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Measurements of oxygen permeability coefficients of rice (Oryza sativa L.) roots using a new perfusion technique.

Kotula L, Steudle E - J. Exp. Bot. (2008)

Bottom Line: They decreased from (2.8+/-0.2)x10(-6) m s(-1) at 30 mm to (1.1+/-0.2)x10(-6) m s(-1) at 60 mm from the apex (n=5; +/-SE).Low diffusional oxygen permeability of the OPR suggested that the barrier to radial oxygen loss was effective.The results are discussed in terms of the inter-relationship between the water and oxygen permeabilities as roots develop in either aerated or deoxygenated (stagnant) media.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Ecology, University of Bayreuth, D-95440 Bayreuth, Germany.

ABSTRACT
A new approach is described to analyse the barrier properties of the outer part of rice (Oryza sativa L.) roots towards oxygen. By using a root-sleeving O(2) electrode, radial oxygen loss at different distances from the root apex was measured and related to the corresponding root structure. In addition, internal oxygen concentrations were precisely adjusted using a newly developed perfusion technique. Thus, the oxygen permeability coefficient of the outer part of the root (OPR) could be calculated, since both (i) the oxygen flow across the OPR and (ii) the oxygen concentration gradient across the OPR from inside to outside were known. On the basis of the permeability coefficient, it can be decided whether or not different rates of oxygen loss across the OPR are due to changes in the OPR structure and/or to changes in the concentration gradient. The technique was applied to rice root segments, which enabled rapid perfusion of aerenchyma. In the present study, roots of rice grown under aerobic conditions were used which should have a higher O(2) permeability compared with that of plants grown in deoxygenated solution. Both radial oxygen losses and permeability coefficients decreased along the root, reaching the lowest values at the basal positions. Values of oxygen permeability coefficients of the OPR were corrected for external unstirred layers. They decreased from (2.8+/-0.2)x10(-6) m s(-1) at 30 mm to (1.1+/-0.2)x10(-6) m s(-1) at 60 mm from the apex (n=5; +/-SE). They were similar to those measured previously for cuticles. Low diffusional oxygen permeability of the OPR suggested that the barrier to radial oxygen loss was effective. This may help to retain oxygen within the root and enhance diffusion of oxygen towards the apex in the presence of a relatively high water permeability. The results are discussed in terms of the inter-relationship between the water and oxygen permeabilities as roots develop in either aerated or deoxygenated (stagnant) media.

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Rates of radial oxygen flow (JO2) along the root when perfused with 20.3% O2 at overpressures of 10, 20, and 30 kPa at the entrance of the segments (reference atmospheric pressure 100 kPa=0.1 MPa). Assuming a linear drop in pressure along the segments for the three different pressures, average values of 105, 110, and 115 kPa were used to calculate PO2 and the actual O2 concentration. For each distance from the root apex, radial oxygen flows increased with increasing overpressures, but increases were not significantly different. Measurements were taken at 25 °C in a temperature-controlled room. Data given are means ±SE (n=8).
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fig4: Rates of radial oxygen flow (JO2) along the root when perfused with 20.3% O2 at overpressures of 10, 20, and 30 kPa at the entrance of the segments (reference atmospheric pressure 100 kPa=0.1 MPa). Assuming a linear drop in pressure along the segments for the three different pressures, average values of 105, 110, and 115 kPa were used to calculate PO2 and the actual O2 concentration. For each distance from the root apex, radial oxygen flows increased with increasing overpressures, but increases were not significantly different. Measurements were taken at 25 °C in a temperature-controlled room. Data given are means ±SE (n=8).

