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with a “parental” phenotype expressed by the old macronuclei and a developing phe- notype expressed by the genome residing in the “new” macronucleus. Replacement of the “paren- tal” macronuclei occurs over several cell divisions following conjugation , and the new phenotype presumably becomes established as the “paren- tal” macronuclei are diluted out by cell division cycles. Since renewal of the macronuclei is not directly connected with conjugation, Raikov sup- poses this to be an ancestral feature of the conjuga- tion process (see also Orias, 1991a, 1991b). 5.7 Other Features Gram-negative bacteria are commonly associated with karyorelicteans . Geleia species may have perhaps 10,000 bacteria as epibionts on their cell surface (Epstein, Bazylinski, & Fowle, 1998). Other Gram- negative bacteria are found in the cytoplasm. Since they are often not bounded by a ciliate vacuolar mem- brane, it is assumed that they are endosymbionts. Their functional relationship to their hosts is unknown. A novel feature restricted to the loxodid karyo- relicteans is the organelle known as Müller’s vesicle . The vesicle, about 7 µm in diameter, encloses the Müller’s body , which itself is bounded by a cell membrane that encloses barium salt-dominated crystals in the freshwater Loxodes and strontium salt- dominated crystals in the marine Remanella (Rieder, Ott, Pfundstein, & Schoch, 1982). Movements of the Müller’s body , in response to gravity and the orientation of the ciliate, may deform ion channels on the cell surface and thereby modulate cell move- ment. Movement in Loxodes is also dependent on external oxygen concentration in the water: Loxodes swim faster upward when the water is anoxic and faster downward when the water is oxygen-saturated (Fenchel & Finlay, 1984, 1986b). Müller’s body is suspended in the vesicle by a stalk that is a supported by postciliary microtu- bules from an adjacent dorsal left somatic dikinetid (Fenchel & Finlay, 1986a). These dikinetids com- prise the loxodid dorsolateral kinety that Foissner (1998b) has presumed to be homologous to a somatic kinety of kentrophorids that is in a similar position but does not “bear” Müller’s vesicles. Foissner (1998b) thus argues that loxodids and kentrophorids are sister taxa. We remain skeptical until ultrastructural homologies of the kinetids are proved or until gene sequence data confirm these two groups as sister taxa.
