Organ Regeneration in Sterile Culture After Median Bisection of the Flower Primordia of Nicotiana tabacum

Tobacco flower apices at different developmental stages were bisected and cultured in vitro. Floral organs regenerated next to the cut and the type of response was related to the initial stage of the bud Up to and including the primordial sepal stage, petal and stamen primordia usually regenerated at least in one half and pistil primoidia in both halves At the primordial petal stage, only pistil regeneration occurred. Finally, all regenerative capacity was lost at the primordial carpel stage. The data support the view that the developing flower passes through a series of physiological phases which govern the sequential appearance of the floral organs. Under the experimental conditions, the normal sequence of organ initiation is not easily reversed or disrupted and so it appears committed to progress in one direction The technique resolves relatively distinct sepal- and carpel-forming phases but only one phase seems to govern the initiation of both petals and stamens The bud center was usually much more responsive to surgery than the meristem flanks. On this basis, it is suggested that changes in this central region during floral ontogeny may regulate organogenic events on the periphery of the meristem