Meiosis in Coprinus: IX. the influence of premeiotic s-phase arrest and cold temperature on the meiotic cell cycle

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Abstract
Arrest of premeiotic 5 phase by high temperature and light causes the meiotic cell cycle time to become shortened by 4 h after release of the arrest. Genetical and cytological evidence shows that diplotene is drastically reduced from 4·5 h to less than 1 h. Cycloheximide (50 μg/ml) treatment of early and late diplotene cells in normal cultures prevents the meiotic divisions even though the chromosomes are condensed. The same treatment given within 1 h of metaphase I allows both divisions to be completed but fails to allow sporulation. This is interpreted to mean that the cellular programme for meiotic division (division programme) is made during diplotene. In the arrest-release cultures, however, the division programme is made during pachytene. This finding is interpreted to mean that the cellular programme in meiosis is prepared one step at a time. When the nuclear cycle is arrested, the cytoplasmic programmes continue. As a result, the division programme is precociously induced at pachytene. Since the diplotene programme is complete, the cells proceed directly from pachytene into metaphase I with the diplotene stage drastically reduced. Cold treatment at 5 °C at pachytene temporarily suspends the progress of meiosis and hence prolongs the pachytene stage. This prolongation causes an increase in recombination frequency. This finding supports the argument that recombination frequency is a function of time.