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Carbon fixation in Pinus halepensis submitted to ozone. Opposite response of ribulose-1,5-bisphosphate carboxylase/oxygenase and phosphoenolpyruvate carboxylase

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Corresponding author: e-mail: fontaine @scbiol.u-nancy.fr

Abstract

The effects of ozone exposure on carbon-fixation-related processes in Pinus halepensis Mill. needles were assessed over 3 months under controlled conditions. Ozone fumigation (200 ppb) did not induce a modification of either net CO2 assimilation or stomatal conductance in 1-year-old needles, whereas ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) activity was shown to be reduced by a half. Moreover, this ozone-induced reduction in Rubisco activity was associated with a decrease in the quantity of Rubisco, as determined by the decrease in the large subunit (LSU). On the other hand, 200-ppb ozone fumigation induced a strong increase in both activity and quantity of another carboxylating enzyme, phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31), generally considered in C3 plants to participate in carbon catabolism processes. Ozone induced a significant decrease in the Rubisco/PEPC activity ratio which promotes the role of PEPC in trees under ozone stress. The role of this carboxylase will be discussed.

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