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 fluor escence emission is produced by leaves when using UV radiation for exc itation (Chappelle et al., 1984a); the apparent bandwidth is larger th an 150 nm starting from 400 nm and includes several peaks; under excit ation at 337 nm, their integrated energy is 6-11 times the energy rele ased by chlorophyll (a) bands. The problem of bands assignment concern s relative contribution balance as several different emitters are loca ted in chloroplasts, vacuoles, mitochondria, nuclei, cell wall, and ep idermis. Within the sensitivity of a 4-lambda synchronous pulse amplif ied N2 laser photometer, and the experimental limits Of a continuous s pectrofluorimeter, 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 withi n a thermal window between 277 K (high fluorescence) and 310 K (low fl uorescence); d) the fluorescence emissivity is not linked to short-ter m metabolic arrangements, but tends to follow long-term epidermis adap tations to drought, and excessive radiation.