Delay in the cleavage of Tetrahymena pyriformis exposed to high hydrostatic pressure

Early cleavage stages of Tetrahymena pyriformis were exposed to 250 atms pressure for periods ranging from 20–200 minutes. Pressure halted cleavage which, in those cells exposed for only a short time, was resumed soon after decompression. Cells exposed to longer periods of pressure treatment failed to resume cleavage soon after decompression but cleaved after a delay approximating to a generation time. In the former case, the cleavage furrow remained intact; whereas in the latter case, the cleavage furrow frequently resorbed and a new furrow was formed to accomplish the delayed cleavage. The results appear consistent with the hypothesis that the hypothetical macro-molecular entity P₂ of Rasmussen and Zeuthen is pressure labile and involved in the mechanical process of cleavage.