Morphogenetic events in normal and synchronously dividing Tetrahymena.

SYNCHRONOUS cell-division has been induced in mass cultures of the small ciliated protozoan Tetrahymena pyriformis (Scherbaum & Zeuthen, 1954). While it is known that cells grow in a characteristic way during the synchronizing treatment the effect on the morphogenetic events associated with the cell cycle is not clear. Studies in ciliate morphogenesis generally have established the central position of the ciliary basal body, or kinetosome, in developmental processes. The kinetosomes are believed to be self-duplicating structures, the kinetosomal population of a daughter cell arising directly by kinetosomal reproduction in the parent cell. The species-specific pattern of the ectoplasmic cortex is largely a matter of the distribution of kinetosomes. Further, the kinetosomes appear to function either as building blocks or 'local organizers' in most, if not all, structural syntheses occurring in the cortex, i.e. in the production cilia, cirri, membranelles, trichocysts, and other ciliate structures (see Weisz, 1954). Two conflicting notes are available concerning the behaviour of kinetosomes and kinetosomal derivatives in synchronized cultures of Tetrahymena. Child (1957) has reported that kinetosome reproduction continues and new mouth parts are formed in cultures of T. pyriformis W subjected to the synchronizing treatment. On the other hand, Holz, Scherbaum, & Williams (1957) have reported that formation of mouth parts and also mitosis is inhibited by the synchronizing treatment in T. pyriformis WH-6 (mating type I, variety 1). In the present study kinetosomes and kinetosomal derivatives in T. pyriformis GL were studied in detail in order to elucidate the relation of the morphogenetic events of the cell cycle to the experimentally induced synchronous cell-division. On an earlier occasion cell-growth in synchronized cultures was studied (Scherbaum, 1956). The mean cell size was found to increase from threeto fourfold as a result of the treatment. When the cells were grouped in logarithmic size