Effectiveness of gibberellins and 6‐benzyladenine on flowering of Arabidopsis thaliana

Abstract

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.

The pleiotropic effects induced by therolC gene in transgenic plants are caused by expression restricted to protophloem and companion cells

“…A similar stimulation of radial growth of pith and parenchyma cells was observed after exogenous treatment with cytokinins (Brossard, 1976;Besnard-Wibaut, 1981). In in vitro culture, cytokinins.also act as modulators for leaf shapes, as indicated by the observation that 2 • 10-5M kinetin and BAP led to lanceolated leaves (Iskander, 1980).…”

A novel cytokinin-resistant mutant of Arabidopsis with abbreviated shoot development

“…However, in Arabidopsis stimulation of flowering by exogenous cytokinin is dependent on the developmental stage of the meristem and is possible only in plants having meristems at an "intermediate" stage, not those at a young "vegetative" stage (Besnard-Wibaut 1981). In tobacco thin-cell-layer cultures, high concentrations of cytokinin inhibit flower formation and promote the production of vegetative buds, although lower concentrations of cytokinin are required for flowering (Tran Thanh Van 1980).…”

Le méristème caulinaire des Angiospermes: nouveaux outils, nouvelles interprétations

“…Des travaux recents (Finnegan eta/., 1998 ;Dennis eta/., 2000) ont montre que Ia methylation des residus cytosine du DNA ferait partie des mecanlsmes assurant un controle genique, en particulier pour les plantes qui ont besoin de froid pour fleurir, comme certains ecotypes d'Arabidopsis thaliana. Les (Besnard-Wibaut, 1966, 1981 La phase intermediaire, dont ! 'acquisition pourrait correspondre a une induction partielle (Bernier, 1988), revet une importance considerable.…”

“…On suppose (Schneeberger et a/., 1998) Les plus jeunes feuilles envoient des messages au meristeme sous forme de metabolites et de substances de croissance. Si auxine et cytokinine interviennent, elles le font, vraisemblablement, differemment suivant l'etat hormonal endogene du meristeme qu'elles atteignent (Maksymowych & Erickson, 1977 ;Mauseth, 1979 ;Besnard-Wibaut, 1981 ;Nougarede & Rembur, 1985 ;Niebla Hernandez & Driss-Ecole, 1990a et b). Les plus jeunes feuilles envoient aussi au meristeme des informations sur Ia position des derniers organes formes.…”