BLUE, GREEN AND RED FLUORESCENCE SIGNATURES AND IMAGES OF TOBACCO-LEAVES

Laser-induced fluorescence images of the leaf of an aurea mutant of Ni cotiana tabacum were recorded for the blue and green fluorescence at 4 40 and 520nm and the red chlorophyll fluorescence at 690 and 735nm. Th e results obtained were compared with direct measurements of the fluor escence emission spectra of leaves using a conventional spectrofluorom eter. The highest emission of blue (F440) and green fluorescence (F520 ) within the leaf was found in the leaf veins, particularly the main l eaf vein. In contrast, the intercostal fields of leaves, which exhibit ed the highest chlorophyll content, showed only a very low blue and gr een fluorescence emission, which was much lower than the red and far-r ed chlorophyll fluorescence emission bands (F690 and F735). Correspond ingly, the ratio of blue to red leaf fluorescence F440/F690 of upper a nd lower leaf side was much higher in the leaf veins (values 1.2 to 1. 5) than in intercostal fields (values of 0.6 to 0.7). The results also demonstrated that in the intercostal fields the major part of the blu e-green fluorescence was reabsorbed by chlorophylls and carotenoids. A partial reabsorption of the red fluorescence band near 690 nm by leaf chlorophyll took place, but did not affect the far-red fluorescence b and near F735. As a consequence the chlorophyll fluo-rescence ratio F6 90/F735 exhibited significantly higher values in the chlorophyll-poor leaf vein regions (1.7 to 1.8) than in the chlorophyll-rich intercosta l fields (0.8 to 1.3). Imaging spectroscopy of leaves was shown to be much more precise than the screening of fluorescence signatures by con ventional fluorometers. It clearly demonstrated that the blue-green fl uorescence and the red chlorophyll fluorescence of leaves exhibit an i nverse contrast to each other. The advantage of the fluorescence im ag ing spectroscopy, which allows the simultaneous screening of the whole leaf surface and distinct parts of it, and its possible application i n the detection of stress effects or local damage by insects and patho gens, is discussed.