Effects of in vivo CO2-depletion on electron transport and photoinhibition in the green algae, Chlamydobotrys stellata and Chlamydomonas reinhardtii

Sándor Demeter, Tibor Janda, László Kovács, Dierk Mende, Wolfgang Wiessner

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Short-term illumination of the green algae, Chlamydobotrys stellata and Chlamydomonas reinhardtii in CO2-depleted cultivation medium under low photon flux density (50 and 150 μmol m-2 s-1, respectively) resulted in an inhibition of Photosystem II electron transport from water to diaminodurene, but only slightly affected the electron flow from water to 2,6-dichlorobenzoquinone. The intermediary fluorescence level, Fi was raised to the maximum level of fluorescence, Fm. The initial level of fluorescence, Fo was considerably enhanced. The development of the Fo rise was facilitated by low pH, but inhibited in the presence of an acceptor, dichlorobenzoquinone, or by chemical cross-linking of proteins with glutaraldehyde. The uninhibited electron transport and the original Fo level were restored by readdition of CO2 or by dark adaptation of algae. The observations suggest that in green alga cells CO2-depletion in the light results in a reversible inhibition of steady-state electron flow between the primary (QA) and secondary quinone electron acceptor (QB). Following the inhibition of electron transport a long-lived but reversible state of singly-reduced and probably protonated QA is formed which manifests itself as an apparent Fo rise. Prolonged photoinhibitory illumination of the CO2-depleted green alga cells resulted in an irreversible loss of variable fluorescence and electron transport. The photoinactivation developed more slowly in the CO2-depleted than in the CO2-containing cells. It is concluded that in the bicarbonate-depleted redox state, which is accompanied with an enhanced Fo level of fluorescence, the Photosystem II reaction center is less susceptible to photoinhibition than in the bicarbonate-containing state.

Original languageEnglish
Pages (from-to)166-174
Number of pages9
JournalBBA - Bioenergetics
Issue number2
Publication statusPublished - Apr 26 1995



  • (Green alga)
  • Bicarbonate depletion
  • Electron transport
  • Photoinhibition
  • Photosystem II
  • Thermoluminescence

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

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