Tolbert 1995 Proc Natl Acad Sci U S A

Tolbert NE, Benker C, Beck E (1995) The oxygen and carbon dioxide compensation points of C3 plants: Possible role in regulating atmospheric oxygen. Proc Natl Acad Sci U S A 92:11230-33.

» PMID:11607591

Tolbert NE, Benker C, Beck E (1995) Proc Natl Acad Sci U S A

Abstract: The O₂ and CO₂ compensation points (O₂ and CO₂) of plants in a closed system depend on the ratio of CO₂ and O₂ concentrations in air and in the chloroplast and the specificities of ribulose bisphosphate carboxylase/oxygenase (Rubisco). The photosynthetic O₂ is defined as the atmospheric O₂ level, with a given CO₂ level and temperature, at which net O₂ exchange is zero. In experiments with C3 plants, the O₂ with 220 ppm CO₂ is 23 % O₂; O₂ increases to 27 % with 350 ppm CO₂ and to 35 % O₂ with 700 ppm CO₂. At O₂ levels below the O₂, CO₂ uptake and reduction are accompanied by net O₂ evolution. At O₂ levels above the O₂, net O₂ uptake occurs with a reduced rate of CO₂ fixation, more carbohydrates are oxidized by photorespiration to products of the C2 oxidative photosynthetic carbon cycle, and plants senesce prematurely. The CO₂ increases from 50 ppm CO₂ with 21 % O₂ to 220 ppm with 100 % O₂. At a low CO₂/high O₂ ratio that inhibits the carboxylase activity of Rubisco, much malate accumulates, which suggests that the oxygen-insensitive phosphoenolpyruvate carboxylase becomes a significant component of the lower CO₂ fixation rate. Because of low global levels of CO₂ and a Rubisco specificity that favors the carboxylase activity, relatively rapid changes in the atmospheric CO₂ level should control the permissive O₂ that could lead to slow changes in the immense O₂ pool.

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Algae, Photosynthesis