Morphogenesis and Division in Chains of Tetrahymena pyriformis GL*

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Abstract
SYNOPSIS. The formation of chains was induced both in exponentially growing and in synchronized cultures of Tetrahymena Pyriformis GL, by application of one or two hr 34°C shocks. An arrest in constriction along the division furrow is brought about as a result of prolonged exposure to 34° during an early phase of cell division.After return to optimal temperatures, the chains remain in their original tandem configuration. They possess two sets of cortical structures, and generally also two macronuclei.Subsequently, two new oral primordia appear, one in each component. These primordia develop in synchrony with each other. The later development of the chains is correlated with the placement of the oral primordia. In some situations, these primordia form immediately posterior to the pre‐existing oral areas and replace them; in these cases, the original division furrow is obliterated, and irregular and probably unstable homopolar doublets form. More frequently, one or both of the oral primordia are normal division primordia. In these cases, the original oral area of the anterior component persists, while that of the posterior component is resorbed. The original fission line persists, and two new fission lines are formed anterior to each of the new oral primordia. When constriction takes place along the new fission lines, the original arrested fission line is occasionally reactivated, and the chain then divides into four cells. More often, the original furrow is not reactivated (or only incompletely reactivated), and the chain divides into two or three cells, depending on how close the two new division furrows are to each other.The chains ultimately give rise to normal clones of singlet cells. No clones of doublets were observed.In the Discussion, the synchronization of developmental events in the two components of the chain is emphasized. The cases of reactivation of the original fission line in synchrony with constriction along the newly formed fission lines seem to indicate that furrowing results from an interaction of a preformed cortical site (fission line) with a pervasive substance which acts to trigger constriction.