Document Detail

During measurements of root hydraulics with pressure probes, the contribution of unstirred layers is minimized in the pressure relaxation mode: comparison with pressure clamp and high-pressure flowmeter.
MedLine Citation:
PMID:  17547656     Owner:  NLM     Status:  MEDLINE    
The effects of unstirred layers (USLs) at the endodermis of roots of young maize plants (Zea mays L.) were quantified, when measuring the water permeability of roots using a root pressure probe (RPP) in the pressure relaxation (PR) and pressure clamp (PC) modes. Different from PRs, PCs were performed by applying a constant pressure for certain periods of time. Experimental data were compared with results from simulations based on a convection versus diffusion (C/D) model, with the endodermis being the main barrier for solutes and water. Solute profiles in the stele were calculated as they occurred during rapid water flows across the root. The model quantitatively predicted the experimental finding of two distinct phases during PRs, in terms of a build-up of concentration profiles in the stele between endodermis and xylem vessels. It also predicted that, following a PC, half-times (T1/2) of PRs increased as the time used for clamping (and the build-up of USLs) increased. Following PCs of durations of 15, 30 and 60 s, T1/2 increased by factors of between 2.5 and 7.0, and water permeability of roots (root hydraulic conductivity, Lpr) was reduced by the same factors. When root pressure was immediately taken back to the original equilibrium root pressure following a PC, there was a transient uptake of water into the root stele (transient increase of root pressure), and the size of transients rose with time of clamping, as predicted by the model. The results indicated that the 'real' hydraulic conductivity of roots should be measured during initial water flows, such as during the rapid phase of PRs, when the effect of USLs was minimized. It was discussed that 'pressure-propagation effects' could not explain the finding of two phases during PRs. The results of USL effects threw some doubt on the use of PC and high-pressure flowmeter (HPFM) techniques with roots, where rigorous estimates of USLs were still missing despite the fact that large quantities of water were forced across the root.
Thorsten Knipfer; Debasish Das; Ernst Steudle
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Publication Detail:
Type:  Comparative Study; Journal Article    
Journal Detail:
Title:  Plant, cell & environment     Volume:  30     ISSN:  0140-7791     ISO Abbreviation:  Plant Cell Environ.     Publication Date:  2007 Jul 
Date Detail:
Created Date:  2007-06-05     Completed Date:  2007-09-21     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9309004     Medline TA:  Plant Cell Environ     Country:  United States    
Other Details:
Languages:  eng     Pagination:  845-60     Citation Subset:  IM    
Department of Plant Ecology, Bayreuth University, D-95440 Bayreuth, Germany.
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MeSH Terms
Biomechanics / instrumentation
Models, Biological
Plant Roots / physiology*
Time Factors
Zea mays / physiology*
Reg. No./Substance:

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