Caractérisation Biochimique Et Moléculaire.

Résumé: Plant drought tolerance requires the activation of complex metabolic including antioxidative pathways, especially reactive oxygen species (ROS) scavenging enzymatic systems. In this study, 10 durum wheat genotypes (Triticum durum Desf.) were evaluated under drought stress conditions, in order to highlight the correlations between genetic diversity identified through enzymatic markers : superoxide dismutase (SOD), catalase (CAT), peroxidase (POX) and water stress tolerance properties. Firstly, in the first assay, we characterized the impact of oxidative stress and assessed the performance of different cultivars of durum wheat under drought, heat and paraquat stress. The activities of enzymatic antioxidants SOD, CAT, GPOX and oxidative biomarkers were measured : lipid peroxidation, H2O2 content, membrane stability, and total chlorophyll content. In addition, a correlation analysis between antioxidant enzymes, oxidative markers and physiological parameters related to water status was performed. Results indicated that the 3 treatments decreased membrane stability, chlorophyll content and increased lipid peroxidation, H2O2 content and activities of antioxidant enzymes. However, there were significant differences between wheat cultivars in amounts of decrease or increase in the measured traits. Correlation analysis between biochemical and physiological parameters revealed the singularity of SOD enzyme, which is particularly related to the relative water content, stomatal conductance and total chlorophyll content, The second part of this thesis was devoted to the study of the genetic variability of the three foliar enzymatic systems which allowed us to refine the results of the biochemical and physiological analysis as well as to highlight the influence of water stress on the metabolism of these enzymes in wheat plants grown hydroponically and treated with PEG 6000. An approach based on native PAGE has been developed to evaluate whether the observed overall variations, resulted from qualitative (presence/absence) or quantitative variations specific to certain isoenzymes. Marked differences were detected in the profiles of the studied 3 enzymatic systems studied. Electrophoretic analysis showed the induction of new isoforms and an increase in their intensity in durum wheat cultivars under water stress. Finally, the study of the expression of genes coding for these enzymes, in leaf cells of durum wheat was conducted through RealTime quantitative RT-PCR. Expression levels of 3 genes coding for CAT (TdCAT1, CATA, CAT3), 3 genes coding for POX (Pox3, TaPrx107, TaPrx115) and 2 genes coding for SOD (TdMnSOD, SOD1.1) were differently affected by drought. A variation in transcript accumulation was observed in response to water stress. This molecular approach identified the genes CATA, CAT3, TdMnSOD and SOD1.1 as candidate genes for potential genetic engineering targets and research for molecular markers as a selection tool for improving the tolerance of durum wheat to water stress.

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