PMID- 17547656
OWN - NLM
STAT- MEDLINE
DCOM- 20070921
LR  - 20131121
IS  - 0140-7791 (Print)
IS  - 0140-7791 (Linking)
VI  - 30
IP  - 7
DP  - 2007 Jul
TI  - 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.
PG  - 845-60
AB  - 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.
FAU - Knipfer, Thorsten
AU  - Knipfer T
AD  - Department of Plant Ecology, Bayreuth University, D-95440 Bayreuth, Germany.
FAU - Das, Debasish
AU  - Das D
FAU - Steudle, Ernst
AU  - Steudle E
LA  - eng
PT  - Comparative Study
PT  - Journal Article
PL  - United States
TA  - Plant Cell Environ
JT  - Plant, cell & environment
JID - 9309004
RN  - 059QF0KO0R (Water)
SB  - IM
MH  - Biomechanical Phenomena/instrumentation
MH  - Flowmeters
MH  - Models, Biological
MH  - Plant Roots/*physiology
MH  - *Pressure
MH  - Time Factors
MH  - *Water
MH  - Zea mays/*physiology
EDAT- 2007/06/06 09:00
MHDA- 2007/09/22 09:00
CRDT- 2007/06/06 09:00
PHST- 2007/06/06 09:00 [pubmed]
PHST- 2007/09/22 09:00 [medline]
PHST- 2007/06/06 09:00 [entrez]
AID - PCE1670 [pii]
AID - 10.1111/j.1365-3040.2007.01670.x [doi]
PST - ppublish
SO  - Plant Cell Environ. 2007 Jul;30(7):845-60. doi: 10.1111/j.1365-3040.2007.01670.x.