Do pH changes in the leaf apoplast contribute to rapid inhibition of leaf elongation rate by water stress? Comparison of stress responses induced by polyethylene glycol and down-regulation of root hydraulic conductivity

Authors

  • CHRISTINA EHLERT,

    1. Laboratoire d'Ecophysiologie des Plantes sous Stress Environnementaux, UMR759 INRA/Montpellier SupAgro, 2, place Viala, 34060 Montpellier, France
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    • Current address: European Food Safety Authority (EFSA), Largo N. Palli 5/a, 43121 Parma, Italy.

  • CLAUDE PLASSARD,

    1. Ecologie Fonctionnelle & Biogéochimie des Sols, UMR1222 INRA/IRD/Montpellier SupAgro, 2, place Viala, 34060 Montpellier, France
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  • SARAH JANE COOKSON,

    1. Ecophysiologie et Génomique Fonctionnelle de la Vigne, UMR1287 Institut des Sciences de la Vigne et du Vin, 210 Chemin de Leysotte, CS 50008, 33883 Villenave d'Ornon, France
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  • FRANÇOIS TARDIEU,

    1. Laboratoire d'Ecophysiologie des Plantes sous Stress Environnementaux, UMR759 INRA/Montpellier SupAgro, 2, place Viala, 34060 Montpellier, France
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  • THIERRY SIMONNEAU

    Corresponding author
    1. Laboratoire d'Ecophysiologie des Plantes sous Stress Environnementaux, UMR759 INRA/Montpellier SupAgro, 2, place Viala, 34060 Montpellier, France
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  • This work was supported by a doctoral fellowship from INRA to C.E., and grant ANR-05-GPLA-034-02 from the French Agence Nationale de la Recherche to F.T. and T.S.

T. Simonneau. Fax: +33 4 67 52 21 16; e-mail: thierry.simonneau@supagro.inra.fr

ABSTRACT

We have dissected the influences of apoplastic pH and cell turgor on short-term responses of leaf growth to plant water status, by using a combination of a double-barrelled pH-selective microelectrodes and a cell pressure probe. These techniques were used, together with continuous measurements of leaf elongation rate (LER), in the (hidden) elongating zone of the leaves of intact maize plants while exposing roots to various treatments. Polyethylene glycol (PEG) reduced water availability to roots, while acid load and anoxia decreased root hydraulic conductivity. During the first 30 min, acid load and anoxia induced moderate reductions in leaf growth and turgor, with no effect on leaf apoplastic pH. PEG stopped leaf growth, while turgor was only partially reduced. Rapid alkalinization of the apoplast, from pH 4.9 ± 0.3 to pH 5.8 ± 0.2 within 30 min, may have participated to this rapid growth reduction. After 60 min, leaf growth inhibition correlated well with turgor reduction across all treatments, supporting a growth limitation by hydraulics. We conclude that apoplastic alkalinization may transiently impair the control of leaf growth by cell turgor upon abrupt water stress, whereas direct hydraulic control of growth predominates under moderate conditions and after a 30–60 min delay following imposition of water stress.

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