title: Ultrastructural aspects of the development of the cytoplasmic connection between mating cells of the ciliate Euplotes crassus.
abstract: Mating pair formation in Euplotes crassus involves homopolar orientation of two cells which eventually closely appose their ventral peristomial fields in such a way that the ciliary membranelles of the left margin of one field face the right margin of the other. Scanning and transmission electron microscopic observations revealed that the two apposed fields become united by a cytoplasmic connection, which develops at a precise site immediately adjacent to the membranelles nos. 14-18 and causes tearing off of a piece of the alveolar layer underlying the plasma membrane. The cytoplasm which starts bridging the mates' bodies contains a dense population of membrane-delimited vesicles and ribosome-like granules, and is outlined by nascent plasma membrane in some areas and preexisting plasma membrane of the cell cortex in others. In freeze-fracture replicas, this plasma membrane showed clear-cut distinctive aspects in relation to its age: whereas the preexisting plasma membrane appeared completely and uniformly covered with intramembranous particles, that nascent carried only a few particles and showed numerous irregular interruptions. These interruptions were supposed to represent sites where newly synthesized material is added to the membrane from the underlying cytoplasm.
authors.affiliation: Department of Evolutionary Biology, University of Siena, Siena, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Dallai
authors.forename: P
authors.initials: P
authors.lastname: Luporini