Changes in the chloroplastic CO2concentration explain much of the observed Kok effect: a model.
Mitochondrial respiration often appears to be inhibited in the light when compared with measurements in the dark. This inhibition is inferred from the response of the net CO2assimilation rate (A) to absorbed irradiance (I), changing slope around the light compensation point (Ic). We suggest a model that provides a plausible mechanistic explanation of this 'Kok effect'. The model uses the mathematical description of photosynthesis developed by Farquhar, von Caemmerer and Berry; it involves no inhibition of respiration rate in the light. We also describe a fitting technique for quantifying the Kok effect at low I. Changes in the chloroplastic CO2partial pressure (Cc) can explain curvature of A vs I, its diminution in C4plants and at low oxygen concentrations or high carbon dioxide concentrations in C3plants, and effects of dark respiration rate and of temperature. It also explains the apparent inhibition of respiration in the light as inferred by the Laisk approach. While there are probably other sources of curvature in A vs I, variation in Cccan largely explain the curvature at low irradiance, and suggests that interpretation of day respiration compared with dark respiration of leaves on the basis of the Kok effect needs reassessment.
Research School of Biology, Australian National University, Acton, ACT, 2601, Australia.
Graham D
GD
Farquhar
Research School of Biology, Australian National University, Acton, ACT, 2601, Australia.
Florian A
FA
Busch
D002245:Carbon Dioxide / Q000378:metabolism*; D002736:Chloroplasts / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D008027:Light; D008954:Models, Biological; D010100:Oxygen / Q000494:pharmacology; D010313:Partial Pressure; D055668:Photochemical Processes; D010788:Photosynthesis / Q000187:drug effects / Q000528:radiation effects; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D013696:Temperature
D002245:Carbon Dioxide; D010100:Oxygen
Kok effect; Laisk method; biochemical photosynthesis model; chloroplastic CO2 concentration; day respiration; fitting tool; irradiance; mitochondrial respiration