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

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.

Photosynthetic parameters of birch (Betula pendula Roth) leaves growing in normal and in CO2‐ and O3‐ enriched atmospheres

“…As a result, the apparent specific activity of Rubisco (k cat ) remained on the same level as in the chamber control (clone 80) or even increased (clone 4) under +O 3 . As the quantity of total soluble protein did not decrease, as also noted earlier (Fontaine et al 1999), stress proteins were probably synthesized instead of Rubisco (Pääkkönen et al 1998a). In both clones the increased mesophyll diffusion resistance r md contrib-uted to the reduction of photosynthesis under +O 3 , although less significantly in clone 4.…”

Ozone and water deficit reduced growth of Aleppo pine seedlings

“…1), we found a significant increase in the stomatal conductance of Pinus halepensis before and during the water stress period and a decrease at the end of experiment. In other O 3 studies on Pinus halepensis, the authors have found a decrease in the stomatal conductance, except in the case of Fontaine et al [13], who found the highest values in the one-year old needles (no significant difference). Several hypotheses have been presented to explain such an increase in gw.…”

Response to an ozone gradient of growth and enzymes implicated in tolerance to oxidative stress inAcer saccharum(Marsh.) seedlings

“…The Rubisco activity was generally not [16]. However, in some other species decreased Rubisco activity and quantity is a more constant response to O 3 [12,33,38].…”

“…Catabolic pathways such as dark respiration, glycolysis and the pentose phosphate pathway have been reported to show increased activity under oxidative stress in some tree species [9,10,12,16,45].…”