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Photosystem I particles (PSI-200) isolated from spinach leaves were studied by means of absorbance, 77K fluorescence, and resonance Raman spectroscopy. The aim was to obtain better insight into the changes of in the pigment spectral properties of pigments molecules in those Photosystem I particles during prolonged exposure to high-light intensities and to reveal the involvement of these pigments in the photoprotection of the Photosystem I. particles. During prolonged exposure to high-light intensities of spinach Photosystem I particles, a loss of a significant amount of photosynthetic pigments was observed. It was shown that various pigments exhibited different susceptibility to photodamage. effect. In addition to bleaching of chlorophyll a, bleaching of carotenoids was also clearly observed. Resonance Raman technique allowed us to recognize the type and conformation of photobleached carotenoid molecules. Raman data revealed a nearly full photobleaching of the long-wavelength lutein molecules. The observed similar bleaching rate of the lutein molecules and the most red-shifted long-wavelength chlorophyll a absorbing pigments, located in the antenna membrane protein Lcha4, suggested that these molecules are located closely. Our results showed that the photobleached antenna pigments and especially luteins and the long-wavelength absorbing chlorophylls, being dimers or pigment aggregates, are involved in photoprotection of PSI core complex.
This work was supported by the Program “Support for the research activities at the universities” (project № 11/2005) and by the Foundation for the Scientific Research at Sofia University, Bulgaria (project № 74/2006).
Peer reviewed