Effect of chronic O3 fumigation on the activity of some Calvin cycle enzymes in two poplar clones

The effects of long-term exposure to ozone (O-3, 60 mm(3) m(-3) for 5 h d(-1)) on some Calvin cycle enzymes, in particular those modulated by the thioredoxin system, were studied in two poplar clones. These clones differ in sensitivity to O-3. In the 1-214 clone, the first effects from O-3 treatment were seen after 40 d of fumigation, while the Eridano clone showed visible symptoms of damage after only 15 d of the treatment. Specific activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (E.C. 4.1.1.39) diminished in both the clones, while specific activity of phosphoenolpyruvate carboxylase (E.C. 4.1.1.31) increased. Exposure to O-3 also caused a reduction in the specific activity of ribulose-1,5-bisphosphate kinase (E.C. 2.7.1.19) in both clones. At the end of the exposure to 03, specific activity of glyceraldehyde 3-phosphate dehydrogenase (E.C. 1.2.1.13) increased in 1-214 and remained similar to the control in Eridano, whereas specific activity of fructose-1,6-bisphosphate phosphatase (E.C. 3.1.3.11) was higher in Eridano and similar to the control in 1-214.