Photoinhibition and Law of Reciprocity in Photosynthetic Reactions of Synechocystis sp. PCC 6803

László Nagy, Elisabeth Bálint, James Barber, András Ringler, Katie M. Cook, Peter Maroti

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The effect of irradiance (neutron, alpha, X- and visible electromagnetic rays) on biological systems (survivals of organs, tissue cultures, breakage of DNA) has been widely studied in radiology. The biological effect of radiation depends on the dose (D = I · t; I and t are the intensity and time of irradiance, respectively). In photosynthesis light is a substrate for the photoelectronic conversion and can be toxic to photosystem II (PSII) as well. This toxicity is expressed by the degradation of the reaction centre D 1 protein and, as a consequence, the loss of PSII activity of wild type and mutant Synechocystis cells being subjected to high light. The aim of the present study was to examine whether the photoinhibition of PSII follows the reciprocity law characteristic of a dose response. We measured the change of steady state level of room temperature fluorescence at 685 nm (due to the antenna and reaction center chlorophylls), variable chlorophyll fluorescence and oxygen evolution of wild type Synechocystis 6803 cells after exposure to high light intensities (1200-8000 µmol · m-2 · s-1) for different durations (0-20 min). We observed that the log of degree of PSII inactivation as a function of light intensity gave a straight line, indicating the validity of the reciprocity law. Average cross-sectional areas for inactivation were found to be 0.066 m2/mol (steady state oxygen evolution), 0.12 m2/mol (steady state level of F685nm), and 0.25 m2/mol (induction of Fv/Fmax).

Original languageEnglish
Pages (from-to)410-415
Number of pages6
JournalJournal of Plant Physiology
Issue number4
Publication statusPublished - Jan 1 1995



  • 3-(3,4-dichloro-phenyl)-1,1-dimethylurea
  • DCMU
  • PS-II
  • PSII
  • Photoinhibition
  • Synechocystis 6803
  • fluorescence
  • oxygen evolution
  • photosystem II

ASJC Scopus subject areas

  • Physiology
  • Agronomy and Crop Science
  • Plant Science

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