Abstract
The flower-inhibiting activity of phloem exudate prepared from cotyledons of Ipomoea tricolor strain Heavenly Blue seedlings cultivated to continuous light conditions was examined, using apex cultures in vitro as a bioassay system. The phloem exudate inhibited flowering in apices excised from seedlings exposed to a single 16 h dark period to induce flowering. When the phloem exudate was dialyzed and separated to 3 fractions such as low (‹1,000), middle (1,000–10,000) and high (›10,000) molecular weight, low molecular weight fraction had flower-inhibiting activity, but not middle and high molecular weight fractions. The low molecular weight fraction was separated and examined the nature of the flower-inhibiting substance(s). The flower-inhibiting activity appeared to be heat-stable. The low molecular weight fraction was extracted by CHCl 3 and ethyl acetate. The fraction with activity from solvent participation was further fractionated by ion-exchange chromatography. The active fractions were applied to a Sep-Pak C18 cartridge. From the results of fractionation, the flower-inhibiting substance(s) was low molecular weight, high polar, seemed to be basic, and the flower-inhibiting activity was increased about 10-fold.
