The Effect of Nocodazole on Cell Cycle Events in the Plasmodial Slime Mould Physarum Polycephalum

The action of nocodazole on nuclear morphology, DNA replication and thymidine (TdR) kinase activity has been examined in growing and starving plasmodia of the CL strain of Physarum polycephalum. In the growing plasmodium, nocodazole treatment more than 2 h before mitosis began prevented both mitosis and DNA replication from occurring at the normal time and also prevented the increase in TdR kinase specific activity normally associated with the onset of mitosis. Nocodazole treatment less than 2 h before mitosis began allowed the process to begin at the normal time, but it was not completed. A normal increase in TdR kinase specific activity accompanied the abortive mitosis, but only limited DNA replication was detected. A similar effect of nocodazole on the occurrence of DNA synthesis in starving plasmodia was found. Nocodazole treatment of a starved plasmodium re-fed with growth medium indicated that the plasmodium was in the G2 phase of the cell cycle when it became competent to sporulate.