Young flower primordia of Nicotiana tabacum 'Wisconsin 38' have been successfully cultured on a nutrient medium supplemented with kinetin. The petal, stamen, and carpel primordia form in the normal acropetal sequence during the first week on excised floral apices which initially bore only sepal primordia. Relatively normal morphogenesis of the organs ensues, and on optimal concentrations of kinetin, pedicel length, calyx length and width, corolla width, and ovary length and width after 4 weeks were comparable to those in the normal flower at anthesis. The corolla, filaments, and style were always much shorter than normal. Large quantities of pollen were produced on low kinetin concentrations and normal embryo sacs formed in the numerous ovules. When kinetin was omitted from the medium, similar explants initiated all the organ primordia, but these subsequently remained minute through 4 weeks of culture. The data indicate that organ initiation is independent of exogenously supplied hormones, but that the later phases of bud growth have a marked requirement for kinetin. It is suggested that the sepals or petals may provide some stimulus for the initiation of meiosis in the anthers and ovules. In that flower morphogenesis in culture is independent of specific regulation from the rest of the plant, bud development appears to be relatively autonomous.
Genetics and functions of the retinoic acid pathway, with special emphasis on the eye