Cytoplasmic membrane changes in conjugating Tetrahymena

Summary The formation of stacks of smooth-surfaced cisternae was studied in samples of Tetrahymena pyriformis that were prepared for electron microscopy after starvation for 2 days in buffer, and in samples of organisms of different mating type that were starved for 2 days and then mixed to induce conjugation. The number of stacks of cisternae was greater in starved ciliates than in those from stock cultures, and the size and number of stacks increased further after mixing animals of different mating type. When cells were either starved or mixed in buffer to which the protein synthesis inhibitor cycloheximide had been added, the formation of the membranous stacks was almost completely abolished. Addition of the RNA synthesis inhibitor actinomycin D, however, did not result in a significant decrease in the size and number of the stacks of saccules. Conjugation did not occur in the presence of either cycloheximide or actinomycin. The results suggest that protein synthesis is required for the formation of the stacks, but RNA synthesis is no longer necessary for their formation at this stage. The previous identification of the stacks as a Golgi apparatus and the possible functions of these membranes are considered.Supported by grants from NSF (GB-32285) and the American Cancer Society (E-500).The authors acknowledge the technical assistance of Mrs. Sue Thompson.