Analysis of epicuticular phenolics of Prunus persica and Olea europaea leaves: Evidence for the chemical origin of the UV-induced blue fluorescence of stomata

Epicuticular waxes were removed from the leaf surfaces of Olea europaea and Prunus persica by washing with chloroform and the resulting rinses were an alysed by high performance liquid chromatography (HPLC) for the presence of fluorescing compounds. Removal of epicuticular waxes from leaves of some r epresentative plants by the same treatment resulted in a significant reduct ion in the intensity of the blue fluorescence emitted from guard cells (Kar abourniotis et al., 2001: Annals of Botany 87. 631-639). Ferulic acid and p -coumaric acid, as well as a number of unidentified compounds, were constit uents of the rinses of both plants examined but only after alkaline hydroly sis of the samples. This indicates that both phenolic acids are tightly bou nd to the epicuticular waxes of the leaves of these plants. HPLC chromatogr ams of rinses derived either from the abaxial or adaxial surfaces of the hy postomatic leaves of O. europaea did not show significant qualitative diffe rences. Nevertheless, ferulic acid (the main blue fluorescent component) wa s much more abundant in the abaxial than the adaxial surface. In P. persica , the composition of the sample derived from the abaxial surface was far mo re complex, and all constituents were present in much higher concentrations than in the sample derived from the adaxial surface. Given the particular fluorescence characteristics of ferulic acid, the differences in its concen tration between abaxial and adaxial surfaces. and between the two species, and the fluorescence images of these surfaces under the microscope, we prop ose that this compound is probably the main epicuticular constituent respon sible for the blue fluorescence emitted by guard cells of the species exami ned. The functional significance of the findings is discussed. (C) 2001 Ann als of Botany Company.