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-gr een 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 evidenc e that the blue-green fluorescence emission comes mainly from outer ep idermal layers of the leaves and can be transferred on a quartz lamina by quickly dipping the leaves in organic solvents with subsequent sol vent evaporation. Blue-green fluorescence displays a diffusion-control led quenching of fluorescence intensity between 4 degrees C (high fluo rescence) and 37 degrees C (low fluorescence). The blue-green fluoresc ence emissivity is not linked to shortterm metabolic effects other tha n leaf temperature, but epidermis adaptations both to drought and to e xcessive radiation increase emissivity.