Regulation of the pattern of basal bodies within the oral apparatus of Tetrahymena thermophila.

The number and arrangement of basal bodies included in the four compound ciliary organelles making up the mature oral apparatus of Tetrahymena thermophila ordinarily vary only slightly. Severe starvation brings about formation of oral structures with a reduced number of basal bodies within these organelles, and sometimes with a complete loss of one of the component organelles. Such reductions are stringently specified in spatial terms, but they do not represent simple and proportional shrinkage of the organelle complex. Instead, certain spatial features remain essentially unaltered, while others undergo major quantitative reductions, resulting in large changes in the internal proportions of the structures. This selective regulation can be explained in terms of the different parallel and sequential processes taking place during the development of this organelle complex. There is also no strict proportionality between the size of the oral apparatus and that of the cell; instead, oral apparatuses become relatively larger as cells become smaller. This is due in part to the inherent temporal discontinuity of oral development, but there is probably also a real change in the oral/body size relation at the time of oral development. The 'French flag' rule fails when applied to the relative sizes and internal proportions of organelle systems in this and in other ciliates.