Differences in Fluorescence Excitation Spectra of Leaves between Stressed and Non-Stressed Plants

Abstract

Summary Using a Perkin-Elmer fluorometer the fluorescence excitation spectra of the four main fluorescencebands of plants (blue, green, red and far-red) were determined in the UV-region between 250 to 400 nm. The results provide valuable information on the most suitable wavelength for fluorescence excitation which is different for the blue and green fluorescence from that of the red and far-red chlorophyll fluorescence. The differing fluorescence yield in dependence of the excitation wavelength can be quantified by the fluorescence ratio blue/red (F450/F690) and blue/far-red (F450/F735), as well as red/far-red (F690/ F735) and blue/green (F450/F530). The differential values of the fluorescence ratios, as found for the usually applied laser-excitation wavelengths of 308, 337, 355 and 397nm, are contrasted. The study demonstrates that fluorescence emission spectra of leaves can successfully be applied for stress detection in plants. The fluorescence ratios blue/red (F450/F690) and blue/far-red (F450/F735) proved to be the most sensitive and best suited stress indicators. For simultaneous excitation of the blue-green fluorescence and the red+far-red chlorophyll fluorescence an excitation wavelength between 355 and 390 nm is recommended. Via fluorescence excitation spectra it was also proved that sun leaves, outdoor plants and highlight treated plants are better protected against UV-A and UV-B than shade leaves, greenhouse plants or low-light plants. The transformation in epidermis cells of UV-radiation into blue and green fluorescence, which can be used by mesophyll cells for photosynthetic quantum conversion, is a new protection mechanism of plants and their photosynthetic apparatus against UV-radiation.