Assessment of UV-B Stress by Chlorophyll Fluorescence Analysis

UV-B stress was evaluated by measuring chlorophyll fluorescence induction kinetics with the PAM-fluorometer. Commonly used parameters such as Fo, Fm, Fv, Fp, qQ and qE are compared in sunflower seedlings grown under enhanced artificial or solar UV B radiation. It was shown that Fo increased whereas Fm and Fv decreased under enhanced artificial UV-B. Photochemical phase Fo-I1 decreased at a similar degree as “thermal” phase I1-I2. The half life of fluorescence dark decay after a single turnover flash was shorter under UV-B stress. In the steady state photochemical quenching qQ decreased with UV-B exposure whereas energy dependent quenching qE increased. Similar results were obtained under solar radiation at a Mediterranian latitude.