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Cap 5

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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.

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