Evidence for a physiological role of CO2 in the regulation of photosynthetic electron transport in intact leaves

Clive R. Ireland, Neil R. Baker, Stephen P. Long

Research output: Contribution to journalArticlepeer-review


The effect of CO2 upon photosynthetic electron transport was examined in wheat and maize leaves in order to establish whether CO2 had a direct role in electron-transport regulation in vivo. When intercellular CO2 was depleted a transient rise in chlorophyll fluorescence occurred which correlated with an increase in the reduction of the Photosystem II primary quinone acceptor, QA, and a decrease in CO2 fixation rate. However, when intercellular CO2 was reduced from an already low level (50 μmol·mol-1) towards zero a substantial further reduction in QA occurred with little change in fluorescence or CO2 fixation. In very low intercellular CO2 when no measurable CO2 fixation was sustained, an appreciable fraction of QA still remained oxidised, however, maximal reduction of QA occurred when O2 was also removed. QA could then be substantially reoxidised by the readdition of small amounts of CO2 (20-40 μmol) which only facilitated a very small increase in CO2 fixation. Changes in the kinetics of the fast rise in fluorescence emission indicated that QA-to-QB electron transfer was decreased in a CO2-free atmosphere and QB was poised in a more oxidised state. Electron transport that was independent of CO2 fixation was measured in methyl viologen-treated leaf discs. In 1% O2, but not in 21% O2, light-dependent electron transport to methyl viologen was decreased significantly by the depletion of CO2. It is concluded that CO2 can modify the redox state of Photosystem II electron transport acceptors in vivo independently of carbon assimilation and that there is a complex interaction between CO2 and O2 in the regulation of photosynthetic electron transport. The possibility that CO2 operates via the reversible binding to PS II and thereby acts as a cofactor for efficient PS II electron transport in the leaf is discussed.

Original languageEnglish (US)
Pages (from-to)434-443
Number of pages10
JournalBBA - Bioenergetics
Issue number3
StatePublished - Oct 7 1987
Externally publishedYes


  • (T. aestivum L.)
  • (Z. mays L.)
  • Carbon assimilation
  • Carbon dioxide
  • Chlorophyll fluorescence
  • Oxygen
  • Photosynthetic electron transport

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology


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