Thèse de doctorat en Sciences de l'Univers et Environnement
Sous la direction de Anne Repellin.
Soutenue le 12-09-2013
à Paris Est , dans le cadre de École doctorale Sciences, Ingénierie et Environnement (Champs-sur-Marne, Seine-et-Marne ; 2010-2015) , en partenariat avec Laboratoire Biogéochimie et écologie des milieux continentaux (laboratoire) .
Le président du jury était Yves Jolivet.
Le jury était composé de Anne Repellin, Bertrand Pourrut, Luis Leitao.
Les rapporteurs étaient Renaud Brouquisse, Graham Noctor.
Pas de résumé en français
Effect of tropospheric ozone on wheat (Triticum eastivum L.) : characterization of vacuolar endoproteolytic activity and level of oxidized proteins
The present study was undertaken to investigate whether vacuolar endoproteolysis and/or protein carbonylation (measured here with a newly developed method) were functionally linked and if either of these processes or both could differentiate between ozone sensitive and tolerant wheat cultivars (cvs). Two winter wheat (Triticum aestivum L.) cvs released in 1986 (Soissons) and 2006 (Premio) were grown in the field and exposed to ambient and semi-controlled chronic ozone concentrations, from pre-anthesis to harvest, using a new linear ozone fumigation device that generates gradients of the pollutant. Grain yield and quality were more affected by the ozone treatments in the older cv Soissons that appeared to be the most sensitive. Because stomatal conductance did not differ significantly between the two cvs, differential ozone sensitivity was rather ascribed to differences in the biochemical and molecular responses between the two cvs. Ozone detrimental effects were mainly characterized by premature induction of leaf senescence, causing the shortening of the assimilation and grain-filling periods. Even though Soissons exhibited higher constitutive levels of carbonyl content in total soluble proteins, the increases in protein carbonylation, in response to the ozone treatments, were equivalent in both cvs. Thus basal levels of protein carbonyl seems a more relevant parameters to distinguish between ozone sensitive and tolerant wheat cvs than actual change in this parameter in response to ozone treatments. However, ozone induced more carbonyl groups on Rubisco large subunit (LSU) and small subunit (SSU) in Soissons and this was associated with a more pronounced decline in LSU and SSU contents and a lower Rubisco activity. Increased protein carbonyl levels and losses in total chlorophyll contents were concurrent, suggesting a link between the extent of oxidative stress and senescence development. Moreover, ozone treatments induced a stimulation of endoproteolytic activities that resulted mostly from increases in cysteine protease activities, for both cvs. Surprisingly, total proteolytic and cysteine protease activities were more enhanced in the tolerant cv, whereas elevated proteolysis is usually associated with high sensitivity to environemental stresses, like drought. Expression analysis for three genes encoding papain-like cysteine proteases showed poor correlation with total cysteine protease activities, which suggested that post-transcriptional regulation mechanisms were prevalent over transcriptional ones. Increased endoproteolytic activities were associated with increased protein carbonylation and with a decline in total soluble protein contents. Oxidized proteins could be more susceptible to proteolysis. Therefore, we suggest that ozone-induced ROS caused protein oxidation on one hand and acted as a signal that triggered senescence processes, such as enhanced proteolysis, on the other hand