Energy transfer in the chlorophyll f-containing cyanobacterium, Halomicronema hongdechloris, analyzed by time-resolved fluorescence spectroscopies
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We prepared thylakoid membranes from Halomicronema hongdechloris cells grown under white fluorescent light or light from far-red (740 nm) light-emitting diodes, and observed their energy-transfer processes shortly after light excitation. Excitation–relaxation processes were examined by steady-state and time-resolved fluorescence spectroscopies. Two time-resolved fluorescence techniques were used: time-correlated single photon counting and fluorescence up-conversion methods. The thylakoids from the cells grown under white light contained chlorophyll (Chl) a of different energies, but were devoid of Chl f. At room temperature, the excitation energy was equilibrated among the Chl a pools with a time constant of 6.6 ps. Conversely, the thylakoids from the cells grown under far-red light possessed both Chl a and Chl f. Two energy-transfer pathways from Chl a to Chl f were identified with time constants of 1.3 and 5.0 ps, and the excitation energy was equilibrated between the Chl a and Chl f pools at room temperature. We also examined the energy-transfer pathways from phycobilisome to the two photosystems under white-light cultivation.
KeywordsEnergy transfer Fluorescence Light adaptation Chlorophyll f Pigment-protein complex Time-resolved spectroscopy
Time-resolved fluorescence spectrum (spectra)
This work was supported in part by Grants-in-Aid for Scientific Research from the Ministry of Education of Japan (23370013 to SA, 22370017 to SA and TT, and 24370025, 26220801 to TT), a grant from JST PRESTO (TT), and a Grant from the Australian Research Council’s Discovery Projects funding scheme (project number DP12101360 to TT). MC holds an Australian Research Council Future Fellowship (FT120100464), and MC thanks the Australian Research Council for support (DP120100286, CE140100015). SIA was supported by Grants from the Russian Science Foundation (No: 14-14-00039).
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