Plasma membrane aquaporins are involved in winter embolism recovery in walnut tree.
In perennial plants, freeze-thaw cycles during the winter months can induce the formation of air bubbles in xylem vessels, leading to changes in their hydraulic conductivity. Refilling of embolized xylem vessels requires an osmotic force that is created by the accumulation of soluble sugars in the vessels. Low water potential leads to water movement from the parenchyma cells into the xylem vessels. The water flux gives rise to a positive pressure essential for the recovery of xylem hydraulic conductivity. We investigated the possible role of plasma membrane aquaporins in winter embolism recovery in walnut (Juglans regia). First, we established that xylem parenchyma starch is converted to sucrose in the winter months. Then, from a xylem-derived cDNA library, we isolated two PIP2 aquaporin genes (JrPIP2,1 and JrPIP2,2) that encode nearly identical proteins. The water channel activity of the JrPIP2,1 protein was demonstrated by its expression in Xenopus laevis oocytes. The expression of the two PIP2 isoforms was investigated throughout the autumn-winter period. In the winter period, high levels of PIP2 mRNA and corresponding protein occurred simultaneously with the rise in sucrose. Furthermore, immunolocalization studies in the winter period show that PIP2 aquaporins were mainly localized in vessel-associated cells, which play a major role in controlling solute flux between parenchyma cells and xylem vessels. Taken together, our data suggest that PIP2 aquaporins could play a role in water transport between xylem parenchyma cells and embolized vessels.
Sakr
Soulaiman
S
Unité Mixte de Recherche 547-Physiologie Integreé de d'Arbre Fruitier Institut National de la Recherche Agronomique, Site des Cézeaux, Université Blaise Pascal, 24 Avenue des Landais, 63177 Aubière cedex, France. Soulaiman.Sakr@piaf.univ-bpclermont.fr
Alves
Georges
G
Morillon
Raphaël
R
Maurel
Karine
K
Decourteix
Mélanie
M
Guilliot
Agnès
A
Fleurat-Lessard
Pierrette
P
Julien
Jean-Louis
JL
Chrispeels
Maarten J
MJ
D000595:Amino Acid Sequence; D020346:Aquaporins / Q000502:physiology*; D002241:Carbohydrates / Q000032:analysis; D002352:Carrier Proteins / Q000737:chemistry / Q000502:physiology; D002462:Cell Membrane / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins; D031324:Juglans / Q000502:physiology*; D008969:Molecular Sequence Data; D010935:Plant Diseases; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000502:physiology; D012621:Seasons; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000737:chemistry / Q000502:physiology
D020346:Aquaporins; D002241:Carbohydrates; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; C430457:PAK1IP1 protein, human; C100530:PIP2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors