Temperature effects on xylem sap osmolarity in walnut trees: evidence for a vitalistic model of winter embolism repair.
We studied the effect of temperature on the carbohydrate status of parenchyma cells during winter in relation to the efflux and influx of sugars between parenchyma cells and xylem vessels in 1-year-old twigs of walnut (Juglans regia L.). The mechanism of sugar transfer between contact cells and vessels was also investigated. We obtained new insights into the possible osmotic role of sugars, particularly sucrose, in stem pressure formation and winter embolism repair. Accumulation of sucrose in the xylem sap during winter was mainly influenced by: (1) abundant conversion of starch to sucrose in the symplast at low temperatures; (2) sucrose efflux into the apoplast at low temperatures (1 degrees C); and (3) inefficient sugar uptake at low temperatures, although efficient sugar uptake occurred at 15 degrees C. We hypothesize that a diethyl pyrocarbonate (DEPC)-sensitive protein mediates facilitated diffusion of sucrose from parenchyma cells to xylem vessels (efflux) in walnut. We discuss the possible occurrence of active H+-sucrose symports and the coexistence of both influx and efflux processes in walnut in winter and the modulation of the relative importance of these flows by temperature.
Améglio
Thierry
T
U.M.R. PIAF (INRA - Université Blaise Pascal), Site INRA de Crouelle, 234 Avenue du Brezet, F-63039 Clermont-Ferrand Cedex 2, France. ameglio@clermont.inra.fr
Decourteix
Mélanie
M
Alves
Georges
G
Valentin
Vincent
V
Sakr
Soulaiman
S
Julien
Jean-Louis
JL
Petel
Gilles
G
Guilliot
Agnes
A
Lacointe
André
A
D002241:Carbohydrates / Q000502:physiology; D031324:Juglans / Q000502:physiology*; D008954:Models, Biological; D009994:Osmolar Concentration; D018547:Plant Stems / Q000502:physiology; D012621:Seasons; D013696:Temperature; D014197:Trees / Q000502:physiology*
D002241:Carbohydrates