Abstract :

As in other multicellular organs, leaf and fruit growth and development are characterised by the coordination of cell division and expansion, which are major growth processes. Cells in the pericarp of the fleshy fruit also undergo successive endocycles resulting in a significant increase in cell ploidy. There is a clear link between cell growth and endoreduplication, however, this is still poorly understood from a functional point of view. Cellular processes interact strongly during organ development and are linked to carbon and water flows in the plant. The objective of this thesis is to better understand the multi-scale control of leaf and fruit growth in tomato (Solanum lycopersicum Mill.) and the plasticity of their growth in response to soil water stress. The study focused on the cherry tomato genotype Solanum lycopersicum, cv.West Virginia 106 (WVa 106) which was grown under different irrigation conditions using automated systems developed for this study. The response to soil water deficit was studied at different scales of observation, (tissue, organ, whole plant) and at different stages of plant growth by adapting protocols used so far for determinate growth plants and single leaves. Two transgenic genotypes modified on a cell cycle regulation gene were also grown in order to vary the traits related to cell growth and better understand their links. The growth kinetics of the source and sink organs, i.e. the leaf and the fruit, at the cellular and tissue levels were also described. The results provided new information on the coordinations between the various processes studied and confirmed hypotheses already present in the literature. This work provided an original data set on the effects of water stress on the cellular processes (division, expansion, endoreduplication) involved in leaf and fruit growth in tomato, and enabled us to better understand their interactions on a larger scale, the plant as a whole. In terms of prospects, this data set could be used to develop a development model for fleshy fruit under optimal conditions and to test its genericity on another organ, the leaf. It opens up avenues for reflection on the modelling of plant plasticity in response to water stress.