The cell cycle in vegetative and floral shoot meristems measured by a double labelling technique.

A double labelling technique was used to measure the length of the cell cycle in the shoot apical meristem of Silene coeli-rosa L. plants kept in short days, in which they remained vegetative, or exposed to 7 long days, which induced flowering. The length of the cell cycle in the vegetative plants (those in short days throughout) was about 18 hrs. It was also 18 hrs, or somewhat longer, in plants which had been exposed to long-day conditions for 5 days, by which time 90% of the plants are committed to flower. When plants had been exposed to the full inductive period of 7 long days and had been transferred back again to non-inductive (short day) conditions, floral morphogenesis had just begun and the cell cycle had almost halved, to 10 hrs. The cell cycle was therefore unaltered during floral induction and shortened only at the onset of the growth of the flower itself.