title: Contrasting dynamics of water and mineral nutrients in stems shown by stable isotope tracers and cryo-SIMS.
abstract: Lateral exchange of water and nutrients between xylem and surrounding tissues helps to de-couple uptake from utilization in all parts of a plant. We studied the dynamics of these exchanges, using stable isotope tracers for water (H(2)(18)O), magnesium ((26)Mg), potassium ((41)K) and calcium ((44)Ca) delivered via a cut stem for various periods to the transpiration stream of bean shoots (Phaseolus vulgaris cv. Fardenlosa Shiny). Tracers were subsequently mapped in stem cross-sections with cryo-secondary ion mass spectrometry. The water tracer equilibrated within minutes across the entire cross-section. In contrast, the nutrient tracers showed a very heterogeneous exchange between xylem vessels and the different stem tissues, even after 4 h. Dynamics of nutrients in the tissues revealed a fast and extensive exchange of nutrients in the xylem parenchyma, with, for example, calcium being completely replaced by tracer in less than 5 min. Dilution of potassium tracer during its 30 s transit in xylem sap through the stem showed that potassium concentration was up-regulated over many hours, to the extent that some of it was probably supplied by phloem recirculation from the shoot.
authors.affiliation: Central Division of Analytical Chemistry, Forschungszentrum Jülich, Leo Brandt Strasse, 52425 Jülich, Germany. r.metzner@fz-juelich.de
authors.forename: Ralf
authors.initials: R
authors.lastname: Metzner
authors.forename: Michael R
authors.initials: MR
authors.lastname: Thorpe
authors.forename: Uwe
authors.initials: U
authors.lastname: Breuer
authors.forename: Peter
authors.initials: P
authors.lastname: Blümler
authors.forename: Ulrich
authors.initials: U
authors.lastname: Schurr
authors.forename: Heike U
authors.initials: HU
authors.lastname: Schneider
authors.forename: Walter H
authors.initials: WH
authors.lastname: Schroeder
mesh_terms: D007554:Isotopes / Q000032:analysis; D027805:Phaseolus / Q000378:metabolism* / Q000502:physiology; D018547:Plant Stems / Q000378:metabolism / Q000502:physiology; D018526:Plant Transpiration; D014867:Water / Q000378:metabolism*; D052584:Xylem / Q000378:metabolism* / Q000502:physiology
chemical_list: D007554:Isotopes; D014867:Water