The different phases of development of the apical meristem in two ecotypes of Arabidopsis thaliana (L.) Heynh. [one French (a quantitative long‐day plant), the other one Swedish (an absolutely cond‐requiring plant)] were established, under conditions either inductive or not inductive of flowering. Then the effects of gibberellins (GA3, GA4/7) and cytokinin (6‐BA) on these ecotypes were studied at different stages of their ontogenic development. The rate of plant growth was estimated by measuring the plastochron duration. The activities of the different apical zones were determined with cytochemical methods and by histoautoradiography after incorporation of 3H‐thymidine into DNA. When treated during the vegetative stage, i.e. at a young age (French ecotype) or in absence of cold treatment (Swedish ecotype) flowering was not induced. The tested chemicals had similar effects: at first a stimulation of the phylogenetic activity of the cells of the lateral zone and of the rib meristem and, after extended treatments, a differentiation of the axial cells of the meristem and, as a result, an inhibition of flowering. On the other hand, the different hormonal applications on meristems which have reached the intermediate stage, were effective in inducing the reproductive state. The activity of the central cells already in the process of dedifferentiation was increased and, by this, flowering was promoted.
Besnard -Wibaut, C, Cochet, T. and Noin, M. 1989. Photoperiod and gihberellic acid -control of the cell cycle in the meristem of Silene armeria and its effects on flowering. Plants of Silene armeria L., strain S,.], a quantitative long-day (LD) species which is known to react tO' GA3 by flowering after attaining the 'intermediate stage', were induced by two LD or by two GA3 applications. Changes in the mitotic index and DNA content (microdensitometric estimation) of cells in the axial zone, lateral zone and rib meristem of the shoot apex were observed during the first 48 h of each treatment. Similar mitotic activation occurred in response to LD or GAj after a 6-8 h lag period. This was preceded by a decrease in the proportion of nuclei with a 2C DNA content, indicating that in this species the control point for the shortening of the cell cycle was essentially in Gj. A second mitotic peak was observed 16 h later in photoinduced meristems, resulting in more pronounced cellular synchronization. These further events were not seen in GAj-treated plants where only the meristematic activity was slightly, but reproducihiy higher than in the control. Thus, two successive synchronizations of cell division are a typical feature of LD induction. The data are discussed with regard to the competence of shoot apical cells to be reactivated. The essential changes for tfie transition to flowering depend on these differential pattems of cell reactivation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.