Control of Flowering by Phloem Exudate from Cotyledons of Ipomoea tricolor II. Low Molecular Weight Flower-inhibiting Substance(s)

The phloem exudate prepared from the cotyledons of Ipomoea tricolor strain Heavenly Blue seedlings that have been exposed to a single 16 h dark period induced flowering in cultured apices excised from non-induced seedlings. When the phloem exudate was dialyzed and separated to 3 fractions such as low ( (cid:6) 1,000), middle (1,000 (cid:1) 10,000), and high ( (cid:7) 10,000) molecular weight, both low and high molecular weight fractions had flower-inducing activities, but not middle fraction. The low molecular weight fraction was further separated and examined the nature of flower-inducing substance(s). The substance(s) was heat-stable and the highest rate of floral bud induction was obtained with 3 (cid:1) g freeze dry weight mL (cid:8) 1 . From the results of solvent participation and ion exchange chromatography, the substance(s) was high polar, seemed to be acidic, and the flower-inducing activity only increased from 3- to 10-fold.