Regulation by Abscisic Acid of In Vitro Flower Formation in Torenia Stem Segments

In Torenia stem segments cultured on a defined medium withoutphytohormones, in vitro flower formation was influenced by thephysiological states of the explants. Endogenous contents ofABA, but not those of IAA, were closely correlated with thephysiological states of the explants. Application of ABA (100ng/ml) to the culture medium stimulated flower formation inthe originally vegetative explants which otherwise had littleflower-forming capacity. Thus, endogenous ABA seems to be oneof the factors controlling the flower-forming capacity of Toreniastem segments. The highest rate of flower formation in the stemsegments was obtained when endogenous contents of ABA (whichresulted from both endogenously present and externally appliedABA) in the stem tissues was between 16 and 20 ng/g fresh weight. ¹ Present address: Bioscience Research Center, Mitsui PetrochemicalIndustries Ltd., Waki-cho, Kuga-gun, Yamaguchi 740, Japan. (Received November 22, 1984; Accepted March 1, 1985)