Contrasting dynamics of water and mineral nutrients in stems shown by stable isotope tracers and cryo-SIMS.
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.
Metzner
Ralf
R
Central Division of Analytical Chemistry, Forschungszentrum Jülich, Leo Brandt Strasse, 52425 Jülich, Germany. r.metzner@fz-juelich.de
Thorpe
Michael R
MR
Breuer
Uwe
U
Blümler
Peter
P
Schurr
Ulrich
U
Schneider
Heike U
HU
Schroeder
Walter H
WH
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
D007554:Isotopes; D014867:Water