REGULATION OF CORTICOTYPE THROUGH KINETY INSERTION IN TETRAHYMENA

Insertion of a new ciliary row (kinety) has been documented in cells of Tetrahymena thermophila subjected to certain nutritional shift‐down conditions. Under these conditions cells replace their oral structures and become rapid‐swimming, dispersal forms. During the oral replacement process cells with 18 or 19 kineties frequently add a kinety to express a corticotype (kinety number) of 19 or 20. Cells of corticotypes 20 or 21 do not change corticotype under these conditions. When cells undergo oral replacement upon entering stationary phase in nutrient medium, no increase in corticotype takes place even when the initial corticotype is 18 or 19. The increase in corticotype thus depends on the occurrence of oral replacement, the initial corticotype, and the nutritional shift‐down. Examination of cells stained with protein‐silver indicates that a new kinety is inserted near the conclusion of the oral replacement process in a postoral position, between the two pre‐existing postoral kineties (1 and n). The process appears to involve the insertion of basal body couplets derived from the newlyformed undulating membrane. This process forms a third postoral kinety. One of the original postoral kineties (n) is eventually extended to the anterior end of the cell to the left of the new oral apparatus. The present findings suggest that cortical stability characteristics are likely to be different under natural conditions, which are likely to involve periodic starvation, than they are under continuous cultivation in axenic nutrient media in the laboratory. It is predicted that under natural conditions a unique stability center near corticotype 20 will be manifested. Copyright © 1979 Wiley‐Liss, Inc., A Wiley Company