TRAP-LIMITED CHARGE SEPARATION KINETICS IN PHOTOSYSTEM I COMPLEXES FROM HIGHER PLANT
Chavdar Slavov 1, Matteo Ballottari 2, Tomas Morosinotto 3, Roberto Bassi 4 and Alfred R. Holzwarth 1*
1 Max-Planck-Inst. fuer Bioanorganische Chemie
2 Dipartimento Scientifico e Tecnologico, Università di Verona
3 Dipartimento di Biologia, Università di Padova
4 Dipartimento Scientifico e Tecnologico, Università di Verona,
* To whom correspondence should be addressed. E-mail: holzwarth{at}mpi-muelheim.mpg.de.
Submitted on July 10, 2007
Revised on August 9, 2007
Accepted on 26 November 2007
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Abstract |
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Time-resolved fluorescence measurements were performed on isolated core and intact Photosystem I particles, and stroma membranes from Arabidopsis thaliana in order to characterize the type of energy trapping kinetics in higher plant Photosystem I. Target analysis confirms the previously proposed "charge recombination" model. No bottleneck in the energy flow from the bulk antenna compartments to the reaction center has been found. For both particles a trap-limited kinetics is realized, with an apparent charge separation lifetime of about 6 ps. No 'red' Chls are found in the PS I-core complex from Arabidopsis thaliana. Rather, the observed red-shifted fluorescence (700-710 nm range) originates from the reaction center. In contrast, two 'red' Chl compartments, located in the peripheral lightharvesting complexes, are resolved in the intact PS I particles (decay lifetimes 33 and 95 ps, respectively). These two 'red' states have been attributed to the two 'red' states found in Lhca 3 and Lhca 4 respectively. The influence of the 'red' Chls on the slowing of the overall trapping kinetics in the intact PS I complex is estimated to be approximately four times larger than the effect of the bulk antenna enlargement.
Key Words:
Photosynthesis, Photosystem I, charge separation, trapping kinetics, ‘red’ chlorophylls
