Measurement of apoplasmic and cell-to-cell components of root hydraulic conductance by a pressure-clamp technique

Abstract

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 steadystate 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 x 10 -9 m 3. s -1' MPa -t, with values ranging from 12.0• 10 -9 to 18.5 x 10-9 m3.s-l-MPa-1; average cell-to-cell conductance was 11.7x 10 -9m3.s -~.MPa -~, with values ranging from 8.5 x 10 .9 to 15.3 x 10 -9 m3.s-l.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 2.7x10 -s to 5.6xl0-Sm's-l'MPa -t, with an average of 3.7 x 10 -8 m.s-l.MPa -~. The newly developed Abbreviations and symbols: A L 0 = root hydraulic conductance; AaL~ = root apoplasmic conductance; ACCL~, C = root cell-to-cell conductance; C~(t) = concentration of solutes in apical root compartment at time t; Jv = flow of water through the root; ja = apoplasmic flow of water; Jv ~c = cell-to-cell flow of water; LSC = leaf specific conductance of the root system; P = root hydrostatic pressure; P,ppt = applied pressure; n~(t) = root osmotic pressure at time t; rim, osmotic pressure of rooting medium; cr = reflection coefficient of root membrane; z = time constant of cell-to-cell flow decay Correspondence to: F. Magnani; Fax: 44 (31) 662 0478; Tel.: 44 (31) 650 5437; E-mail: fmagnani@srv0.bio.ed.ac.uk technique allows the interaction of mass flow of water and of solutes to be explored in the roots of soil-grown plants.

Competitive strategies for water availability in two Mediterranean Quercus species

“…the pressure chamber (Fiscus 1975; Rüdinger et al 1994), the root pressure probe (Steudle 1993) and the high pressure flow meter (HPFM, Tyree et al 1994, 1995). Although the most informative method is the root pressure probe, the HPFM is the only method developed so far (together with a similar instrumentation recently described by Magnani, Centritto & Grace 1996) that allows field measurements of K R in plants with trunks up to 60–80 mm in diameter.…”

Age‐related decline in stand productivity: the role of structural acclimation under hydraulic constraints

“…The hydraulic resistance of the root system is mainly determined by the radial resistance of fine roots ( Weatherley 1982; Magnani, Centritto & Grace 1996) and is therefore inversely related to the surface and, in first instance, to the biomass of feeder roots:…”

Water relations, photosynthesis, growth and water-use efficiency in tomato plants subjected to partial rootzone drying and regulated deficit irrigation

“…Both RDI and PRD can result in effective management strategies to increase water-use efficiency (WUE) in agriculture. Supplying water at a sub-optimal level generally results in the induction of a variety of water-deficit physiological responses that may lead to plant growth impairment (Kramer & Boyer, 1995;Magnani et al, 1996). Plant growth under water-deficit conditions can be limited as a result of decreased water status and, consequently, of impaired carbon assimilation (Lawlor & Cornic, 2002;Centritto et al, 2003;Chaves & Oliveira, 2004).…”