Modulation of the fluorescence yield in heliobacterial cells by induction of charge recombination in the photosynthetic reaction center

Autor: Kevin Redding, Stefano Santabarbara, Su Lin, Kiera Reifschneider, Fabrice Rappaport, Iosifina Sarrou
Rok vydání: 2013
Předmět:
Zdroj: Photosynthesis research
120 (2014): 221–235. doi:10.1007/s11120-013-9957-4
info:cnr-pdr/source/autori:Redding K.E.; Sarrou I.; Rappaport F.; Santabarbara S.; Lin S.; Reifschneider K.T./titolo:Modulation of the fluorescence yield in heliobacterial cells by induction of charge recombination in the photosynthetic reaction center/doi:10.1007%2Fs11120-013-9957-4/rivista:Photosynthesis research (Print)/anno:2014/pagina_da:221/pagina_a:235/intervallo_pagine:221–235/volume:120
ISSN: 1573-5079
0166-8595
DOI: 10.1007/s11120-013-9957-4
Popis: Heliobacteria contain a very simple photosyn- thetic apparatus, consisting of a homodimeric type I reac- tion center (RC) without a peripheral antenna system and using the unique pigment bacteriochlorophyll (BChl) g. They are thought to use a light-driven cyclic electron transport pathway to pump protons, and thereby phos- phorylate ADP, although some of the details of this cycle are yet to be worked out. We previously reported that the fluorescence emission from the heliobacterial RC in vivo was increased by exposure to actinic light, although this variable fluorescence phenomenon exhibited very different characteristics to that in oxygenic phototrophs (Collins et al. 2010). Here, we describe the underlying mechanism behind the variable fluorescence in heliobacterial cells. We find that the ability to stably photobleach P800, the primary donor of the RC, using brief flashes is inversely correlated to the variable fluorescence. Using pump-probe spectros- copy in the nanosecond timescale, we found that illumi- nation of cells with bright light for a few seconds put them in a state in which a significant fraction of the RCs underwent charge recombination from P800 ? A0 - with a time constant of *20 ns. The fraction of RCs in the rap- idly back-reacting state correlated very well with the var- iable fluorescence, indicating that nearly all of the increase in fluorescence could be explained by charge recombina- tion of P800 ? A0 - , some of which regenerated the singlet excited state. This hypothesis was tested directly by time- resolved fluorescence studies in the ps and ns timescales. The major decay component in whole cells had a 20-ps decay time, representing trapping by the RC. Treatment of cells with dithionite resulted in the appearance of a *18-ns decay component, which accounted for *0.6 % of the decay, but was almost undetectable in the untreated cells. We conclude that strong illumination of heliobacterial cells can result in saturation of the electron acceptor pool, leading to reduction of the acceptor side of the RC and the creation of a back-reacting RC state that gives rise to delayed fluorescence.
Databáze: OpenAIRE
Externí odkaz: