In plants, water deficit causes morphological, molecular and physiological responses, including stomata closure, photosynthesis reduction and accumulation of cellular osmoprotective compounds such as proline. This amino acid influences important biological functions, for instance by helping the stabilization of proteins and intracellular membranes and by mitigating the negative effects of reactive oxygen species. The present work had the objective to evaluate the performance of two transgenic events (Ev.6 and Ev.8) of Swingle citrumelo (Citrus paradisi Macfad. cv. Duncan x Poncirus trifoliata L. Raf.) rootstock transformed with the mutant Vigna aconitifolia P5CS-F129A gene, which encodes the key enzyme Î1-pyrroline-5-carboxylate synthetase (P5CS) for proline biosynthesis, under the control of the stress-responsive RD29A promoter. Under greenhouse conditions, plants were left without irrigation up to reach severe stress level and then rehydrated after 31 days without watering. The event 8 (Ev.8) displayed significant increments of proline and higher photosynthesis, transpiration and stomata conductance rate throughout the stress period. Thus, because of its overall drought response, the plant 1329 of the Ev.8 was selected for multiplication and future field competition tests under our citrus rootstock breeding program, aiming to select a Swingle citrumelo genotype more tolerant to water deficit.