Fluorescence is emitted by diverse living organisms. The analysis and interpretation of these signals may give information about their physiological state, ways of communication among species and the presence of specific chemicals. In this manuscript we review the state of the art in the research on the fluorescence emitted by plant leaves, fruits, flowers, avians, butterflies, beetles, dragonflies, millipedes, cockroaches, bees, spiders, scorpions and sea organisms and discuss its relevance in nature.

Fluorescence, the absorption of short-wavelength electromagnetic radiation reemitted at longer wavelengths, has been suggested to play several biological roles in metazoans. This phenomenon is uncommon in tetrapods, being restricted mostly to parrots and marine turtles. We report fluorescence in amphibians, in the tree frog Hypsiboas punctatus, showing that fluorescence in living frogs is produced by a combination of lymph and glandular emission, with pigmentary cell filtering in the skin. The chemical origin of fluorescence was traced to a class of fluorescent compounds derived from dihydroisoquinolinone, here named hyloins. We show that fluorescence contributes 18−29% of the total emerging light under twilight and nocturnal scenarios, largely enhancing brightness of the individuals and matching the sensitivity of night vision in amphibians. These results introduce an unprecedented source of pigmentation in amphibians and highlight the potential relevance of fluorescence in visual perception in terrestrial environments.

True fluorescence spectra of leaves are obtained combining experimental emission and reflectance data. The model used is validated by measuring the system fluorescence in the absence of reabsorption processes (thin layer of chloroplasts).

Aggregation equilibrium and the fluorescence properties of hydroxoaluminium tricarboxymonoamidephthalocyanine adsorbed on microgranular cellulose have been studied at different dye loadings. Up to a concentration of nearly 3 × 10⁻⁶ mol phthalocyanine (g cellulose)⁻¹ diffuse reflectance spectra may be interpreted on the basis of a simple monomer–dimer equilibrium. Monomer and dimer spectra are similar to the spectra of the monomeric dye in solution. The solid-state dimer spectrum is red-shifted with respect to that of the monomer and this is attributed to the coplanarity of dimers. Fluorescence spectra and quantum yields show typical effects of re-absorption and re-emission of light. In particular, the observed fluorescence quantum yields depend on concentration and span the range 0.29–0.07. To account for these effects as well as the effect of aggregation on fluorescence quantum yields and to obtain corrected fluorescence spectra a model based on the Kubelka–Munk theory of diffuse reflectance is developed. The application of this model to the case under study yields a true fluorescence quantum yield ϕ = 0.46 ± 0.02 in the whole range of concentrations, which is slightly higher than the value found for the same dye in dimethyl sulfoxide solution.

Emission fluorescence spectra were obtained for the adaxial and abaxial faces of dicotyledonous (Ficus benjamina L., Ficus elastica, Gardenia jasminoides and Hedera helix) and monocotyledonous leaves (Gladiolus spp. and Dracaena cincta bicolor). After correction by light-re-absorption processes, using a previously published physical model, the adaxial faces of dicotyledons showed a fluorescence ratio F_red/F_far-red rather lower than the respective values for the abaxial faces. Monocotyledons and shade-adapted-plants showed similar values for the corrected fluorescence ratio for both faces. Even when differences in experimental fluorescence emission from adaxial and abaxial leaves in dicotyledons are mostly due to light re-absorption processes, the residual dissimilarity found after application of the correction model would point to the fact that fluorescence re-absorption is not the only responsible for the observed disparity. It was concluded that light re-absorption processes does not account entirely for the differences in the experimental emission spectra between adaxial and abaxial leaves. Differences that remains still present after correction might be interpreted in terms of a different photosystem ratio (PSII/PSI). Experiments at low temperature sustained this hypothesis. In dicotyledons, light reflectance for adaxial leaves was found to be lower than for the abaxial ones. It was mainly due to an increase in the scattering coefficient for the lower leaf-side. The absorption coefficient values were slightly higher for the upper leaf-side. During senescence of Ficus benjamina leaves, the scattering coefficient increased for both the upper and lower leaf-sides. With senescence time the absorption coefficient spectra broadened while the corrected fluorescence ratio (F_red/F_far-red) decreased for both faces. The results pointed to a preferential destruction of photosystem II relative to photosystem I during senescence.