Biophys J, October 2002, p. 2190-2201, Vol. 83, No. 4

Pigment Organization and Energy Transfer Dynamics in Isolated Photosystem I (PSI) Complexes from Arabidopsis thaliana Depleted of the PSI-G, PSI-K, PSI-L, or PSI-N Subunit

Janne A. Ihalainen,^* Poul Erik Jensen, Anna Haldrup, Ivo H. M. van Stokkum, Rienk van Grondelle, Henrik Vibe Scheller, and Jan P. Dekker

 ^*Department of Chemistry, University of Jyväskylä, FIN-40351 Jyväskylä, Finland;  The Royal Veterinary and Agricultural University, DK-1871 Copenhagen, Denmark; and  Faculty of Sciences, Division of Physics and Astronomy, Vrije Universiteit, 1081 HV Amsterdam, The Netherlands

Green plant photosystem I (PSI) consists of at least 18 different protein subunits. The roles of some of these protein subunits are not well known, in particular those that do not occur in the well characterized PSI complexes from cyanobacteria. We investigated the spectroscopic properties and excited-state dynamics of isolated PSI-200 particles from wild-type and mutant Arabidopsis thaliana plants devoid of the PSI-G, PSI-K, PSI-L, or PSI-N subunit. Pigment analysis and a comparison of the 5 K absorption spectra of the various particles suggests that the PSI-L and PSI-H subunits together bind approximately five chlorophyll a molecules with absorption maxima near 688 and 667 nm, that the PSI-G subunit binds approximately two red-shifted -carotene molecules, that PSI-200 particles without PSI-K lack a part of the peripheral antenna, and that the PSI-N subunit does not bind pigments. Measurements of fluorescence decay kinetics at room temperature with picosecond time resolution revealed lifetimes of ~0.6, 5, 15, 50, 120, and 5000 ps in all particles. The 5- and 15-ps phases could, at least in part, be attributed to the excitation equilibration between bulk and red chlorophyll forms, though the 15-ps phase also contains a contribution from trapping by charge separation. The 50- and 120-ps phases predominantly reflect trapping by charge separation. We suggest that contributions from the core antenna dominate the 15-ps trapping phase, that those from the peripheral antenna proteins Lhca2 and Lhca3 dominate the 50-ps phase, and that those from Lhca1 and Lhca4 dominate the 120-ps phase. In the PSI-200 particles without PSI-K or PSI-G protein, more excitations are trapped in the 15-ps phase and less in 50- and 120-ps phases, which is in agreement with the notion that these subunits are involved in the interaction between the core and peripheral antenna proteins.

Biophys J, October 2002, p. 2190-2201, Vol. 83, No. 4
© 2002 by the Biophysical Society   0006-3495/02/10/2190/12  $2.00

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