Role of trichomes and volatile organic compounds in ozone deposition and stress response of tomato plants ; Rôle des trichomes et des composés organiques volatils dans le dépôt d’ozone et la réponse des plantes de tomate au stress

Ozone (O3) is a greenhouse gas and an air pollutant that can, at high concentrations, significantly impact the growth and productivity of agricultural and forest ecosystems. However, the sensitivity of plants to O3 differs according to their ecophysiological, morphological and biochemical characteristics. In my PhD work, I have sought to improve our understanding of resistance of tomatoes to ozone, in particular through the properties of trichomes which are reservoirs of VOCs capable of reacting with ozone. The research strategy consisted in analyzing the variability of VOC emissions and their origins in the 8 parent genotypes of the MAGIC TOM population with high genetic variability. This study mainly highlighted the low constitutive emissions of tomato. It was followed by micro-morphological and histochemical analysis of trichomes on parents and their associated mutants to analyze their role in ozone depletion and plant resistance. Wild parents and their associated mutants were contrasted in trichome composition, morphology, type and density. I have measured the main ozone deposition (cuticular, stomatal, and chemical) through the gas-phase reaction of VOCs with ozone. Plant responses to oxidative stress were measured through changes in photosynthesis, stomatal conductance, Fv/Fm ratio and quantification of visible damage, as well as measurements of VOC emissions during and after exposure to different ozone concentrations. Plant responses differed according to the phenotypes analyzed. Overall, photosynthetic falls, VOC LOX were formed and physical damages were observed in response to oxidative stress. Our results underline the weak role of VOCs in ozone destruction by gas phase reaction and outline the role of the density of glandular and non glandular trichomes in plant resistance. In addition, the resistance to ozone observed in a mutant deficient in numerous monoterpenes and sesquiterpenes suggests that other secondary metabolites with high reactivity and ability to cope with oxidative stress are involved. ...