Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 110, Issue 24, Pages 10016-10021Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1222606110
Keywords
high light stress; light acclimation; photosynthesis; time-resolved fluorescence
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Funding
- Japan Society for the Promotion of Science through a Research Fellowship for Young Scientists [21001384]
- Cabinet Office through the Funding Program for Next Generation World-Leading Researchers (NEXT Program) [GS026]
- New Energy and Industrial Technology Development Organization through a project for the strategic development of next-generation bioenergy utilization technology [P07015]
- Ministry of Education, Culture, Sports, Science and Technology through the Network of Centers of Carbon Dioxide Resource Studies in Plants
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Plants and green algae have a low pH-inducible mechanism in photosystem II (PSII) that dissipates excess light energy, measured as the nonphotochemical quenching of chlorophyll fluorescence (qE). Recently, nonphotochemical quenching 4 (npq4), a mutant strain of the green alga Chlamydomonas reinhardtii that is qE-deficient and lacks the light-harvesting complex stress-related protein 3 (LHCSR3), was reported [Peers G, et al. (2009) Nature 462(7272): 518-521]. Here, applying a newly established procedure, we isolated the PSII super-complex and its associated light-harvesting proteins from both WT C. reinhardtii and the npq4 mutant grown in either low light (LL) or high light (HL). LHCSR3 was present in the PSII supercomplex from the HL-grown WT, but not in the supercomplex from the LL-grown WT or mutant. The purified PSII supercomplex containing LHCSR3 exhibited a normal fluorescence lifetime at a neutral pH (7.5) by single-photon counting analysis, but a significantly shorter lifetime at pH 5.5, which mimics the acidified lumen of the thylakoid membranes in HL-exposed chloroplasts. The switch from light-harvesting mode to energy-dissipating mode observed in the LHCSR3-containing PSII supercomplex was sensitive to dicyclohexylcarbodiimide, a protein-modifying agent specific to protonatable amino acid residues. We conclude that the PSII-LHCII-LHCSR3 supercomplex formed in the HL-grown C. reinhardtii cells is capable of energy dissipation on protonation of LHCSR3.
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