title: Influence of nitrogen fertilization on xylem traits and aquaporin expression in stems of hybrid poplar.
abstract: We studied the influence of nitrogen (N) on hydraulic traits and aquaporin (AQP) expression in the stem xylem of hybrid poplar saplings (Populus trichocarpa (Torr. & Gray) x deltoides Bartr. ex Marsh clone H11-11). Plants were grown in a controlled environment and were kept well watered throughout the experiments. Hydraulic measurements were done on basal and distal stem segments of plants receiving high N fertilization (high N plants) versus plants receiving only adequate N fertilization (adequate N plants). High N plants grew faster and exhibited more leaf area than adequate N controls. These morphological differences were paralleled by wider vessels and higher specific conductivities (K(S)) in high N plants. However, stems of high N plants were more vulnerable to xylem cavitation, at least in one of two experiments, and showed lower wood densities than stems of adequate N plants. Leaf area was strongly correlated with cross-sectional xylem area in both plant groups. Since higher K(S) in high N plants was accompanied by concomitant increases in leaf area, leaf-specific conductivities were similar in both plant groups. Influences of N on hydraulic traits were paralleled by changes in AQP expression. Seven AQPs were upregulated in the stem xylem of high N plants, five of which have been identified recently as water transporters. The enhanced growth of secondary xylem of high N plants has been shown to result from both increased cambial activity as well as increased cell size. We suggest that some of these water-transporting AQPs could play a role in xylogenesis, facilitating the influx of water into the zone of differentiating and maturing cells in secondary xylem, including expanding vessels.
authors.affiliation: Department of Renewable Resources, University of Alberta, Edmonton, AB, T6G 2E3, Canada. uwe.hacke@ualberta.ca
authors.forename: Uwe G
authors.initials: UG
authors.lastname: Hacke
authors.forename: Lenka
authors.initials: L
authors.lastname: Plavcová
authors.forename: Adriana
authors.initials: A
authors.lastname: Almeida-Rodriguez
authors.forename: Susanne
authors.initials: S
authors.lastname: King-Jones
authors.forename: Wenchun
authors.initials: W
authors.lastname: Zhou
authors.forename: Janice E K
authors.initials: JE
authors.lastname: Cooke
mesh_terms: D020346:Aquaporins / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects*; D009584:Nitrogen / Q000494:pharmacology*; D032107:Populus / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D014867:Water / Q000378:metabolism; D052584:Xylem / Q000187:drug effects / Q000502:physiology*
chemical_list: D020346:Aquaporins; D014867:Water; D009584:Nitrogen