Gast ::
| Hauptseite > Publikationsdatenbank > The mechanisms of refilling of the xylem conduits and bleeding of tall birch during spring |
| Hauptseite > Publikationsdatenbank > The mechanisms of refilling of the xylem conduits and bleeding of tall birch during spring |
| Journal Article | PreJuSER-58850 |
; ; ; ; ; ; ; ; ; ; ; ;
2008
Wiley-Blackwell - STM
Oxford [u.a.] :Wiley- Blackwell
This record in other databases: 
Please use a persistent id in citations: doi:10.1111/j.1438-8677.2008.00062.x
Abstract: 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.
Keyword(s): Betula: physiology (MeSH) ; Carbohydrate Metabolism (MeSH) ; Electrolytes: metabolism (MeSH) ; Magnetic Resonance Spectroscopy (MeSH) ; Osmolar Concentration (MeSH) ; Osmotic Pressure (MeSH) ; Plant Roots: physiology (MeSH) ; Seasons (MeSH) ; Trees: physiology (MeSH) ; Water: physiology (MeSH) ; Xylem: physiology (MeSH) ; Electrolytes ; Water ; J ; Betula pendula (birch) (auto) ; lipids (auto) ; osmotic pressure gradients (auto) ; root pressure (auto) ; sap bleeding (auto) ; sugars (auto) ; xylem refilling (auto)
|
The record appears in these collections: |