Winter variation in xylem sap pH of walnut trees: involvement of plasma membrane H+-ATPase of vessel-associated cells.
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.
Alves
Georges
G
U.M.R. PIAF, site des Cézeaux, Université Blaise Pascal, 24 avenue des Landais, 63177 Aubière cedex, France.
Ameglio
Thierry
T
Guilliot
Agnes
A
Fleurat-Lessard
Pierrette
P
Lacointe
André
A
Sakr
Soulaïman
S
Petel
Gilles
G
Julien
Jean-Louis
JL
D006863:Hydrogen-Ion Concentration; D031324:Juglans / Q000201:enzymology / Q000502:physiology*; D006180:Proton-Translocating ATPases / Q000502:physiology*; D012621:Seasons; D014197:Trees / Q000201:enzymology / Q000502:physiology*
D006180:Proton-Translocating ATPases