Ref ID : 7717
Franco Verni, Giovanna Rosati, and Nicola Ricci; The Cyst of Oxytricha bifaria (Ciliata, Hypotrichida). II. The Ultrastructure. Protistologica XX(1):87-95, 1984
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The ultrastructural investigation of the wall of the young cysts (24 hours old) of Oxytricha bifaria showed that it consists of a lamellar ectocyst (which gives rise to finger-like protrusions), a fibrous mesocyst, 2 µm thick, a structurally homogeneous endocyst and a granular layer which connects the cyst wall with the wrinkled cell surface. The study of the wall formation showed that, after the ectocyst, the granular layer and the endocyst are secreted while the mesocyst acquires its definitive morphology at the end of the process. At the same time the cytoplasm is denser and more compact than that of the vegetative cell while no appreciable change is noticeable in the macronuclear chromatin arrangement. Empty cysts of this age were also studied: it was found that not only the ectocyst is somewhere broken, but also that they lack the endocyst. Resting cysts about 14 day-old show the wall modified with respect to that of the young cysts. Their cytoplasm shows densely packed mitochondria, paraglycogen granules grouped in one single area and a very dense matrix. The macronuclear chromatin is now arranged in rather regular subspherical bodies. Some cysts lacking the endocyst were also found: their cytoplasm was quite irregular and rarefied. From these observations it appears that O. bifaria cysts are dynamic structures which can change in time the morphology of both the wall and the cytoplasm.