Kaempferol 3-O-Galactoside, 7-O-Rhamnoside is the Major Green Fluorescing Compound in the Epidermis of Vicia faba

Abstract

The vacuoles of lower epidermal strips from V. faba exhibit an intrinsic green fluorescence when incubated in alkaline buffers. Using an alkaline-induced absorbance change as a spectrophotometric assay, the major pigment responsible for this fluorescence was isolated and identified as the flavonoid, kaempferol 3-O-galactoside, 7-O-rhamnoside. The aqueous absorption maxima were 394 and 341 nm at pH 10.0 and 6.0, respectively, with a pKa [dissociation constant] of 8.3 and the fluorescence emission maximum was 494 nm at pH 10.0. The in vivo concentration was estimated to be between 3 and 10 .mu.M. The absorption spectrum of this flavonoid is different from the action spectrum for stomatal opening, indicating that this compound is not the photoreceptor pigment for the blue light response of V. faba guard cells.