Résumé
Plant growth relies on C metabolism because carbohydrates fuel main metabolic pathways for the build-up of structures, for ATP production, and exert some transcriptional control on the metabolic and developmental machinery. When plants are exposed to drought, both growth and C management are affected leading to the simple idea that growth changes could be triggered by C metabolism and partitioning changes. We tested this idea in the model plant Arabidopsis - At the whole plant level, leaf expansion is reduced while photosynthesis is maintained leading to C compounds accumulation, in particular organic acids, which contribute to osmotic adjustment while C export to roots is promoted. These changes occur in the absence of major reprogramming of C metabolism (as seen by the analysis of 30 enzymes) and contribute to the improvement of C status (as seen by the expression of sugar responsive genes). - At the single leaf level, the expansion of young visible leaves show strong night growth depressions in a series of mutants impaired in starch management in phase with the fluctuations of their C status. Drought improves the C status of these mutants at night and releases the relationship between C availability and growth. - At the root level, elongation that was earlier found to be tightly related to the hexose content in the root tip vanishes under drought suggesting that C flux and utilization become uncoupled. Together, these data suggest that drought affects C metabolism and partitioning mainly as a consequence of growth changes