Plastochrone, cycle cellulaire et teneurs en ADN nucléaire du méristème caulinaire de plants de Chrysanthemum segetum soumis à deux conditions lumineuses différentes, sous une photopériode de 16 heures

Abstract

Chrysanthemum segetum plants were grown from seeds under a 16-h photoperiod, at two different photon fluence rates (70 or 200 μmol m−2 s−1. At 200 μmol m−2 s−1, by comparison with 70 μmol m−2 s−1, phyllotaxy was not modified, but the plastochron decreased and the apical diameter increased by extension of the axial zone. The mean cell doubling time decreased 36.2% in the lateral zone, 29% in the axial zone, and only 13% in the rib meristem. In contrast, mitosis duration was constant. Under both light conditions, nuclei with a DNA content within the limits of the 2C range were always predominant, which means that the G1 phase of the cell cycle was the longest. At 200 μmol m−2 s−1, the shortening of the mean cell doubling time is accompanied by a reduction of the percentage of nuclei with DNA levels within the limits of the 2C range. The decrease of the latter was the most important in the axial zone and the least important in the rib meristem, showing that control of cell proliferation was obtained by means of the G1 phase of the cell cycle. Key words: Chrysanthemum segetum, cell cycle, duration of mitosis, plastochron, nuclear DNA levels, zonation.