MACRONUCLEAR ENVELOPE OF TETRAHYMENA PYRIFORMIS GL IN DIFFERENT PHYSIOLOGICAL STATES .2. FREQUENCY OF CENTRAL GRANULES IN PORES

Macronuclear envelopes were isolated from the ciliated protozoan Tetrahymena pyriformis GL, negatively stained and examined in the electron microscope. The frequency of central granules in the macronuclear pores was evaluated in five different physiological states: (1) stationary phase of growth, (2) exponential phase of growth, (3) heat-synchronized cultures at the end of the heat-synchronization treatment, (4) heat-synchronized cultures at the beginning of the first division, (5) heat-synchronized cultures at the end of the first division. The percentage of pores containing a central granule was markedly enhanced in heatsynchronized cultures at the end of the first division, i.e. a state known for an increase in ribosome formation. Actinomycin D was found to cause a significant decrease in central granule frequency. The observed alterations in central granule frequency seem to confirm the hypotheses which consider the central granule as representing a ribonucleoprotein particle in transit from nucleus to cytoplasm through the nuclear pore. © 1969 Springer-Verlag.