No abstract

In this study a method was designed to assess non-destructively the type of UV-screening compounds present in the leaf epidermis. The method is based on the recording and calculation of the ratio of UV-excitation spectra of chlorophyll fluorescence (FER) from the adaxial and abaxial sides of bifacial leaves, or from older and younger segments of monocotyledonous leaves. The logarithm of this ratio (logFER) matched the absorption spectrum of the UVabsorbers present in the leaf, as confirmed by its overlap with the absorption spectrum of the methanolic extract of the leaf or of the isolated epidermis. By using the logFER approach, it was possible to demonstrate that the concentration but not the classes of compounds present in the epidermis that are responsible for UV-screening is affected by the side and the age of the leaves. In contrast, measurements from the leaves of seven dicots and one monocot indicated large difference in the classes of these compounds between species. Finally, it was shown that the logFER in the UV is independent of the emission wavelength, and that the method can be used for quantitative measurements. This method expands to the spectral domain the use of ChlF for the estimation of the leaf epidermal transmittance.

Dualex (dual excitation) is a field-portable instrument, hereby described, for the assessment of polyphenolic compounds in leaves from the measurement of UV absorbance of the leaf epidermis by double excitation of chlorophyll fluorescence. The instrument takes advantage of a feedback loop that equalizes the fluorescence level induced by a reference red light to the UV-light-induced fluorescence level. This allows quick measurement from attached leaves even under field conditions. The use of light-emitting diodes and of a leaf-clip configuration makes Dualex a user-friendly instrument with potential applications in ecophysiological research, light climate analysis, agriculture, forestry, horticulture, pest management, selection of medicinal plants, and wherever accumulation of leaf polyphenolics is involved in plant responses to the environment.