Changes in the chloroplastic CO2 concentration explain much of the observed Kok effect: a model ($)

When the uptake of CO2 (A) is plotted against absorbed irradiance (I), at low I there is a noticeable bend that occurs around the light compensation point (I where CO2 release due to mitochondrial respiration is balanced by CO2 uptake by photosynthesis). When the slopes of both parts of the curve are extrapolated back to zero irradiance, it appears as though the rate of mitochondrial respiration is greater in the dark than the light; the inference that there is a light-dependent inhibition of respiration is known as the “Kok effect”.  Farquhar and Busch propose a model to explain the Kok effect, in which the apparent curvature of the A vs I plot is attributable to changes in chloroplastic CO2 partial pressure at low I. They suggest that the Kok effect is related to photorespiration, which is consistent with a reduced Kok effect seen in C4 plants, or high CO2 or low O2 conditions. New Phytol. 10.1111/nph.14512

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