REGULATION OF PHOTOCHEMICAL EFFICIENCY OF PHOTOSYSTEM-2 IN NORWAY SPRUCE AT THE BEGINNING OF WINTER AND IN THE FOLLOWING SPRING

Based on the analysis of fluorescence quenching, the nonphotochemical dissipative processes were investigated in Norway spruce needles durin g acclimation to winter and spring conditions. The maximum nonphotoche mical fluorescence quenching (q(Nmax)) was reached at lower irradiance s in winter (up to 310 mu mol m(-2) s(-1)) than in spring (about 1130 mu mol m(-2) s(-1)), but its values were nearly the same (q(Nmax) = 0. 91+/-0.01) during both winter and spring measurements. In early winter the pronounced initial fluorescence quenching (q(0)) suggested that n onradiative energy dissipation in the antennae complexes dominated. Si gnificantly lower q(0) (by 40-60 % compared to winter needles) during acclimation of needles to spring conditions supported a significant co ntribution of quenching in the reaction centres, These findings suppor t the hypothesis that the antennae systems and reaction centres cooper ate in the protective dissipation of excess excitation energy.