Influence of copper nutrition on alfalfa cell wall differentiation through a proteomic approach

Plant cells are surrounded by a rigid frame, the so-called cell wall, which restricts cell expansion. The cell wall is a dynamic structure that provides the structural strength needed to allow upright growth of the plant and confers resistance to pathogens. In this thesis, the first objective is to disentangle the dynamism of the plant cell wall by a core proteomics study. This approach, which combines both gel-based and gel-free methods, is supported by a panel of molecular techniques among which fibre characterization, mineral analysis and targeted gene expression profiling. Since cell wall development and remodelling relies on cellular and extracellular processes, the classical total proteome analysis is complemented by a focused study of the cell wall proteome. These studies indicate that the stem cell wall has an active and highly adaptive metabolism which constantly evolves and recycles during development. Each stage of maturity has a unique cellular and extracellular protein profile. As second objective, we identify, using the same techniques, the effects of fertilisation with micronutrients on alfalfa stem development to assess if microelement application, especially copper, drives significant changes in the plant stem metabolism. Our results support the fact that copper application elicits general pathways of plant resistance and may prolong the juvenile status of the stem. However, a combined application of copper and zinc is detrimental for plant growth. Altogether this thesis provides an integrated overview of the molecular mechanisms occurring at the cellular and the extracellular level, and which are modulated with maturity and mineral availability.(AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 201