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Heat- and light-induced reorganizations in the phycobilisome antenna of Synechocystis sp. PCC 6803. Thermo-optic effect

DOI: 10.1016/j.bbabio.2007.03.002 DOI Help

Authors: K Stoitchkova (Institute of Plant Biology, Hungarian Academy of Sciences, Hungary) , O Zsiros (Institute of Plant Biology, Biological Research Center, Hungarian Academy of Sciences, Hungary) , T Javorfi (Institute of Plant Biology, Biological Research Center, Hungarian Academy of Sciences, Hungary) , T Pali (Institute of Biophysics, Biological Research Center, Hungarian Academy of Sciences, Hungary) , A Andreeva (Department of Condensed Matter Physics, Sofia University, Bulgaria) , Z Gombos (Institute of Plant Biology, Biological Research Center, Hungarian Academy of Sciences, Hungary) , G Garab (Diamond Light Source)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Biochimica Et Biophysica Acta (bba) - Bioenergetics , VOL 1767 , PAGES 750 - 756

State: Published (Approved)
Published: June 2007

Abstract: By using absorption and fluorescence spectroscopy, we compared the effects of heat and light treatments on the phycobilisome (PBS) antenna of Synechocystis sp. PCC 6803 cells. Fluorescence emission spectra obtained upon exciting predominantly PBS, recorded at 25 °C and 77 K, revealed characteristic changes upon heat treatment of the cells. A 5-min incubation at 50 °C, which completely inactivated the activity of photosystem II, led to a small but statistically significant decrease in the F680/F655 fluorescence intensity ratio. In contrast, heat treatment at 60 °C resulted in a much larger decrease in the same ratio and was accompanied by a blue-shift of the main PBS emission band at around 655 nm (F655), indicating an energetic decoupling of PBS from chlorophylls and reorganizations in its internal structure. (Upon exciting PBS, F680 originates from photosystem II and from the terminal emitter of PBS.). Very similar changes were obtained upon exposing the cells to high light (600–7500 μmol photons m−2 s−1) for different time periods (10 min to 3 h). In cells with heat-inactivated photosystem II, the variations caused by light treatment could clearly be assigned to a similar energetic decoupling of the PBS from the membrane and internal reorganizations as induced at around 60 °C. These data can be explained within the frameworks of thermo-optic mechanism [Cseh et al. 2000, Biochemistry 39, 15250]: in high light the heat packages originating from dissipation might lead to elementary structural changes in the close vicinity of dissipation in heat-sensitive structural elements, e.g. around the site where PBS is anchored to the membrane. This, in turn, brings about a diminishment in the energy supply from PBS to the photosystems and reorganization in the molecular architecture of PBS.

Journal Keywords: Energetic decoupling of phycobilisome from photosystems; Fluorescence spectroscopy; Structural changes in phycobilisomes; Synechocystis sp. PCC 6803; Thermo-optic effect

Subject Areas: Biology and Bio-materials


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