SPECTRAL CHARACTERISTICS AND A POSSIBLE TOPOLOGICAL ASSIGNMENT OF BLUE-GREEN FLUORESCENCE EXCITED BY UV LASER ON LEAVES OF UNRELATED SPECIES

For a number of years it has been known that a relatively strong fluorescence emission is produced by leaves when using UV radiation for excitation (Chappelle et al., 1984a); the apparent bandwidth is larger than 150 nm starting from 400 nm and includes several peaks; under excitation at 337 nm, their integrated energy is 6-11 times the energy released by chlorophyll (a) bands. The problem of bands assignment concerns relative contribution balance as several different emitters are located in chloroplasts, vacuoles, mitochondria, nuclei, cell wall, and epidermis. Within the sensitivity of a 4-lambda synchronous pulse amplified N2 laser photometer, and the experimental limits Of a continuous spectrofluorimeter, the conclusion we present here is that: a) The blue-green fluorescence emission comes mainly from other epidermal layers; b) it is transferable on a quartz lamina by quick dipping the leaves in organic solvents and subsequent solvent evaporation; c) it shows a typical diffusion controlled quenching of fluorescence intensity within a thermal window between 277 K (high fluorescence) and 310 K (low fluorescence); d) the fluorescence emissivity is not linked to short-term metabolic arrangements, but tends to follow long-term epidermis adaptations to drought, and excessive radiation.