Effects of UV-C and hydrogen peroxide elicitation on the metabolism of two chilli genotypes ; Effets de l’élicitation par les UV-C et le peroxyde d’hydrogène sur le métabolisme de deux génotypes de piment

ID4FEED is a company based in Annecy (74), which contributes to the research and development of complementary feeds for farm animals based on plant extracts. Some natural plant compounds that strengthen the immune system of animals are particularly promising as alternatives to antibiotics, such as capsaicinoids and carotenoids. These two families of molecules are accumulated simultaneously and in significant quantities in plants of the genus Capsicum. Several biotic or abiotic stress factors modulate the biosynthetic fluxes of secondary plant metabolism and influence capsaicinoid and carotenoid concentrations in peppers in particular. Among the physical factors likely to stimulate the synthesis of these compounds of interest, UV-C radiation is currently being studied because it initiates molecularsignaling pathways that regulate secondary metabolism. During my thesis work, the effects of UV-C radiation, as well as H2O2, an oxidative intermediate of stress signaling pathways in plants, were studied on the synthesis and accumulation of carotenoids and capsaicinoids in fruits of two pepper genotypes. The first objective was to develop targeted profiling methods to assay the metabolites of interest, to identify the modalities of application of treatments capable of increasing these concentrations in the fruits of two chili genotypes, C. chinense 'Habanero' and C. frutescens 'Bhut Jolokia'. The safety of the stimulation treatments on the plants, which is fundamental for an industrially valid process, was systematically verified by measuring physiological markers from the induction curves of maximum chlorophyll fluorescence. As none of the applications were able to increase the carotenoid and capsaicinoid composition of the fruits, the response to UV-C of pepper plants at the vegetative stage was studied. Metabolomic approaches combining non-targeted and multi-targeted profiling in GC-MS and LC-MS/MS, coupled with data processing by molecular networks and multivariate statistics revealed a very marked protection of ...