Document Detail

The mechanisms of refilling of xylem conduits and bleeding of tall birch during spring.
MedLine Citation:
PMID:  18761499     Owner:  NLM     Status:  MEDLINE    
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.
M Westhoff; H Schneider; D Zimmermann; S Mimietz; A Stinzing; L H Wegner; W Kaiser; G Krohne; St Shirley; P Jakob; E Bamberg; F-W Bentrup; U Zimmermann
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Plant biology (Stuttgart, Germany)     Volume:  10     ISSN:  1435-8603     ISO Abbreviation:  Plant Biol (Stuttg)     Publication Date:  2008 Sep 
Date Detail:
Created Date:  2008-09-02     Completed Date:  2008-10-21     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  101148926     Medline TA:  Plant Biol (Stuttg)     Country:  Germany    
Other Details:
Languages:  eng     Pagination:  604-23     Citation Subset:  IM    
Lehrstuhl für Biotechnologie, Biozentrum, Universität Würzburg, Würzburg, Germany.
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MeSH Terms
Betula / physiology*
Carbohydrate Metabolism
Electrolytes / metabolism
Magnetic Resonance Spectroscopy
Osmolar Concentration
Osmotic Pressure
Plant Roots / physiology*
Trees / physiology*
Water / physiology*
Xylem / physiology*
Reg. No./Substance:
0/Electrolytes; 7732-18-5/Water

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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