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

Abstract

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 beta-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.

Regulation of photosystem I light harvesting by zeaxanthin

“…Here, we show that zeaxanthin also down-regulates singlet chlorophyll excited states. The global analysis of the fluorescence decay kinetics of the PSI-LHCI supercomplex found decay components in violaxanthin-binding complexes to be basically in agreement with previous results (5,6,50,51), whereas in presence of zeaxanthin we identified decay components reflecting a reduction of the trapping time of the absorbed excitation energy (Fig. 5).…”

Photoprotection in the Lichen Parmelia sulcata: The Origins of Desiccation-Induced Fluorescence Quenching

“…We resolved an additional short component (t 5 5 40 ps) in this study and assigned it to PSI. Fast decay components with similar lifetimes have been reported in recent studies of various PSI preparations from higher plants (Croce et al, 2000;Ihalainen et al, 2002;Melkozernov et al, 2004) and PSI-rich thylakoid membrane compartments (Veerman et al, 2007). Two distinct PSI decay components are thought to originate from the peripheral and inner PSI antenna (Croce et al, 2000;Melkozernov et al, 2004).…”

Analysis of light-induced transmembrane ion gradients and membrane potential in Photosystem I proteoliposomes

“…It was estimated from the initial lipid to chlorophyll ratio (100:1, w/w), assuming an average of 160 chlorophylls per reaction center for this preparation [32] and an average area of 0.7 nm 2 per lipid molecule [33]. The estimated value was n = 1.5×10 10 cm -2 .…”