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 during acclimation to winter and spring conditions. The maximum nonphotochemical fluorescence quenching (q(Nmax)) was reached at lower irradiances 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 nonradiative energy dissipation in the antennae complexes dominated. Significantly lower q(0) (by 40-60 % compared to winter needles) during acclimation of needles to spring conditions supported a significant contribution of quenching in the reaction centres, These findings support the hypothesis that the antennae systems and reaction centres cooperate in the protective dissipation of excess excitation energy.