Zada-Hames I M, Ashworth J M
J Cell Sci. 1978 Aug;32:1-20. doi: 10.1242/jcs.32.1.1.
The cell cycle in amoebae of Dictyostelium discoideum has been analysed in cells growing asynchronously in axenic medium. For cells growing at the optimum growth temperature of 22 degrees C with a culture doubling time of 8 h the average times for the cell cycle phases are as follows: G1, 1.5 h; S, 2.1 h; G2, 4.4 h; M, 15.2 min. When amoebae are grown at temperatures below 22 degrees C, culture doubling time increases and the cell cycle phases are altered in ways characteristic for each phase. G2 is the most variable period and may occupy up to 70% of the total cell cycle time; S and G1 are the least affected, increasing by only 20% when the cell generation time is doubled. When cells which have reached the stationary phase of growth in liquid medium are washed and reinoculated into fresh medium they divide synchronously after a lag period of 5 h. By following cell number increase and nuclear DNA synthesis in these cultures we have shown that stationary phase cells are arrested in the G2 phase of the cell cycle. Finally, although more than 97% of amoebae grown on a bacterial food source are uninucleate, when grown axenically up to 35% of the cell population may become multinucleate. Our results suggest that these cells probably arise through the failure of cytokinesis to follow karyokinesis. Multinucleate cells appear to have a slightly longer G2 period than mononucleate cells.
在无菌培养基中异步生长的盘基网柄菌变形虫的细胞周期已得到分析。对于在22℃最佳生长温度下生长、培养倍增时间为8小时的细胞，细胞周期各阶段的平均时间如下：G1期，1.5小时；S期，2.1小时；G2期，4.4小时；M期，15.2分钟。当变形虫在低于22℃的温度下生长时，培养倍增时间增加，且细胞周期各阶段以每个阶段特有的方式发生改变。G2期是变化最大的时期，可能占据细胞周期总时间的70%；S期和G1期受影响最小，当细胞世代时间加倍时仅增加20%。当在液体培养基中达到生长静止期的细胞被洗涤并重新接种到新鲜培养基中时，它们在5小时的延迟期后同步分裂。通过跟踪这些培养物中细胞数量的增加和核DNA合成，我们表明静止期细胞停滞在细胞周期的G2期。最后，尽管在细菌食物源上生长的变形虫中超过97%是单核的，但在无菌条件下生长时，多达35%的细胞群体可能会变成多核。我们的结果表明，这些细胞可能是由于胞质分裂未能跟随核分裂而产生的。多核细胞的G2期似乎比单核细胞略长。
