In vivo-Microspectrophotometric Characterization of Flavonol Glycosides inVicia fabaGuard and Epidermal Cells

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Abstract
Cytological observations by fluorescence and U.V.-absorption microscopy together with in vivo spectrophotometric analyses of stomata, guard cell protoplasts and epidermal cells of Vicia faba have shown that kaempferol 3,7-O-glycosides are localized in the vacuoles. The alkaline-induced emission spectra recorded with guard and epidermal cells after NH4OH-treatment were identical, exhibiting an emission maximum at 525 nm; the spectra correlated with that of reference flavonols after exposure to NH4OH The excitation spectra of both cell types are typical of these flavonols showing two maxima at 290 nm and 390 nm. In agreement, two absorption maxima were recorded for guard cells at 270 nm and 330 nm, without alkali, which shifted bathochromically to 275 nm and 380 nm, respectively, after NH4OH treatment. The fluorescence intensity measured at 525 nm demonstrates a photostability in epidermal cells whereas it increases by a factor of about five with the excitation time up to 30 min in guard cells. For the latter, several possible processes are discussed.