Plants respond to environmental stress by dynamically reprogramming their growth. Whereas stress onset is accompanied by rapid growth inhibition leading to smaller organs, growth will recover and adapt once the stress conditions become stable and do no threaten plant survival. Here, adaptation of growing Arabidopsis thaliana leaves to mild and prolonged osmotic stress was investigated by means of a complete metabolic labeling strategy with the (15)N-stable isotope as a complement to a previously published transcript and metabolite profiling. Global analysis of protein changes revealed that plastidial ATPase, Calvin cycle, and photorespiration were down-regulated, but mitochondrial ATP synthesis was up-regulated, indicating the importance of mitochondria in preserving plastid functions during water stress. Although transcript and protein data correlated well with the stable and prolonged character of the applied stress, numerous proteins were clearly regulated at the post-transcriptional level that could, at least partly, be related to changes in protein synthesis and degradation. In conclusion, proteomics using the (15)N labeling helped understand the mechanisms underlying growth adaptation to osmotic stress and allowed the identification of candidate genes to improve plant growth under limited water.