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Caractérisation de la rhizodéposition du maïs (Zea mays L.) en réponse à la présence d’hydrocarbures aromatiques polycycliques et d’éléments traces métalliques

Abstract : This thesis focuses on the functioning of the rhizosphere in the context of revegetation of contaminated soils. We evaluated the impact of model contaminants (phenanthrene and cadmium) on maize (Zea mays L.) rhizodeposition to better understand the role of rhizodeposition in the plant's tolerance to this type of abiotic stress. To this end, a system of plant cultivation and rhizodeposit collection was set up to assess the response of maize to pollutant exposure. Our methodological development aimed at placing the plants in conditions as close as possible as those of soil cultivation, while allowing the collection of the two main families of rhizodeposits: root exudates and mucilage. Tools for characterizing the collected rhizodeposits were developed (colorimetric analyses, LC-MS, GC-MS) in order to determine the main families of compounds emitted by roots such as carbohydrates, amino acids, proteins and organic acids. Finally, the role of the molecules highlighted in our experiments on pollutant dynamics was discussed. This study revealed changes in the metabolic profile of rhizodeposition in presence of pollutants and those differences may vary considering the nature of the pollutant (organic or metallic). Cd caused a decrease of almost all compound emissions by maize roots (total carbon, carbohydrates, amino acids). Only proteins did not appear to be affected by the presence of the metal, while the exudation of organic acids increased with Cd exposure. Phenanthrene, on the other hand, increased the quantity of exuded carbon while it decreased the carbon secreted in the mucilage. In addition, it induced an increase in the emission of simple and polymerized carbohydrates, fatty acids and proteins while diffused organic acids decreased. In addition to the presence of pollutants, the development of maize was studied by analysing its rhizodeposition at the 4, 6 and 8-leaf stages. The effect of Cd on exudation seemed to increase from the 6-leaf stage, while that of phenanthrene tended to decrease. On the other hand, the influence of pollutants on mucilage seemed less marked and more constant over time. Finally, many rhizodeposited molecules have been identified as playing a role in the pollutants’ dynamics in the soil and therefore in their tolerance by the plant, in particular through complexation or solubilisation mechanisms.
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Clémentine Lapie. Caractérisation de la rhizodéposition du maïs (Zea mays L.) en réponse à la présence d’hydrocarbures aromatiques polycycliques et d’éléments traces métalliques. Agronomie. Université de Lorraine, 2019. Français. ⟨NNT : 2019LORR0237⟩. ⟨tel-02553673⟩

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