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Impact de l'ozone sur les processus photosynthétiques et photorespiratoires du peuplier (Populus x canescens [Aiton] Sm.) au cours du développement foliaire : Aspects écophysiologiques et cellulaires

Abstract : Ozone is considered the most important phytotoxic air pollutant and has well known effects on the metabolism of forest trees. However, the role of leaf development in ozone sensitivity remains unclear. In addition, the photorespiratory pathway has been scarcely investigated under ozone stress. To provide new insights into these issues, young poplar trees (Populus x canescens [Aiton] Sm.) were subjected to 120 ppb of ozone for 35 days in phytotronic chambers. Treated trees displayed foliar symptoms of injury (necrotic spots, chlorosis and precocious leaf senescence) and a reduced stem radial growth. In mature leaves, ozone reduced photosynthesis (A, [phi]PSII) by impairing CO2 fixation, mainly at the level of rubisco (Vcmax and in vitro activity). Photochemistry was also affected as shown by reduced chlorophyll content and Fv/Fm ratio. The rate of in vivo photorespiration and glycolate oxidase activity were reduced along with photosynthetic parameters, suggesting that photosynthesis and photorespiration were both inhibited by the ozone-induced impairment of rubisco. The amount of the H subunit of the glycine decarboxylase and total glutamine synthetase activity were respectively maintained and stimulated. As both enzymes are related to photorespiration, a potential shift in their metabolic involvement could have occurred under ozone stress. In addition, treated leaves showed a stimulation of mitochondrial respiration and phosphoenolpyruvate carboxylase activity which could be related to a higher demand for reducing power to sustain detoxification processes. As none of the parameters were modified by ozone in expanding leaves, ozone sensitivity may appear during leaf development, possibly when developing leaves undergo sink/source transition.
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https://hal.univ-lorraine.fr/tel-01748327
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Matthieu Bagard. Impact de l'ozone sur les processus photosynthétiques et photorespiratoires du peuplier (Populus x canescens [Aiton] Sm.) au cours du développement foliaire : Aspects écophysiologiques et cellulaires. Sylviculture, foresterie. Université Henri Poincaré - Nancy 1, 2008. Français. ⟨NNT : 2008NAN10017⟩. ⟨tel-01748327⟩

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