title: 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.
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.
authors.affiliation: Laboratoire d'Ecophysiologie des Plantes sous Stress Environnementaux, UMR759 INRA/Montpellier SupAgro, 2, place Viala, 34060 Montpellier, France.
authors.forename: Christina
authors.initials: C
authors.lastname: Ehlert
authors.forename: Claude
authors.initials: C
authors.lastname: Plassard
authors.forename: Sarah Jane
authors.initials: SJ
authors.lastname: Cookson
authors.forename: François
authors.initials: F
authors.lastname: Tardieu
authors.forename: Thierry
authors.initials: T
authors.lastname: Simonneau
mesh_terms: D003681:Dehydration; D015536:Down-Regulation; D004338:Drug Combinations; D006863:Hydrogen-Ion Concentration; D008839:Microelectrodes; D009997:Osmotic Pressure; D018515:Plant Leaves / Q000187:drug effects / Q000254:growth & development / Q000502:physiology*; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism*; D020959:Polyethylene / Q000494:pharmacology; D011343:Procaine; D011422:Propionates / Q000494:pharmacology; D013312:Stress, Physiological; D003313:Zea mays / Q000187:drug effects / Q000502:physiology*
chemical_list: D004338:Drug Combinations; D011422:Propionates; D011343:Procaine; C037126:turigeran; D020959:Polyethylene; C029658:propionic acid