Detection of photosynthetic energy storage in a photosystem I reaction center preparation by photoacoustic spectroscopy

Thomas G. Owens, Robert Carpentier, Roger M. Leblanc

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Abstract

Thermal emission and photochemical energy storage were examined in photosystem I reaction center/core antenna complexes (about 40 Chl a/P700) using photoacoustic spectroscopy. Satisfactory signals could only be obtained from samples bound to hydroxyapatite and all samples had a low signal-to-noise ratio compared to either PS I or PS II in thylakoid membranes. The energy storage signal was saturated at low intensity (half saturation at 1.5 W m-2) and predicted a photochemical quantum yield of >90%. Exogenous donors and acceptors had no effect on the signal amplitudes indicating that energy storage is the result of charge separation between endogenous components. Fe(CN)6-3 oxidation of P700 and dithionite-induced reduction of acceptors FA-FB inhibited energy storage. These data are compatible with the hypothesis that energy storage in PS I arises from charge separation between P700 and Fe-S centers FA-FB that is stable on the time scale of the photoacoustic modulation. High intensity background light (160 W m-2) caused an irreversible loss of energy storage and correlated with a decrease in oxidizable P700; both are probably the result of high light-induced photoinhibition. By analogy to the low fluorescence yield of PS I, the low signal-to-noise ratio in these preparations is attributed to the short lifetime of Chl singlet excited states in PS I-40 and its indirect effect on the yield of thermal emission.

Original languageEnglish (US)
Pages (from-to)201-208
Number of pages8
JournalPhotosynthesis Research
Volume24
Issue number3
DOIs
StatePublished - Jun 1 1990
Externally publishedYes

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Keywords

  • energy conversion
  • P700
  • photosynthesis
  • quantum yield
  • thermal emission

ASJC Scopus subject areas

  • Plant Science

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