Acclimation of Two Tomato Species to High Atmospheric CO(2): II. Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase and Phosphoenolpyruvate Carboxylase.

Lycopersicon esculentum Mill. cv Vedettos and Lycopersicon chmielewskii Rick, LA 1028, were exposed to two CO(2) concentrations (330 or 900 microliters per liter) for 10 weeks. The elevated CO(2) concentrations increased the initial ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity of both species for the first 5 weeks of treatment but the difference did not persist during the last 5 weeks. The activity of Mg(2+)-CO(2)-activated Rubisco was higher in 900 microliters per liter for the first 2 weeks but declined sharply thereafter. After 10 weeks, leaves grown at 330 microliters per liter CO(2) had about twice the Rubisco activity compared with those grown at 900 microliters per liter CO(2). The two species showed the same trend to Rubisco declines under high CO(2) concentrations. The percent activation of Rubisco was always higher under high CO(2). The phosphoenolpyruvate carboxylase (PEPCase) activity measured in tomato leaves averaged 7.9% of the total Rubisco. PEPCase showed a similar trend with time as the initial Rubisco but with no significant difference between nonenriched and CO(2)-enriched plants. Long-term exposure of tomato plants to high CO(2) was previously shown to induce a decline of photosynthetic efficiency. Based on the current study and on previous results, we propose that the decline of activated Rubisco is the main cause of the acclimation of tomato plants to high CO(2) concentrations.