Les critères cytophysiologiques de la phase intermédiaire chez l’Aster sinensis (Composées)

Abstract

Aster sinensis flowering normally occurs under 12-h- or 8-h-long days. However, in this species, the transition to the prefloral stage is accelerated by long days, while the floral morphogenesis is favoured by a 12- or 8-h day length. Under short or 12-h photoperiods, the plants go through a long intermediate phase during which the plastochrone has a duration equal to that observed in the preceding vegetative phase. During the intermediate phase, the sizes of all apical zones noticeably increase, particularly for the axial zone, at the corpus level. Moreover, mitotic indices and DNA contents in all zones are significantly higher than those of vegetative meristems. In the shoot apex of Aster sinensis, the intermediate phase, which involves structural and nuclear changes, appears as a preparatory stage to flowering.