A phase-dependent delay of the chick pineal rhythm in rate of thymidine incorporation by brief exposure to aphidicolin.

Cultured chick pineal glands show a persistent rhythm in the rate of cumulative incorporation of thymidine into DNA. In this study we have examined the effects of pulse-exposure to aphidicolin in the dark on the first day of culture on thymidine incorporation during the second and third days of culture in the dark with aphidicolin-free medium. The phase of the rhythm in the rate of thymidine incorporation was delayed in a concentration-dependent manner by a 4-hr exposure to aphidicolin, commencing in the final hour of the photoperiod. This effect was phase-dependent and not seen when exposure to aphidicolin began earlier in the photoperiod.