title: Tracing cationic nutrients from xylem into stem tissue of French bean by stable isotope tracers and cryo-secondary ion mass spectrometry.
abstract: Fluxes of mineral nutrients in the xylem are strongly influenced by interactions with the surrounding stem tissues and are probably regulated by them. Toward a mechanistic understanding of these interactions, we applied stable isotope tracers of magnesium, potassium, and calcium continuously to the transpiration stream of cut bean (Phaseolus vulgaris) shoots to study their radial exchange at the cell and tissue level with stem tissues between pith and phloem. For isotope localization, we combined sample preparation with secondary ion mass spectrometry in a completely cryogenic workflow. After 20 min of application, tracers were readily detectable to various degrees in all tissues. The xylem parenchyma near the vessels exchanged freely with the vessels, its nutrient elements reaching a steady state of strong exchange with elements in the vessels within 20 min, mainly via apoplastic pathways. A slow exchange between vessels and cambium and phloem suggested that they are separated from the xylem, parenchyma, and pith, possibly by an apoplastic barrier to diffusion for nutrients (as for carbohydrates). There was little difference in these distributions when tracers were applied directly to intact xylem via a microcapillary, suggesting that xylem tension had little effect on radial exchange of these nutrients and that their movement was mainly diffusive.
authors: Central Division of Analytical Chemistry and Phytosphere Institute (ICG-3), Forschungszentrum Jülich, 52425 Juelich, Germany. r.metzner@fz-juelich.de
authors: Ralf
authors: R
authors: Metzner
authors: Heike Ursula
authors: HU
authors: Schneider
authors: Uwe
authors: U
authors: Breuer
authors: Michael Robert
authors: MR
authors: Thorpe
authors: Ulrich
authors: U
authors: Schurr
authors: Walter Heinz
authors: WH
authors: Schroeder
mesh_terms: D001692:Biological Transport; D020285:Cryoelectron Microscopy; D007554:Isotopes / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D027805:Phaseolus / Q000737:chemistry*; D018547:Plant Stems / Q000648:ultrastructure; D018526:Plant Transpiration; D018629:Spectrometry, Mass, Secondary Ion / Q000379:methods*; D052584:Xylem / Q000737:chemistry*
chemical_list: D007554:Isotopes