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

Abstract

The vacuoles of lower epidermal strips from Vicia 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 nanometers at pH 10.0 and 6.0, respectively, with a pKa of 8.3 and the fluorescence emission maximum was 494 nanometers at pH 10.0. The in vivo concentration was estimated to be between 3 and 10 micromolar. 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 Vicia faba guard cells.