LEAF HAIRS OF OLEA-EUROPAEA PROTECT UNDERLYING TISSUES AGAINST ULTRAVIOLET-B RADIATION-DAMAGE

The photochemical efficiency of photosystem II, as measured by chlorophyll fluorescence induction, was not affected in de-haired olive leaves kept in the dark or intact leaves irradiated with a moderate (3.75 W m-2) ultraviolet-B (UV-B) intensity. In de-haired, UV-B-irradiated leaves, however, the ratio of variable to maximum (F(v)/F(m)) chlorophyll fluorescence declined significantly and irreversibly. Reduction in F(v)/V(m) was associated with an increase in instantaneous and a decrease in maximum (F(m)) fluorescence, indicating perturbation by the UV-B exposure of more than one photosynthetic site. Extensive epidermal browning in de-haired, UV-B irradiated leaves was also observed, indicating possible damage to cell membranes. The results strengthen the hypothesis that leaf hairs protect the underlying tissues against UV-B radiation damage.