The negative feedback molecular mechanism which regulates excitation level in the plant photosynthetic complex LHCII: Towards identification of the energy dissipative state

• Published in: Biochimica et biophysica acta 2013-03, Vol.1827 (3), p.355-364
• Main Authors: Zubik, Monika, Luchowski, Rafal, Puzio, Michal, Janik, Ewa, Bednarska, Joanna, Grudzinski, Wojciech, Gruszecki, Wieslaw I.
• Format: Article
• Language: English
• Subjects: Chlorophyll - chemistry; Feedback, Physiological; Fluorescence quenching; LHCII; Light; Light-Harvesting Protein Complexes - chemistry; Photoprotection; Photosynthesis; Photosynthetic Reaction Center Complex Proteins - chemistry; Spectrometry, Fluorescence; Temperature; Xanthophyll
• ISSN: 0005-2728; 0006-3002; 1879-2650
• DOI: 10.1016/j.bbabio.2012.11.013

Overexcitation of the photosynthetic apparatus is potentially dangerous because it can cause oxidative damage. Photoprotection realized via the feedback de-excitation in the pigment–protein light-harvesting complex LHCII, embedded in the chloroplast lipid environment, was studied with use of the steady-state and time-resolved fluorescence spectroscopy techniques. Illumination of LHCII results in the pronounced singlet excitation quenching, demonstrated by decreased quantum yield of the chlorophyll a fluorescence and shortening of the fluorescence lifetimes. Analysis of the 77K chlorophyll a fluorescence emission spectra reveals that the light-driven excitation quenching in LHCII is associated with the intensity increase of the spectral band in the region of 700nm, relative to the principal band at 680nm. The average chlorophyll a fluorescence lifetime at 700nm changes drastically upon temperature decrease: from 1.04ns at 300K to 3.63ns at 77K. The results of the experiments lead us to conclude that: (i) the 700nm band is associated with the inter-trimer interactions which result in the formation of the chlorophyll low-energy states acting as energy traps and non-radiative dissipation centers; (ii) the Arrhenius analysis, supported by the results of the FTIR measurements, suggests that the photo-reaction can be associated with breaking of hydrogen bonds. Possible involvement of photo-isomerization of neoxanthin, reported previously (Biochim. Biophys. Acta 1807 (2011) 1237-1243) in generation of the low-energy traps in LHCII is discussed. [Display omitted] ► Illumination of LHCII induces excitation quenching. ► Excitation quenching is associated with appearance of the emission band at 700nm. ► The 700nm band is attributed to inter-trimer LHCII interactions.