Flowering may be controlled by a quantitative balance between flower-inducing and -inhibiting substances in Pharbitis nil

Phloem exudate prepared from induced cotyledons of Pharbitis nil (SD-PE) showed flower-inducing activity, and the exudate from cotyledons of P. nil grown under continuous illumination (CL-PE) expressed flower-inhibiting activity in apex cultures of P. nil. Following fractionation by ion exchange chromatography, the flower-inducing activity of SD-PE was located in the fraction adsorbed on anion exchange resin (Dowex); the flow-through (FT) fraction from anion and/or cation exchange resins used to separate CL-PE inhibited flowering. The flower-inducing and -inhibiting activities of both fractions from SD-PE and CL-PE were examined in detail. The FT fraction of SD-PE inhibited, and the Dowex fraction of CL-PE induced flowering. The flower-inducing activity of Dowex fraction of SD-PE was about 100 times higher than the same fraction of CL-PE, and the inhibiting activity of FT fraction of CL-PE was about 10 times higher than the same fraction of SD-PE. Therefore, flowering in P. nil may be controlled by a quantitative balance between flower-inducing and -inhibiting substances.