Time-resolved fluorescence of photosystem I in vivo: Global and target analysis

Abstract

Photosystem I (PSI) is a multi-pigment-protein complex that co-operates with photosystem II (PSII) and uses light energy to transfer electrons from plastocyanin or cytochrome to ferredoxin and eventually to NADP+. Cyanobacterial BE mutant cells that lack PSII and light-harvesting phycobilisomes, provided us with the possibility to study the picosecond fluorescence kinetics of PSI in vivo and the results were analyzed using global and target analysis. The obtained components (5.4 ± 0.14 ps spectral equilibration and 27.8 ± 0.09 ps excitation trapping) are very similar to those found before for isolated PSI. The rate of energy transfer from red-shifted chlorophyll a (Chl a) molecules to bulk Chls a occurs with a rate constant of (7.4–10.4 ps)−1 whereas the reverse process occurs with a rate constant of (19.3–29.8 ps)−1 according to the target analysis, whereas trapping from bulk Chls a occurs with rate (16.8–25.0 ps)−1.