| 研究実績の概要 |
In green algae and mosses, LHCSR3 (light-harvesting complex stress related 3) is responsible for a pH-dependent dissipation of absorbed light energy, which is vital to survive against strong light conditions. Recently, purifying the photosystem II (PSII) supercomplex from green algae Chlamydomonas reinhardtii revealed that LHCSR3 binds to the PSII supercomplex and transform it into an energy-dissipative form at acidic pH conditions. However, the detail mechanism how LHCSR3 transforming the PSII supercomplex into an energy-dissipative form remains unclear. Here we show that LHCSR3 modulates the excitation energy flow and dissipates the excitation energy within the light-harvesting complexes (LHCs) of the PSII supercomplex in C. reinhardtii. We found in fluorescence decay associated spectra analysis that when the PSII supercomplex is associated with LHCSR3 excitation energy transfer from LHCs to CP43 is inhibited, consistent with the reduced fluorescence emission from CP43 in high-light acclimated cells. We further characterized the pH-dependent and LHCSR3-dependent quenching of the PSII-LHCII-LHCSR3 supercomplex as accompanying by a fluorescence emission centered at 684 nm with the rate constant of 16 ps-1, which corresponds to the previously reported charge transfer quenching model in the reconstituted LHCSR3. Our results provide a mechanism how LHCSR3 transform the PSII supercomplex as well as an insight into the molecular details of the LHCSR3-dependent quenching.
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