Sporulation competence in Physarum polycephalum CL and the requirement for DNA replication and mitosis

The optimum conditions for sporulation and the requirements for mitosis and DNA replication during the onset of the process have been investigated in plasmodia of the CL strain of Physarum polycephalum. A 72 h period of starvation was necessary before a plasmodium became competent to sporulate on exposure to light. The plasmodium became irreversibly committed to sporulation 4 to 5 h after illumination. The commitment point was related to the time of illumination rather than the duration of starvation. Three periods of DNA synthesis were detected during the initial 24 h of starvation, but in an asporogenous derivative of the CL strain only the first two periods were detected. Inhibition of mitosis with nocodazole or of DNA synthesis with hydroxyurea prevented sporulation. Escape of plasmodia from hydroxyurea inhibition of sporulation coincided with the last detectable period of DNA synthesis, but escape from nocodazole inhibition of sporulation occurred 25 to 30 h later.