G1-phase arrest is not a prerequisite for encystment in Physarum.
Amoebae of the Myxomycete Physarum polycephalum form resistant, walled cysts when the food bacteria in a culture have been consumed. No G1 phase has been detected in the vegetative amoebal cell cycle, most of which comprises the G2 phase. Mature cysts are also in G2, but it has been reported that a G1 phase of roughly 24 h, followed by an S phase, is obligatory prior to encystment. We used flow cytometry to determine the distribution of DNA contents in amoebal cultures at intervals during vegetative growth and encystment. In all cultures, the cells were predominantly in G2 phase, and the percentage of cells with G1 DNA content remained very low. We conclude that an extended G1 phase of 24 h did not occur in our cultures and cannot be a prerequisite for encystment.
Anderson
R W
RW
Department of Molecular Biology and Biotechnology, University of Sheffield, United Kingdom. r.anderson@sheffield.ac.uk
Dee
J
J
Foxon
J L
JL
D000818:Animals; D002455:Cell Division / Q000502:physiology; D005434:Flow Cytometry; D016193:G1 Phase / Q000502:physiology*; D016839:Physarum polycephalum / Q000166:cytology* / Q000254:growth & development*