Project: Chlorophyll fluorescence, electron transfer and triplet formation during photosynthesis of leaves
Basic processes determining the efficiency of plant photosynthesis are investigated using kinetic methods in intact leaves. Excitation travelling in the antenna is competitively quenched by photochemistry (kP), dissipative thermal (kd), triplet conversion (kT), and fluorescence (kF).
The ratios of these conversions are under investigation. Specifically, triplet accumulation is investigated by fluorescence quenching during strong Xe flashes. The quantum yield of triplet formation and triplet decay - intrinsically, facilitated by transfer to oxygen, and by triplet-singlet annihilation - will be revealed. Along with flash intensity, the singlet density will be varied by inducing non-photochemical quenching, NPQ. Additional quenching of triplets by their interaction with carotenoids during NPQ will be investigated – specifically, can the triplets pass to oxygen in the presence of NPQ?
Fluorescence induction will be investigated in the Xe flashes. The first question is the maximum Ff level obtained after QA reduction: how much is it lower than the Fm level obtained during the full reduction of QA and QB in long saturation pulses? Using experiences obtained, triplet formation will be investigated during the flash fluorescence Ff, compared with Fm. Our hypothesis is that flash fluorescence is still not much quenched by oxidized PSII donor side carriers (Laisk, 2018), but is quenched by the possibility of electron transfer from QA to QB. These studies may open new vistas for understanding chlorophyll fluorescence as determined by electron distribution on PSII acceptor side, and production of singlet oxygen during photosynthesis.
736 6021, 526 7922 (3250)
agu.laisk [ät] ut.ee
Laisk A, Eichelmann H, Oja V (2015) Oxidation of plastohydroquinone by photosystem II and by dioxygen in leaves. Biochim Biophys Acta 1847:565-575
Laisk A, Oja V (2017) Kinetics of photosystem II electron transport: a mathematical analysis based on chlorophyll fluorescence induction. Photosynth Res DOI 10.1007/s11120-017-0439-y
Laisk A, Oja V, Eichelmann H (2016) Kinetics of plastoquinol oxidation by the Q-cycle in leaves. Biochim Biophys Acta 1857:819-830
Laisk A, Oja V, Eichelmann H, Dall’Osto L (2014) Action spectra of photosystems II and I and quantum yield of photosynthesis in leaves in State 1. Biochim Biophys Acta 1837:315-325
Peterson RB, Oja V, Eichelmann H, Bichele I, Dall'Osto L, Laisk A (2014) Fluorescence F0 of photosystems II and I in developing C3 and C4 leaves, and implications on regulation of excitation balance. Photosynth Res 122:41-56