Nuclear-Cycle Dependence of the Development of the Preprophase Band in Tobacco BY-2 Cells

When tobacco BY-2 cells that had been treated with aphidicolinfor 24 h were cultured in the absence of aphidicolin, DNA synthesiswas initiated within 1 h. DNA synthesis was completed within4 h and then the preprophase band of microtubules (PPB) developed.However, when cells that had been treated with aphidicolin werecultured in the absence of aphidicolin for 1 h and then againin its presence, DNA synthesis, which was initiated during thehour in the absence of aphidicolin, was not completed withina further 10 h in the presence of aphidicolin. Moreover, thePPB did not develop even after the PPB had appeared and disappearedin cells that were cultured contemporaneously in the continuedabsence of aphidicolin. The development of the PPB seems to be causally associated withthe nuclear cycle of cell division in tobacco BY-2 cells. Thisprocess seems to require the completion of the replication ofall, or almost all, of the nuclear DNA. (Received July 25, 1992; Accepted November 24, 1992)