BLUE-GREEN FLUORESCENCE EXCITED BY UV LASER ON LEAVES OF DIFFERENT SPECIES ORIGINATES FROM CUTIN AND IS SENSITIVE TO LEAF TEMPERATURE

Under ultra-violet excitation, intact leaves generate a strong blue-green fluorescence emission with several bands. Their integrated energy is 6 to 11 times the energy released by chlorophyll a bands (Chappelle ct al. 1984, Applied Optics 23, 134-138). This paper provides evidence that the blue-green fluorescence emission comes mainly from outer epidermal layers of the leaves and can be transferred on a quartz lamina by quickly dipping the leaves in organic solvents with subsequent solvent evaporation. Blue-green fluorescence displays a diffusion-controlled quenching of fluorescence intensity between 4 degrees C (high fluorescence) and 37 degrees C (low fluorescence). The blue-green fluorescence emissivity is not linked to shortterm metabolic effects other than leaf temperature, but epidermis adaptations both to drought and to excessive radiation increase emissivity.