opalina

Samples of Opalina ranarum have been prepared for electron microscopy by ultra-rapid cryofixation followed by substitution fixation in a solvent containing tannic acid. This technique has made it possible to see that very thin linkages exist between the pleated ridges that form the surface of the cell. Between any two adjacent cortical ridges, the linkages, which are approximately 0.1 μm long, occur as a single row, 0.1 μm below the free edge, with an impressively regular spacing of 0.1 μm. The cortical ridges of the Opalinids are spaced with remarkable uniformity, even when thrown into undulating patterns. The linkages described here will inevitably stabilize the complex architecture of the cortex. Other possible functions are discussed.     

LINKAGE OF 5S RIBOSOMAL DNA TO OTHER rDNAS IN THE CHROMOPHYTIC ALGAE AND RELATED TAXA1

Gene organization within the nuclear ribosomal DNA cistron and linkage of the 5S rDNA gene to the cistron were surveyed in 20 taxa of protists representing most of the Chromophyta (stramenopiles) and representatives of the Dinophyceae (alveolata) and Euglenophyceae. The intergenic spacer, which separates adjacent cistrons, was first PCR-amplified from total DNA using primers anchored in the 3’end of the large subunit and the 5’end of the small subunit in the next downstream cistron. Presence of the 5S gene in the cistron was determined by a second round of PCR using primers anchored in the large subunit and the 5S gene. where 5S-linked rDNA was not detected in the cistron, the presence of 5S tandem repeating units were confirmed by the PCR of 5S-5S fragments from the total DNA. Results show that most of the Chromophyta, as well as Opalina, Proteromonas (colorless stramenopiles), Dinophyceae, and Euglenophyceae have a 5S-linked type of rDNA organization. In contrast, only tandem repeats of 5S rDNA were detected in Bacillariophyceae and Synurophyceae. The occurrence of 5S-unlinked rDNA is hypothesized to be the result of secondary transfer from an ancestral, linked 5S type. The 5S-linked type of rDNA organization is apparently common in protists. Given the fact that most of these protists have mitochondria with tubular or discoid cristae, as compared with flattened cristae common in higher plants and animals, we conclude that the 5S-linked type of rDNA diverged at a very early stage in the evolution of eukaryotes.     

Etude Ultrastructurale de Différents Types de Kystes d'Opalines

Deux types de structure kystique ont été observés au microscope éectronique. Dans le ler, qui correspond aux kystes d'infection ou gamontokystes, la cellule est relativement libre dans l'enveloppe kystique. Celle-ci est formée de 2 couches distinctes d'inégale épaisseur (ectokyste, endokyste) sécrétées par la cellule et doublées intérieurement par un mince feuillet cytoplasmique dûà une extension des plis cuticulaires. C'est la seule modification du cortex cellulaire. Par contre, dans le 2ème type les modifications sont beaucoup plus importantes. La cellule est étroitement accolée aux parois du kyste; crêtes et flagelles ont disparu de la surface. Cependant on retrouve leurs traces dans la région corticale, sous forme d'axonèmes intracytoplasmiques plus ou moins désorganisés et d'empilements de saccules associés à des rangées de microtubules. Ce seraient des kystes de résistance. Les structures observées dans ces derniers kystes nous permettent de discuter quelques idées sur la participation des microtubules et des systèmes membranaires à la morphogénèse du cortex des Opalines.     

Ecdysterone induced sexual reproduction in Opalina sudafricana parasitic in Bufo regularis

Ecdysterone induced sexual reproduction in Opalina sudafricana parasitic in Bufo regularis. International Journal for Parasitology 3: 863–868. Ecdysterone injections (0·5 mg/ml) induced sexual reproduction in Opalina sudafricana parasitic in male or female Bufo regularis after 12 days. Hypophysectomy or gonadectomy did not prevent the hormone from producing its effect on the parasites. Ecdysterone did not induce sexual reproduction in the parasites in vitro. Urine of toads injected with ecdysterone induced the opalinids to encyst in vitro.