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WHOLE PLANT AND ECOPHYSIOLOGY

Aquaporin-Mediated Reduction in Maize Root Hydraulic Conductivity Impacts Cell Turgor and Leaf Elongation Even without Changing Transpiration^1,[W]

Laboratoire d'Ecophysiologie des Plantes sous Stress Environnementaux, UMR759 INRA/Montpellier SupAgro, 34060 Montpellier, France (C.E., F.T., T.S.); and Biochimie et Physiologie Moléculaire des Plantes, UMR5004 CNRS/UMR0386 INRA/Montpellier SupAgro/Université Montpellier 2, 34060 Montpellier, France (C.M.)

Root hydraulic conductivity in plants (Lp_r) exhibits large variations in response to abiotic stimuli. In this study, we investigated the impact of dynamic, aquaporin-mediated changes of Lp_r on leaf growth, water potential, and water flux throughout the plant. For this, we manipulated Lp_r by subjecting roots to four independent treatments, with aquaporin inhibitors applied either to transpiring maize (Zea mays) plants grown in hydroponics or to detopped root systems for estimation of Lp_r. The treatments were acid load at pH 6.0 and 5.0 and hydrogen peroxide and anoxia applied for 1 to 2 h and subsequently reversed. First, we established that acid load affected cell hydraulic conductivity in maize root cortex. Lp_r 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 Lp_r, 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 Lp_r. Stomatal conductance and rates of transpiration and water uptake were not affected by Lp_r 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 Lp_r.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Thierry Simonneau (thierry.simonneau{at}supagro.inra.fr).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.131458

^* Corresponding author; e-mail thierry.simonneau{at}supagro.inra.fr.

Received October 20, 2008; accepted April 11, 2009; published April 15, 2009.