Determination of Cell Cycle and DNA Synthesis Duration in the Shoot Apex of Chrysanthemum segetum L. by Double-labelling Autoradiographic Techniques

Abstract

The duration of the cell cycle and the DNA synthetic phase were estimated in various zones of the shoot apex of Chrysanthemum segetum according to two different double labelling techniques. In plants growing in a 16-hour photoperiod on which the sixth leaf had been initiated, the cell cycle duration was about 130 hours in the axial zone, 50 hours in the lateral zone and 70 hours in the rib meristem. The mean duration of the synthetic phase, which was between 7.7 and 10.3 hours according to the zone, did not increase in proportion to a lengthening of the cycle either in the axial zone or in the rib meristem. These findings are discussed in relation to the estimation of the DNA content in various zones as obtained by cytophotometric measurements. They support the hypothesis of a particular lengthening of the duration of the G 1 phase in the axial zone, where the cycle is in fact most prolonged.