Axillary bud inhibition induced by young leaves or bract in Euphorbia pulcherrima willd

In plants held under long days in the vegetative stage, young expanding leaves of poinsettia (Euphorbia pulcherrima Willd. 'Brilliant Diamond') are the main source of axillary bud inhibition, while the apical bud, which includes the meristem, primordial leaves and small unfolded leaves, is a secondary inhibition source. Removal of these expanding leaves resulted in rapid release and growth of axillary buds. Decapitation of the apical bud resulted in delayed axillary bud release. In reproductive plants kept in short days, the pigmented bracts are the primary source of axillary bud inhibition and the cyathia are the secondary source. Applications of NAA -substituted for both young leaves and bract inhibition - maintained apical dominance. The concentration of endogenous auxin was highest in the apical bud. However, when calculated on whole organ basis the auxin level was greater in young developing vegetative leaves and in reproductive bracts than in the apical bud.