Time-resolved blue-green fluorescence of artichoke leaves

Artichoke leaves emitte blue-green fluorescence (BGF) under ultraviolet (UV) excitation. The abaxial (lower) side was several-fold more fluorescent than the adaxial (upper) side and, in both cases, the youngest leaves were much more fluorescent than the oldest ones. Our data indicate that a fraction of the BGF of artichoke leaves is due to the presence of hydroxycinnamic acids. Preliminary results suggest that chlorogenic acid may be the main fluorophore in artichoke leaves, although cynarin and caffeic acid may also contribute in the case of young leaves. We have detected all of them by mass spectrometry in artichoke leaves. Data from time-resolved leaf BGF, leaf BGF excitation spectra and UV absorption spectra of the leaf methanolic extracts revealed a loss of hydroxycinnamic acid derivatives with the age of the leaf, although senescent leaves had still concentrations several-fold higher than those found in many other species. Microscopic observations demonstrated that a large part of the artichoke leaf BGF arose from trichomes of the epidermal layer and from the cuticle.