Lateral hydraulic conductivity of early metaxylem vessels in Zea mays L. roots |
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Authors: | Carol A Peterson Ernst Steudle |
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Institution: | (1) Department of Biology, University of Waterloo, N2L 3G1 Waterloo, ON, Canada;(2) Lehrstuhl für Pflanzenökologie, Universität Bayreuth, Universitätsstrasse 30, W-8580 Bayreuth, FRG |
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Abstract: | The hydraulic conductivity of the lateral walls of early metaxylem vessels (Lpx in m · s–1 · MPa–1) was measured in young, excised roots of maize using a root pressure probe. Values for this parameter were determined by comparing the root hydraulic conductivities before and after steam-ringing a short zone on each root. Killing of living tissue virtually canceled its hydraulic resistance. There were no suberin lamellae present in the endodermis of the roots used. The value of Lpx ranged between 3 · 10–7 and 35 · 10–7 m · s–1 · MPa–1 and was larger than the hydraulic conductivity of the untreated root (Lpr = 0.7 · 10–7 to 4.0 · 10–7 m · s–1 · MPa–1) by factor of 3 to 13. Assuming that all flow through the vessel walls was through the pit membranes, which occupied 14% of the total wall area, an upper limit of the hydraulic conductivity of this structure could be given(Lppm=21 · 10–7 to 250 · 10–7 m · s–1 · MPa–1). The specific hydraulic conductivity (Lpcw) of the wall material of the pit membranes (again an upper limit) ranged from 0.3 · 10–12 to 3.8 · 10–12 m2 · s–1 · MPa–1 and was lower than estimates given in the literature for plant cell walls. From the data, we conclude that the majority of the radial resistance to water movement in the root is contributed by living tissue. However, although the lateral walls of the vessels do not limit the rate of water flow in the intact system, they constitute 8–31% of the total resistance, a value which should not be ignored in a detailed analysis of water flow through roots.Abbreviatations and Symbols kwr (T
1
2/W
)
rate constant (half-time) of water exchange across root (s–1 or s, respectively)
- Lpcw
specific hydraulic conductivity of wall material (m2 · s–1 · MPa–1)
- Lppm
hydraulic conductivity of pit membranes (m · s –1 · MPa–1)
- Lpr
hydraulic conductivity of root (m · s–1 · MPa–1)
- Lpx
lateralhydraulic conductivity of walls of root xylem (m · s –1 · MPa–1)
This research was supported by a grant from the Bilateral Exchange Program funded jointly by the Natural Sciences and Engineering Research Council of Canada and the Deutsche Forschungsgemeinschaft to C.A.P., and by a grant from the Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 137, to E.S. The expert technical help of Mr. Burkhard Stumpf and the work of Ms. Martina Murrmann and Ms. Hilde Zimmermann in digitizing chart-recorder strips is gratefully acknowledged. |
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Keywords: | Hydraulic conductivity Pit (membrane hydraulic conductivity) Root Xylem Zea |
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