Circadian rhythms enable plants to anticipate daily environmental variations, resulting in growth oscillations under continuous light. Because plants daily transpire up to 200% of their water content, their water status oscillates from favourable during the night to unfavourable during the day. We show that rhythmic leaf growth under continuous light is observed in plants that experience large alternations of water status during an entrainment period, but is considerably buffered otherwise. Measurements and computer simulations show that this is due to oscillations of plant hydraulic conductance and plasma membrane aquaporin messenger RNA abundance in roots during continuous light. A simulation model suggests that circadian oscillations of root hydraulic conductance contribute to acclimation to water stress by increasing root water uptake, thereby favouring growth and photosynthesis. They have a negative effect in favourable hydraulic conditions. Climate-driven control of root hydraulic conductance therefore improves plant performances in both stressed and non-stressed conditions.
Bibliographical noteFunding Information:
This work was supported by the EU project FP7-244374 (DROPS), the ANR-08-GENM-003 project and the Région Languedoc-Roussillon, together with the Interuniversity Attraction Poles Programme-Belgian Science Policy (IAP7/29) and the Belgian French community ARC11/16-036 project. We thank M Bosio, JP Pichon, A Clementi and S Praud (Biogemma) for their contributions to the transcriptome analysis and for seeds of NCED plants. Field experiments were carried out at Nerac and Karlsruhe by Biogemma and KWS, respectively, in the context of DROPS. Meteorological data were compiled and cleaned by E. Millet and C. Welcker (INRA LEPSE).