Cytokinin as a Possible Component of the Floral Stimulus in Sinapis alba

Results of previous investigations indicated that one of the early and essential events occurring in the apical meristem of Sinapis alba L. during the transition to flowering is the release to mitosis of the G(2) nuclei; the trigger to mitosis is generated in the leaves and its movement out of the leaves begins around 16 hours after the start of the inductive treatment. The mitotic wave in the meristem culminates 10 hours later.In this paper, it is shown that a single application of a cytokinin (benzyladenine or zeatin) at concentrations ranging from 1 to 20 mug/ml directly to the apical bud of vegetative plants, at a time corresponding to the time of movement of the mitotic trigger in induced plants, produces a mitotic wave which is very similar to that found in induced plants. It is thus proposed that the mitotic component of the floral stimulus in Sinapis is a cytokinin. As the cytokinins are completely unable to induce flowering, it appears that there is a multicomponent floral stimulus in this species.