Effects of anaerobic conditions on water and solute relations,and on active transport in roots of maize (Zea mays L.) |
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Authors: | Thomas P Birner Ernst Steudle |
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Institution: | (1) Lehrstuhl Pflanzenökologie, Universität Bayreuth, Universitätstraße 30, W-8580 Bayreuth, FRG |
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Abstract: | The effects of anoxia on water and solute transport across excised roots of young maize plants (Zea mays L. cv. Tanker) grown hydroponically have been studied. With the aid of the root pressure probe, root pressure (Pr), root hydraulic conductivity (Lpr), and root permeability (Psr), and reflection (
sr) coefficients were measured using potassium nitrate (a typical nutrient salt) and sodium nitrate (an atypical nutrient salt) as solutes. During a period of 10–15 h, anaerobic treatment (0.0–0.2 g O2·m-3 in root medium) caused a decrease of root pressure by 0.01–0.28 MPa (by 10–80% of original root pressure) after a short transient increase. For a time period of 5 h, the decrease in the stationary root pressure was not reversible. Under anaerobic conditions, roots still behaved like osmometers and were not leaky. The root hydraulic conductivity measured in osmotic experiments (osmotic solute: NaNO3) was smaller by one to two orders of magnitude than that measured in the presence of hydrostatic gradients. Both the osmotic and hydrostatic hydraulic conductivity decreased during anaerobic treatment by 28 and 44%, respectively, at a constant reflection coefficient of the solutes (
sr=0.3–1.0). As with root pressure, changes in root permeability to water and solutes were not reversible within 5 h. Under aerobic conditions and at low external concentrations (31–59 mOsmol·kg-1), osmotic response curves were monophasic for KNO3, i.e. there was no passive uptake of solutes. Response curves became biphasic at higher concentrations (100–150 mOsmol·kg-1)- For NaNO3, response curves were biphasic at all concentrations. Presumably, this pattern was a consequence of the fact that potassium had already accumulated in the xylem. During anoxia, accumulation of potassium in the xylem was reduced, and biphasic responses were also obtained at lower potassium concentrations applied to the medium. The results are discussed in terms of a pump/leak model of the root in which anoxia affects both the active ion pumping and the permeability of the root to nutrient salts (leakage). The effects of anaerobiosis on the passive transport properties of the root (Lpr, Psr,
sr) are in line with the recently proposed composite transport model of the root.Abbreviations and Symbols Ar
root surface area
- Lpr
root hydraulic conductivity
- Lprh
hydrostatic hydraulic conductivity of root
- Lpro
osmotic hydraulic conductivity of root
- Pr
root pressure
- Psr
permeability coefficient of root
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sr
reflection coefficient of root
The authors thank Mr. Walter Melchior for the curve-fitting program used to work out Lprh values from root pressure relaxations and Mr. Mohammad Hajirezai (Lehrstuhl für Pflanzenphysiologie, Universität Bayreuth) for making the ATP measurements. The assistance of Mrs. Libuse Badewitz in making the drawings and the technical help of Mr. Burkhard Stumpf are also gratefully acknowledged. |
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Keywords: | Anaerobiosis Hydraulic conductivity Reflection coefficient Root pressure probe Permeability coefficient Zea (root water) |
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