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Published on April 15, 2009; 10.1104/pp.108.131458

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Received October 20, 2008
Accepted April 11, 2009

Aquaporin-mediated reduction in maize root hydraulic conductivity impacts cell turgor and leaf elongation even without changing transpiration

Christina Ehlert , Christophe Maurel , Francois Tardieu , and Thierry Simonneau *

Laboratoire d'Ecophysiologie des Plantes sous Stress Environnementaux, UMR759 INRA/Montpellier SupAgro, 2, place Viala, 34060 Montpellier, France; Biochimie et Physiologie Moleculaire des Plantes, UMR5004 CNRS / UMR0386 INRA/Montpellier SupAgro/Universite Montpellier 2, 2, place Viala, 34060 Montpellier, France

* Corresponding author; email: thierry.simonneau{at}supagro.inra.fr.

Root hydraulic conductivity in plants (Lpr) exhibits large variations in response to abiotic stimuli. In this study, we investigated the impact of dynamic, aquaporin-mediated changes of Lpr on leaf growth, water potential and water flux throughout the plant. For this, we manipulated Lpr by subjecting roots to four independent treatments, with aquaporin inhibitors applied either to transpiring maize (Zea mays L.) plants grown in hydroponics or to de-topped root systems for estimation of Lpr. The treatments were acid load at pH 6.0 and pH 5.0, H2O2 and anoxia applied for one to two hours and subsequently reversed. First, we established that acid load affected cell hydraulic conductivity in maize root cortex. Lpr was reduced by all treatments by 31 to 63 %, with half times of about 15 min, and partly recovered when treatments were reversed. Cell turgor measured in the elongating zone of leaves decreased synchronously with Lpr and leaf elongation rate closely followed these changes across all treatments in a dose-dependent manner. Leaf and xylem water potentials also followed changes in Lpr. Stomatal conductance and rates of transpiration and water uptake were not affected by Lpr reduction under low evaporative demand. Increased evaporative demand, when combined with acid load at pH 6.0, induced stomatal closure and amplified all other responses without altering their synchrony. Root pressurization reversed the impact of acid load or anoxia on leaf elongation rate and water potential, further indicating that changes in turgor mediated the response of leaf growth to reductions in Lpr.






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