title: Immunolabelling of intervessel pits for polysaccharides and lignin helps in understanding their hydraulic properties in Populus tremula × alba.
abstract: OBJECTIVE
  The efficiency and safety functions of xylem hydraulics are strongly dependent on the pits that connect the xylem vessels. However, little is known about their biochemical composition and thus about their hydraulic properties. In this study, the distribution of the epitopes of different wall components (cellulose, hemicelluloses, pectins and lignins) was analysed in intervessel pits of hybrid poplar (Populus tremula × alba).
  
  
  METHODS
  Immunogold labelling with transmission electron microscopy was carried out with a set of antibodies raised against different epitopes for each wall polysaccharide type and for lignins. Analyses were performed on both immature and mature vessels. The effect of sap ionic strength on xylem conductance was also tested.
  
  
  RESULTS
  In mature vessels, the pit membrane (PM) was composed of crystalline cellulose and lignins. None of the hemicellulose epitopes were found in the PM. Pectin epitopes in mature vessels were highly concentrated in the annulus, a restricted area of the PM, whereas they were initially found in the whole PM in immature vessels. The pit border also showed a specific labelling pattern, with higher cellulose labelling compared with the secondary wall of the vessel. Ion-mediated variation of 24 % was found for hydraulic conductance.
  
  
  CONCLUSIONS
  Cellulose microfibrils, lignins and annulus-restricted pectins have different physicochemical properties (rigidity, hydrophobicity, porosity) that have different effects on the hydraulic functions of the PM, and these influence both the hydraulic efficiency and vulnerability to cavitation of the pits, including ion-mediated control of hydraulic conductance. Impregnation of the cellulose microfibrils of the PM with lignins, which have low wettability, may result in lower cavitation pressure for a given pore size and thus help to explain the vulnerability of this species to cavitation.
authors.affiliation: Clermont Université, Université Blaise Pascal, UMR547 PIAF, BP 10448, F-63000 Clermont-Ferrand, France, INRA, UMR547 PIAF, F-63100 Clermont-Ferrand, France and INRA, UR1268 Biopolymers Interactions Assemblies, BP 71627, F-44316 Nantes, France Clermont Université, Université Blaise Pascal, UMR547 PIAF, BP 10448, F-63000 Clermont-Ferrand, France, INRA, UMR547 PIAF, F-63100 Clermont-Ferrand, France and INRA, UR1268 Biopolymers Interactions Assemblies, BP 71627, F-44316 Nantes, France stephane.herbette@univ-bpclermont.fr.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Herbette
authors.affiliation: Clermont Université, Université Blaise Pascal, UMR547 PIAF, BP 10448, F-63000 Clermont-Ferrand, France, INRA, UMR547 PIAF, F-63100 Clermont-Ferrand, France and INRA, UR1268 Biopolymers Interactions Assemblies, BP 71627, F-44316 Nantes, France.
authors.forename: Brigitte
authors.initials: B
authors.lastname: Bouchet
authors.affiliation: Clermont Université, Université Blaise Pascal, UMR547 PIAF, BP 10448, F-63000 Clermont-Ferrand, France, INRA, UMR547 PIAF, F-63100 Clermont-Ferrand, France and INRA, UR1268 Biopolymers Interactions Assemblies, BP 71627, F-44316 Nantes, France Clermont Université, Université Blaise Pascal, UMR547 PIAF, BP 10448, F-63000 Clermont-Ferrand, France, INRA, UMR547 PIAF, F-63100 Clermont-Ferrand, France and INRA, UR1268 Biopolymers Interactions Assemblies, BP 71627, F-44316 Nantes, France.
authors.forename: Nicole
authors.initials: N
authors.lastname: Brunel
authors.affiliation: Clermont Université, Université Blaise Pascal, UMR547 PIAF, BP 10448, F-63000 Clermont-Ferrand, France, INRA, UMR547 PIAF, F-63100 Clermont-Ferrand, France and INRA, UR1268 Biopolymers Interactions Assemblies, BP 71627, F-44316 Nantes, France.
authors.forename: Estelle
authors.initials: E
authors.lastname: Bonnin
authors.affiliation: Clermont Université, Université Blaise Pascal, UMR547 PIAF, BP 10448, F-63000 Clermont-Ferrand, France, INRA, UMR547 PIAF, F-63100 Clermont-Ferrand, France and INRA, UR1268 Biopolymers Interactions Assemblies, BP 71627, F-44316 Nantes, France Clermont Université, Université Blaise Pascal, UMR547 PIAF, BP 10448, F-63000 Clermont-Ferrand, France, INRA, UMR547 PIAF, F-63100 Clermont-Ferrand, France and INRA, UR1268 Biopolymers Interactions Assemblies, BP 71627, F-44316 Nantes, France.
authors.forename: Hervé
authors.initials: H
authors.lastname: Cochard
authors.affiliation: Clermont Université, Université Blaise Pascal, UMR547 PIAF, BP 10448, F-63000 Clermont-Ferrand, France, INRA, UMR547 PIAF, F-63100 Clermont-Ferrand, France and INRA, UR1268 Biopolymers Interactions Assemblies, BP 71627, F-44316 Nantes, France.
authors.forename: Fabienne
authors.initials: F
authors.lastname: Guillon
mesh_terms: D001704:Biopolymers / Q000378:metabolism*; D002473:Cell Wall / Q000378:metabolism* / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D011134:Polysaccharides / Q000378:metabolism*; D032107:Populus / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D013194:Staining and Labeling; D052584:Xylem / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D001704:Biopolymers; D011134:Polysaccharides
keywords: Populus tremula × alba; annulus; cavitation; cellulose; hydraulic conductance; immunolabelling; lignin; pectin; pit membrane; plant water relations; sap flow; xylem