Significance of Con A binding sites in the conjugation ofEuplotes vannus

Ultrastructural aspects of the development of the cytoplasmic connection between mating cells of the ciliate Euplotes crassus

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.

Lectin binding sites in Paramecium tetraurelia cells. II. Labeling analysis predominantly of non-secretory components

All the lectin-FITC conjugates tested (ConA, RCA II, WGA) bind to the surface of Paramecium cells. Yet only WGA yields a distinct fluorescent pattern; it contours the basis of cilia and in some cells it brilliantly stains a few neighbouring rows of the regular surface fields in the anterioventral region (a region known to contain extensive fields of linear aggregates of freeze-fracture particles and to be engaged in conjugation). Incubation in vivo with WGA-FITC resulted in the selective labeling of the cytopharyngeal region as well as of the cytoproct. On Lowicryl K4M sections, WGA-gold probes concomitantly labeled disk-shaped vesicles that are assumed in the literature to serve as shuttle vesicles between these two cell regions and, thus, to connect forming and defecating digesting vacuoles (stages DV I and DV IV). On K4M sections WGA-Au stains also most other components of the lysosomal system. Also on K4M sections RCA II-Au labeled the walls of bacteria contained in DV I and II type digesting vacuoles (but not lysosomes identified bona fide by their size and shape and by their frequent vicinity to or continuity with digesting vacuoles). The WGA data largely support previous conclusions on the possible functional connection of all these elements (DV I-IV, smaller lysosomes, disk-shaped vesicles etc.) of the lysosomal system in Paramecium, as proposed by Allen and his group on the basis of other lines of evidence. As shown in the accompanying paper, ConA-FITC stained ghosts (formed after massive trichocyst exocytosis) also abut into DV-like structures. The different results obtained with the three lectins tested reflect the complex sorting machinery contained in the elaborate lysosomal system of a Paramecium cell. In the cytosol, finally, there occurs a particularly intense staining with ConA-gold, applied to Lowicryl sections, that probably represents glycogen-like particles. The same procedure reveals some weak staining of secretory contents and of nuclear structures.