TY  - JOUR
AU  - Westhoff, M.
AU  - Schneider, H.
AU  - Zimmermann, D.
AU  - Mimietz, S.
AU  - Stinzing, A.
AU  - Wegner, L. H.
AU  - Kaiser, W.
AU  - Krohne, G.
AU  - Shirley, St.
AU  - Jakob, P.
AU  - Bamberg, E.
AU  - Bentrup, F.-W.
AU  - Zimmermann, U.
TI  - The mechanisms of refilling of the xylem conduits and bleeding of tall birch during spring
JO  - Plant biology
VL  - 10
SN  - 1435-8603
CY  - Oxford [u.a.] :Wiley- Blackwell
PB  - Wiley-Blackwell - STM
M1  - PreJuSER-58850
SP  - 604 - 623
PY  - 2008
N1  - Record converted from VDB: 12.11.2012
AB  - Seasonal variations in osmolality and components of xylem sap in tall birch trees were determined using several techniques. Xylem sap was extracted from branch and trunk sections of 58 trees using the very rapid gas bubble-based jet-discharge method. The 5-cm long wood pieces were taken at short intervals over the entire tree height. The data show that large biphasic osmolality gradients temporarily exist within the conducting xylem conduits during leaf emergence (up to 272 mosmol x kg(-1) at the apex). These gradients (arising mainly from glucose and fructose) were clearly held within the xylem conduit as demonstrated by (1)H NMR imaging of intact twigs. Refilling experiments with benzene, sucrose infusion, electron and light microscopy, as well as (1)H NMR chemical shift microimaging provided evidence that the xylem of birch represents a compartment confined by solute-reflecting barriers (radial: lipid linings/lipid bodies; axial: presumably air-filled spaces). These features allow transformation of osmolality gradients into osmotic pressure gradients. Refilling of the xylem occurs by a dual mechanism: from the base (by root pressure) and from the top (by hydrostatic pressure generated by xylem-bound osmotic pressure). The generation of osmotic pressure gradients was accompanied by bleeding. Bleeding could be observed at a height of up to 21 m. Bleeding rates measured at a given height decreased exponentially with time. Evidence is presented that the driving force for bleeding is the weight of the static water columns above the bleeding point. The pressure exerted by the water columns and the bleeding volume depend on the water-filling status of (communicating) vessels.
KW  - Betula: physiology
KW  - Carbohydrate Metabolism
KW  - Electrolytes: metabolism
KW  - Magnetic Resonance Spectroscopy
KW  - Osmolar Concentration
KW  - Osmotic Pressure
KW  - Plant Roots: physiology
KW  - Seasons
KW  - Trees: physiology
KW  - Water: physiology
KW  - Xylem: physiology
KW  - Electrolytes (NLM Chemicals)
KW  - Water (NLM Chemicals)
KW  - J (WoSType)
LB  - PUB:(DE-HGF)16
C6  - pmid:18761499
UR  - <Go to ISI:>//WOS:000258288200009
DO  - DOI:10.1111/j.1438-8677.2008.00062.x
UR  - https://juser.fz-juelich.de/record/58850
ER  -