PARENT SESSION
Posters P3B Photosynthetic acclimation: Ecophysiology, diverse environments. Abstracts (479-522)

Effect of a realistic ozone stress on the carboxylases (PEPC and Rubisco) of bean. Jean-Philippe BIOLLEY^*,1, Louis LEITAO¹, Pierre DIZENGREMEL², ¹ Laboratoire d'Ecologie Moléculaire, EA 3525, IBEAS, PAU, FRANCE² Ecologie et Ecophysiologie Forestières, Vandoeuvre, FRANCE

ABSTRACT- Using open-top chamber technology we aimed to investigate the impact of a chronic and realistic ozone stress on the carboxylating enzymes of bean (Phaseolus vulgaris L.). In C₃ species, Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) is involved in photosynthetic carbon fixation whereas PEPC (phosphoenolpyruvate carboxylase) is known to replenish Krebs cycle intermediates in order to allow synthesis of organic acids and amino acids. Bean plants were exposed 20 days after emergence to three different atmospheres characterized by seasonal 7-h mean ozone concentrations of 47 (control), 86 and 122 ppb. At the harvest date, photosynthetic pigment content was significantly depressed only in mature primary leaves from 122 ppb ozone treatment. On the contrary, pigmentation of young first trifoliate leaves that were not fully expanded tended to be slightly increased in the two ozone-enriched treatments. Carboxylase activities measured in control conditions depended on leaf type. As compared with primary leaves, total Rubisco activity of first trifoliate leaf was 31% lower and PEPC activity increased by 3.7-fold. In any case, ozone-induced changes in enzyme activities were only observed in 122 ppb treatment. In primary leaves, an AOT40 ozone dose of 10763 ppb.h reduced the total Rubisco activity by about 33% whereas it increased the PEPC activity by about 376%, relative to the control. Such an opposite response between Rubisco and PEPC was not detected in young first trifoliate leaf that has suffered a reduced AOT40 ozone dose (7995 ppb.h) since it has emerged after primary leaves. On the contrary, this ozone dose increased the total Rubisco activity in first trifoliate leaf by about 33% whereas it had no impact on PEPC activity. To conclude, it appeared that the response of the two carboxylases to ozone may vary according to both stress intensity and physiological age of the leaf.

KEY WORDS: ozone, bean, pepc, rubisco