Measurement of apoplasmic and cell-to-cell components of root hydraulic conductance by a pressure-clamp technique |
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Authors: | Federico Magnani Mauro Centritto John Grace |
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Institution: | (1) Institute of Ecology and Resource Management, University of Edinburgh, Darwin Building, King's Buildings, Mayfield Road, EH9 3JU Edinburgh, UK;(2) Istituto Irrigazione, Consiglio Nazionale delle Ricerche, via Cupa Patacca 85, I-80056 Ercolano (NA), Italy |
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Abstract: | A pressure-clamp technique was devised for the direct measurement of cell-to-cell and apoplasmic components of root hydraulic conductance; the experimental results were analyzed in terms of a theoretical model of water and solute flow, based on a composite membrane model of the root. When water is forced under a constant pressure into a cut root system, an exponential decay of flow is observed, until a constant value is attained; when pressure is released, a reverse water flow out of the root system is observed which shows a similar exponential behavour. The model assumes that the transient flow occurs through a cell-to-cell pathway and the observed decrease is the result of accumulation of solutes in front of the root semi-permeable membrane, whilst the steady-state component results from the movement of water through the parallel apoplasmic pathway. Root conductance components are estimated by fitting the model to experimental data. The technique was applied to the root systems of potted cherry (Prunus avium L.) seedlings; average apoplasmic conductance was 15.5 × 10–9m3· s–1· MPa–1, with values ranging from 12.0 × 10–9 to 18.5 × 10–9m3· s–1· MPa–1; average cell-to-cell conductance was 11.7 × 109 m3· s–1· MPa–1, with values ranging from 8.5 × 10–9 to 15.3 × 10–9 m3 · s–1·MPa–1. Cell-to-cell conductance amounted on average to 43% of total root conductance, with values between 41 and 45%. Leaf specific conductance (conductance per unit of leaf area supported) of the root systems ranged from 2.7 × 10–8 to 5.6 × 10–8 m· s–1·MPa–1, with an average of 3.7 × 10–8 m · s–1·MPa–1. The newly developed technique allows the interaction of mass flow of water and of solutes to be explored in the roots of soil-grown plants.Abbreviations and Symbols A Lp
root hydraulic conductance
- AaL
p
a
root apoplasmic conductance
- AccL
p
cc
root cell-to-cell conductance
- Cs(t)
concentration of solutes in apical root compartment at time t
- Jv
flow of water through the root
- J
v
a
apoplasmic flow of water
- Jv/cc
cell-to-cell flow of water
- LSC
leaf specific conductance of the root system
- P
root hydrostatic pressure
- Pappl
applied pressure
- s(t)
root osmotic pressure at time t
- m
osmotic pressure of rooting medium
-
reflection coefficient of root membrane
-
time constant of cell-to-cell flow decay
This research was funded within the EC Project Long-term effects of CO2-increase and climate change on European forests (LTEEF) (EV5V-CT94-0468); F.M. was supported by a Ministero dell' Universitá e della Ricerca Scientifica e Tecnologica — British Council agreement (Project The ecological significance of cavitation in woody plants ); M.C. was supported by a Consiglio Nazionale delle Ricerche — British Council agreement. We gratefully thank Prof. P.G. Jarvis (University of Edinburgh, UK) for revising an earlier version of this paper and Prof. E. Steudle (University of Bayreuth, Germany) for helpful comments. |
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Keywords: | Apoplasm Hydraulic conductance Pressure clamp technique Prunus (water relations) Root (hydraulic conductance) Water relations |
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