Background
At their natural environment plants are exposed to high fluxes of photosynthetically active and UV radiation. The increased synthesis of UV-absorbing compounds, such as flavonoids and other polyphenols, are accepted as a plant response to increased UV radiation. The increase of leaf flavonoid content can be a protection against the harmful effect of UV-B radiation as they function as antioxidant and UV filters in plants. Differences between sun and shade leaves (adapted to high light and low light respectively) of some tree species are analysed, taking in consideration differences on the UV-A absorption via fluorescence imaging of leaves.