[en] Investigations carried out during this thesis consisted in the research of volatile and non-volatile abiotic stress markers using winter oilseed rape (Brassica napus L.), a major crop worldwide. Two specific abiotic stresses involved in current agricultural soil threats were studied such as cadmium (Cd), a carcinogen trace heavy metal, and epoxiconazole being a persistent systemic fungicide. A targeted metabolomic approach was therefore used through the analysis of volatile organic compounds (VOCs) profiles, targeting terpenoid compounds largely described in plant abiotic stress response, and through the profiling of glucosinolates (GSLs) as non-volatile sulfur-containing metabolites within Brassicaceae.
A new glass device allowing the plantlets growth and the non-invasive dynamic sampling of emitted VOCs was successfully developed. It can be described as an innovative laboratory and high-throughput plant chambers system. Oilseed rape plantlets analysis was performed under sterile and controlled conditions, using in vitro medium in the case of experiments related to cadmium exposure and using perlite as a soil-similar substrate for testing epoxiconazole. A phenotyping based on plantlets observations and physiological measurements under cadmium and epoxiconazole stress: i) characteristic symptoms (chloroses), ii) root and shoot growth and iii) biomass was performed at vegetative stage, in complementarity with the targeted metabolomic approach. Different levels of stress were tested on oilseed rape plantlets through dose-response experiments in order to obtain a concentration gradient representing defined stress conditions (i.e. low, middle and severe). With respect to cadmium stress, the concentration of Cd and sulfur (S) has been also measured in the different plant organs such as roots and shoots. GSL profile and content in plantlet organs were also investigated in order to highlight their putative involvement in Cd stress tolerance. About epoxiconazole stress, a characterisation of molecule concentration in the plantlets was carried out before studying its impact on terpenes profiles and on the breakdown products of GSLs (i.e. isothiocyanates) as putative metabolic markers.
Overall results showed that metabolic markers could be identified for both kinds of stress such as cadmium and epoxiconazole. These molecules were also involved in adaptive response of plantlets to stress. The sesquiterpenes clearly emerged from the experiments as VOC stress markers. In addition, the role of GSLs in the mechanisms of Cd-tolerance was highlighted with an emphasis on importance of oilseed rape primary S metabolism.
The non-invasive method of rapid analysis of VOCs emitted by oilseed rape plantlets and terpenes quantitation could certainly be used for studying the relationships between plant-emitted VOCs and other abiotic or biotic stresses. Finally, this customised glass chambers system could be used in regards to other plants such as potatoes, sugar beets and vegetable crops using soil substrate in order to discover new putative metabolic markers.
