| Abstract: | A quick-freezing technique for freeze fracturing was used to determine periplast plate types in 20 cryptomonads. With this technique cells are frozen so rapidly that major artifacts are eliminated. We propose that periplast plates are attached to the cell membrane by intramembrane particles (IMP's), consequently plate shapes are outlined by IMP distribution in fractured membranes. Round to oval, sometimes slightly angular, plates occur in Cryptomonas ovata, Cryptomonas tetrapyrenoidosa, Cryptomonas parapyrenoidifera, Cryptomonas obovata, Cryptomonas erosa and two unidentified species of Cryptomonas; large rectangular plates occur in Chroomonas pochmannii, Chroomonas coerulea and Hemiselmis sp.; small rectangular plates were found in Cryptomonas sp. (Strain SDB); square to slightly rounded plates occur in Cryptomonas chrysoidea and a single continuous plate or sheet, perforated by ejectisome pores, was observed in Cryptomonas caudata, Cryptomonas rostratiformis, Cryptomonas marssonii, Cryptomonas platyuris, Cryptomonas curvata, Cryptomonas ozolini, Chilomonas paramecium and Rhodomonas sp. Oval and square plates are described for the first time in Cryptomonas. Plate IMP's may be morphologically modified in size and shape, depending upon their location in relation to the plate, the plate ridges, and ejectisome chambers. Conformational changes in plate shapes, to form hexagons or polygons, may be induced when cells are subjected to fixation, desiccation, cryoprotectants or centrifugation. |
