Ultrastructural aspect of size dependent regulation of surface pattern of complex ciliary organelle in a protozoan ciliate.

A regulation is shown for size and number of the elements of complex ciliary structures forming the oral apparatus (OA) of a ciliate Paraurostyla weissei. Morphometric investigations were performed on oral ciliature of normal and size-reduced cells. Those constituents of the OA which exist as single structures, such as the inner and outer preoral membranelles, are not eliminated. Both shorten and the outer membranelle becomes narrower. Within the adornal zone of membranelles in size-reduced cells some frontal and ventral membranelles become eliminated, whereas the respective ratio of these types remain size invariant. In each individual adoral zone of membranelles there are membranelles of different length specifically located along the ventral part. Membranelles from small cells are significantly smaller than those of normal cells. The number of kinetosomes is reduced in all four rows constructing an adoral membranelle. The analysis showed that regardless of cell size, the number of kinetosomes in the two inner rows of a membranelle is linearly and proportionately related. Regulation of the size of all components of the oral ciliature in P. weissei occurs at the time when the primordia of oral ciliature are formed. The results are discussed in relation to recent ideas about pattern formation and size dependent regulation of the number and size of pattern elements.