Light-saturated photosynthesis - Limitation by electron transport or carbon fixation?

Assaf Sukenik, John Bennett, Paul Falkowski

Research output: Contribution to journalArticlepeer-review

255 Scopus citations


The minimal turnover time, τ, for in vivo electron transport from water to CO2, was calculated from oxygen flash yields and steady-state light-saturated photosynthetic rates in the marine chlorophyte, Dunaliella tertiolecta, cultured at different growth irradiance levels. As cells adapted to lower growth irradiance levels, τ increased from 3.5 to 14.5 ms, in parallel with increases in the contents of chlorophyll a, Photosystem II, PQ, cytochrome b6f, Photosystem I and thylakoid surface density. Thus, at all growth irradiance levels examined, the relative proportion of these membrane-bound electron-transport components remained constant. However, the cellular pool size of ribulose-1,5-bisphosphate carboxylase/oxygenase, determined by radioimmunoassay, was independent of growth irradiance. Hence the ratio of the enzyme to electron-transport chain components varied between 4.8 and 1.2 as a function of growth irradiance levels. The change in this ratio was related quantitatively to the minimal turnover time of electron transport from water to carbon dioxide. Taking into account thylakoid surface density, cellular contents of electron-transport components and diffusion coefficient of plastoquinol, a diffusion time of 2.3 ms was calculated for transport of PQH2 from Photosystem II to cytochrome b6f. This rate is 1.5- to 13-times faster than τ. The data strongly suggest that under nutrient saturated conditions the absolute rate of light-saturated photosynthesis is limited by carbon fixation rather than electron transport. It is predicted, however, that in cells grown above 3000 μmol quanta per m2 per s, electron transport rather than carbon fixation would become the rate-limiting step of light saturated photosynthesis.

Original languageEnglish
Pages (from-to)205-215
Number of pages11
JournalBiochimica et Biophysica Acta - Bioenergetics
Issue number3
StatePublished - 6 May 1987
Externally publishedYes


  • (Dunaliella)
  • Alga
  • Carbon fixation
  • Electron transport
  • Photosystem
  • Reaction center
  • Turnover time

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology


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