Are Chlorophyll-Carotenoid Interactions Responsible for Rapidly Reversible Non-Photochemical Fluorescence Quenching?
Photoprotective thermal energy dissipation (as assessed via non-photochemical quenching of singlet-excited chlorophyll a, NPQ) in plants is driven by various mechanisms occurring over different time scales. The rapid and reversible part of NPQ, also called qE (for energy-dependent quenching), was demonstrated to correlate with the twisting of a neoxanthin molecule in the light-harvesting antenna as observed by resonance Raman spectroscopy (Nature 450: 575–578, 2007). Interestingly, the extent of fluorescence quenching correlates with the change in Raman signal in different situations: during NPQ in vivo, during fluorescence quenching upon aggregation of LHCII (the major light-harvesting complex in plants), and in crystals of LHCII. In the same study, it was proposed that the quenching is caused by excitation energy transfer from chlorophyll a to lutein in LHCII after a structural change that correlates with the twisting of the neoxanthin. However, this view has been challenged by others for different reasons. Here we discuss the arguments in favor and against this mechanism. A short overview is given of the spectroscopic data on chlorophyll-carotenoid interactions in plant light-harvesting systems, the changes in interactions upon aggregation or crystallization, and the possible relationship to the mechanism of NPQ.
KeywordsExciton State Excitation Energy Transfer Detergent Concentration Thermal Energy Dissipation Trimeric LHCII
Band 4 complex;
Dimeric core of PS II;
Supercomplex of PS II consisting of a dimeric core surrounded by the outer light-harvesting complexes (LHCs): 4 major (LHCII) and 6 minor ones (two each of CP24, CP26 and CP29);
- Chl 610
- Chl 612
- CP24, CP26, CP29
Minor light-harvesting complexes of photosystem II;
Excitation energy transfer;
Light-harvesting complex II;
Moderately coupled LHCII trimer;
Strongly coupled LHCII trimer;
Non-photochemical quenching of chlorophyll fluorescence;
- PS I
- PS II
Reactive oxygen species;
I would like to thank Dr. Roberta Croce for helpful discussions and for providing the figures. I am also obliged to Drs. B. Demmig-Adams, G. Garab, A.R. Holzwarth, and T. Polivka for helpful comments and suggestions. I would like to acknowledge support from the research programme of BioSolar Cells, cofinanced by the Dutch Ministry of Economic Affairs.
- Naqvi KR, Javorfi T, Melo TB, Garab G (1999) More on the catalysis of internal conversion in chlorophyll a by an adjacent carotenoid in light-harvesting complex (Ch1a/b LHCII) of higher plants: time-resolved triplet-minus-singlet spectra of detergent-perturbed complexes. Spectrochim Acta Part A 55:193–204CrossRefGoogle Scholar
- Owens T (1994) Excitation energy transfer between chlorophylls and carotenoids. A proposed molecular mechanism for non-photochemical quenching. In: Baker RRB, Bowyer JR (eds) Photoinhibition in Photosynthesis: From Molecular Mehanisms to the Field. Bios Scientific Publishers, London, pp 95–107Google Scholar
- Van Oort B, Marechal A, Ruban AV, Robert B, Pascal AA, de Ruijter NCA, van Grondelle R, van Amerongen H (2011) Different crystal morphologies lead to slightly different conformations of light-harvesting complex II as monitored by variations of the intrinsic fluorescence lifetime. Phys Chem Chem Phys 13:12614–12622PubMedCrossRefGoogle Scholar