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. 1983 Apr;71(4):955–960. doi: 10.1104/pp.71.4.955

Photosynthesis and Activation of Ribulose Bisphosphate Carboxylase in Wheat Seedlings 1

Regulation by CO2 and O2

John T Perchorowicz 1,2, Richard G Jensen 1,2,2
PMCID: PMC1066150  PMID: 16662935

Abstract

Photosynthetic carbon assimilation in plants is regulated by activity of the ribulose 1,5-bisphosphate (RuBP) carboxylase/oxygenase. Although the carboxylase requires CO2 to activate the enzyme, changes in CO2 between 100 and 1,400 microliters per liter did not cause changes in activation of the leaf carboxylase in light. With these CO2 levels and 21% O2 or 1% or less O2, the levels of ribulose bisphosphate were high and not limiting for CO2 fixation. With high leaf ribulose bisphosphate, the Kact(CO2) of the carboxylase must be lower than in dark, where RuBP is quite low in leaves. When leaves were illuminated in the absence of CO2 and O2, activation of the carboxylase dropped to zero while RuBP levels approached the binding site concentration of the carboxylase, probably by forming the inactive enzyme-RuBP complex.

The mechanism for changing activation of the RuBP carboxylase in the light involves not only Mg2+ and pH changes in the chloroplast stroma, but also the effects of binding RuBP to the enzyme. In light when RuBP is greater than the binding site concentration of the carboxylase, Mg2+ and pH most likely determine the ratio of inactive enzyme-RuBP to active enzyme-CO2-Mg2+-RuBP forms. Higher irradiances favor more optimal Mg2+ and pH, with greater activation of the carboxylase and increased photosynthesis.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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