PARENT SESSION
Posters P4Ab Type II reaction centres: Acceptor side. Abstracts (272-288)

Intrinsic changes to PSII reaction center properties in mutants of Arabidopsis as probed by thermoluminescence. Luke Hendrickson^*,1, Alexander Ivanov^{1, 2}, Norman Huner², Gunnar Öquist¹, Vaughan Hurry¹, ¹ Umeå Plant Science Center, Umeå, Vasterbotten, Sweden² Biology Department, London, Ontario, Canada

ABSTRACT- The thermoluminescence and chlorophyll fluorescence properties of photosystem II (PSII) reaction centers, together with measurements of P700, were assessed in various lipid and electron transport mutants of Arabidopsis (Arabidopsis thaliana). As expected, results from the comparative analysis of the mutants showed impaired photosynthetic electron transport rates and an increased dependence upon thermal dissipation at light intensities above growth conditions. The exception to this observation was the cytochrome b₆/f mutant, pgr1, which showed a limited flux of energy via thermal dissipation. De-convolution of the thermoluminescence traces for these mutants revealed significant shifts in the peak temperature of both the S₂Q_A^2- and S₂Q_B^2-, representing significant shifts to the intrinsic redox properties of the PSII reaction center. A comparison between these temperature shifts and those brought about by cold-acclimation of wild-type Arabidopsis¹ suggest that modification of the lipid environment and/or increases in the excitation pressure on PSII increases the dependence on PSII reaction center quenching. These results are further discussed with reference to the current model for reaction center quenching as proposed by Sane et al.^{1 1} Sane PV, Ivanov AG, Hurry V, Huner NPA & quist G (2003) Changes in the redox potential of primary and secondary electron-accepting quinones in photosystem II confer increased resistance to photoinhibition in low temperature-acclimated Arabidopsis. Plant Physiology 132: 2144-2151

KEY WORDS: photosystem II, reaction center, Thermoluminescence, Arabidopsis