title: Winter variation in xylem sap pH of walnut trees: involvement of plasma membrane H+-ATPase of vessel-associated cells.
abstract: We studied seasonal variation in xylem sap pH of Juglans regia L. Our main objectives were to (1) test the effect of temperature on seasonal changes in xylem sap pH and (2) study the involvement of plasma membrane H+-ATPase of vessel-associated cells in the control of sap pH. For this purpose, orchard-grown trees were compared with trees grown in a heated (> or = 15 degrees C) greenhouse. During autumn, sap pH was not directly influenced by temperature. A seasonal change in H+-ATPase activity resulting from seasonal variation in the amount of protein was measured in orchard-grown trees, whereas no significant seasonal changes were recorded in greenhouse-grown trees. Our data suggest that H+-ATPase does not regulate xylem sap pH directly by donating protons to the xylem, but by facilitating secondary active H+/sugar transport, among other mechanisms.
authors.affiliation: U.M.R. PIAF, site des Cézeaux, Université Blaise Pascal, 24 avenue des Landais, 63177 Aubière cedex, France.
authors.forename: Georges
authors.initials: G
authors.lastname: Alves
authors.forename: Thierry
authors.initials: T
authors.lastname: Ameglio
authors.forename: Agnes
authors.initials: A
authors.lastname: Guilliot
authors.forename: Pierrette
authors.initials: P
authors.lastname: Fleurat-Lessard
authors.forename: André
authors.initials: A
authors.lastname: Lacointe
authors.forename: Soulaïman
authors.initials: S
authors.lastname: Sakr
authors.forename: Gilles
authors.initials: G
authors.lastname: Petel
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Julien
mesh_terms: D006863:Hydrogen-Ion Concentration; D031324:Juglans / Q000201:enzymology / Q000502:physiology*; D006180:Proton-Translocating ATPases / Q000502:physiology*; D012621:Seasons; D014197:Trees / Q000201:enzymology / Q000502:physiology*
chemical_list: D006180:Proton-Translocating ATPases