Non-photochemical fluorescence quenching in photosystem II antenna complexes by the reaction center cation radical

• Published in: Biochemistry (Moscow) Vol. 81; no. 6; pp. 583 - 590
• Main Authors: Paschenko, V. Z., Gorokhov, V. V., Grishanova, N. P., Korvatovskii, B. N., Ivanov, M. V., Maksimov, E. G., Mamedov, M. D.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01.06.2016; Springer; Springer Nature B.V
• Subjects: Arabidopsis - metabolism; Biochemistry; Biomedical and Life Sciences; Biomedicine; Bioorganic Chemistry; Cameras; Cations - chemistry; Chemical reactions; Decay; Dithionite - chemistry; Fluorescence; Fluorometry; Free Radicals - chemistry; Kinetics; Life Sciences; Microbiology; Observations; Photochemicals; Photosystem II Protein Complex - chemistry; Photosystem II Protein Complex - metabolism; Plant Leaves - metabolism; Spectrometry, Fluorescence; photosystem II; non-photochemical quenching; reaction center; photochemical reactions; light-harvesting antenna
• ISSN: 0006-2979; 1608-3040
• DOI: 10.1134/S0006297916060043

In direct experiments, rate constants of photochemical ( k P ) and non-photochemical ( k P + ) fluorescence quenching were determined in membrane fragments of photosystem II (PSII), in oxygen-evolving PSII core particles, as well as in core particles deprived of the oxygen-evolving complex. For this purpose, a new approach to the pulse fluorometry method was implemented. In the “dark” reaction center (RC) state, antenna fluorescence decay kinetics were measured under lowintensity excitation (532 nm, pulse repetition rate 1 Hz), and the emission was registered by a streak camera. To create a “closed” [P680 + Q A – ] RC state, a high-intensity pre-excitation pulse (pump pulse, 532 nm) of the sample was used. The time advance of the pump pulse against the measuring pulse was 8 ns. In this experimental configuration, under the pump pulse, the [P680 + Q A – ] state was formed in RC, whereupon antenna fluorescence kinetics was measured using a weak testing picosecond pulsed excitation light applied to the sample 8 ns after the pump pulse. The data were fitted by a two-exponential approximation. Efficiency of antenna fluorescence quenching by the photoactive RC pigment in its oxidized (P680 + ) state was found to be ∼1.5 times higher than that of the neutral (P680) RC state. To verify the data obtained with a streak camera, control measurements of PSII complex fluorescence decay kinetics by the single-photon counting technique were carried out. The results support the conclusions drawn from the measurements registered with the streak camera. In this case, the fitting of fluorescence kinetics was performed in three-exponential approximation, using the value of τ 1 obtained by analyzing data registered by the streak camera. An additional third component obtained by modeling the data of single photon counting describes the P680 + Pheo – charge recombination. Thus, for the first time the ratio of k P + / k P = 1.5 was determined in a direct experiment. The mechanisms of higher efficiency for non-photochemical antenna fluorescence quenching by RC cation radical in comparison to that of photochemical quenching are discussed.