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The mechanism of charge recombination of the S(2)Q(A)(-) state in photosystem II was investigated by modifying the free energy gap between the quinone acceptor Q(A) and the primary pheophytin acceptor Ph. This was done either by changing the midpoint potential of Ph (using mutants of the cyanobacterium Synechocystis with a modified hydrogen bond to this(More)
In photosynthetic chains, the kinetics of fluorescence yield depends on the photochemical rates at the level of both Photosystem I and II and thus on the absorption cross section of the photosynthetic units as well as on the coupling between light harvesting complexes and photosynthetic traps. A new set-up is described which, at variance with the commonly(More)
The energetic metabolism of photosynthetic organisms is profoundly influenced by state transitions and cyclic electron flow around photosystem I. The former involve a reversible redistribution of the light-harvesting antenna between photosystem I and photosystem II and optimize light energy utilization in photosynthesis whereas the latter process modulates(More)
Photosynthesis is the biological process that feeds the biosphere with reduced carbon. The assimilation of CO2 requires the fine tuning of two co-existing functional modes: linear electron flow, which provides NADPH and ATP, and cyclic electron flow, which only sustains ATP synthesis. Although the importance of this fine tuning is appreciated, its mechanism(More)
Recent progress in two-dimensional and three-dimensional electron and X-ray crystallography of Photosystem II (PSII) core complexes has led to major advances in the structural definition of this integral membrane protein complex. Despite the overall structural and kinetic similarity of the PSII reaction centers to their purple non-sulfur photosynthetic(More)
We investigated the dependence of both the quantum yield of charge separation and pathways of charge recombination on the free energy level of the radical pair state P 1 Ph À in photosystem II. This was done by comparing the basal (F 0) fluorescence yield and the recombination rate of the S 2 Q A À state in various strains of Chlamydomonas reindhardtii in(More)
Two homologous plastocyanin isoforms are encoded by the genes PETE1 and PETE2 in the nuclear genome of Arabidopsis thaliana. The PETE2 transcript is expressed at considerably higher levels and the PETE2 protein is the more abundant isoform. Null mutations in the PETE genes resulted in plants, designated pete1 and pete2, with decreased plastocyanin contents.(More)
When unicellular algal cells are placed under anaerobic conditions, a large electrochemical gradient is built in darkness across the thylakoid membranes. We have estimated, in vivo, the amplitude of the Delta pH component of this transmembrane potential and shown that the Delta pH is twice as large as the Delta Psi. The amplitude of the Delta mu tildeH+(More)
Central in respiration or photosynthesis, the cytochrome bc(1) and b(6)f complexes are regarded as functionally similar quinol oxidoreductases. They both catalyse a redox loop, the Q-cycle, which couples electron and proton transfer. This loop involves a bifurcated electron transfer step considered as being mechanistically mandatory, making the Q-cycle(More)
A major challenge in biology is to identify molecular polymorphisms responsible for variation in complex traits of evolutionary and agricultural interest. Using the advantages of Arabidopsis thaliana as a model species, we sought to identify new genes and genetic mechanisms underlying natural variation for shoot growth using quantitative genetic strategies.(More)