Mentions: Perfusion of aerenchyma with different oxygen concentrations and different overpressures (axial flow rates) was performed with rice root segments placed in O2-free medium, and radial oxygen flows (JO2s) were measured. When root segments were perfused with humidified air (20.3% O2) at overpressures of 10, 20, or 30 kPa at the entrance of segments (Teflon tubes), there was a slight increase in JO2, but this was not significant (F2,21=1.1, 0.2, 0.2, and 0.3 for 30, 40, 50, and 60 mm, respectively; P>0.05; Fig. 4). It was also not significant when data were not pooled (as in the figure) but were plotted root-by-root (data not shown). Different overpressures were used to check whether the axial perfusion of aerenchyma with oxygen was rapid enough to provide a constant internal O2 concentration along the root interior and to compensate for losses of oxygen by respiration (see Discussion). According to gas laws, higher absolute pressures at the inlet (110, 120, and 130 kPa) would increase the partial oxygen pressure (PO2) and the actual concentration of oxygen along the tubes (segments). Assuming that the drop in pressure would be largely within the segments and would be linear for the three different pressures, average values of 105, 110, and 115 kPa were used to calculate PO2 and the actual O2 concentration (see Discussion). As seen in Fig. 4, there was a drop of JO2 along the root from 30 mm to 60 mm (see Fig. 5). It was not possible to make measurements at distances below 30 mm (see Discussion). For the rest of the experiments, an overpressure of 20 kPa (0.02 MPa) was used at the entrance of the segments, which was sufficient to keep the constant O2 concentration in the aerenchyma (see Discussion).


Measurements of oxygen permeability coefficients of rice (Oryza sativa L.) roots using a new perfusion technique.

Kotula L, Steudle E - J. Exp. Bot. (2008)

Rates of radial oxygen flow (JO2) along the root when perfused with 20.3% O2 at overpressures of 10, 20, and 30 kPa at the entrance of the segments (reference atmospheric pressure 100 kPa=0.1 MPa). Assuming a linear drop in pressure along the segments for the three different pressures, average values of 105, 110, and 115 kPa were used to calculate PO2 and the actual O2 concentration. For each distance from the root apex, radial oxygen flows increased with increasing overpressures, but increases were not significantly different. Measurements were taken at 25 °C in a temperature-controlled room. Data given are means ±SE (n=8).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2651460&req=5

fig4: Rates of radial oxygen flow (JO2) along the root when perfused with 20.3% O2 at overpressures of 10, 20, and 30 kPa at the entrance of the segments (reference atmospheric pressure 100 kPa=0.1 MPa). Assuming a linear drop in pressure along the segments for the three different pressures, average values of 105, 110, and 115 kPa were used to calculate PO2 and the actual O2 concentration. For each distance from the root apex, radial oxygen flows increased with increasing overpressures, but increases were not significantly different. Measurements were taken at 25 °C in a temperature-controlled room. Data given are means ±SE (n=8).
Mentions: Perfusion of aerenchyma with different oxygen concentrations and different overpressures (axial flow rates) was performed with rice root segments placed in O2-free medium, and radial oxygen flows (JO2s) were measured. When root segments were perfused with humidified air (20.3% O2) at overpressures of 10, 20, or 30 kPa at the entrance of segments (Teflon tubes), there was a slight increase in JO2, but this was not significant (F2,21=1.1, 0.2, 0.2, and 0.3 for 30, 40, 50, and 60 mm, respectively; P>0.05; Fig. 4). It was also not significant when data were not pooled (as in the figure) but were plotted root-by-root (data not shown). Different overpressures were used to check whether the axial perfusion of aerenchyma with oxygen was rapid enough to provide a constant internal O2 concentration along the root interior and to compensate for losses of oxygen by respiration (see Discussion). According to gas laws, higher absolute pressures at the inlet (110, 120, and 130 kPa) would increase the partial oxygen pressure (PO2) and the actual concentration of oxygen along the tubes (segments). Assuming that the drop in pressure would be largely within the segments and would be linear for the three different pressures, average values of 105, 110, and 115 kPa were used to calculate PO2 and the actual O2 concentration (see Discussion). As seen in Fig. 4, there was a drop of JO2 along the root from 30 mm to 60 mm (see Fig. 5). It was not possible to make measurements at distances below 30 mm (see Discussion). For the rest of the experiments, an overpressure of 20 kPa (0.02 MPa) was used at the entrance of the segments, which was sufficient to keep the constant O2 concentration in the aerenchyma (see Discussion).

Bottom Line: They decreased from (2.8+/-0.2)x10(-6) m s(-1) at 30 mm to (1.1+/-0.2)x10(-6) m s(-1) at 60 mm from the apex (n=5; +/-SE).Low diffusional oxygen permeability of the OPR suggested that the barrier to radial oxygen loss was effective.The results are discussed in terms of the inter-relationship between the water and oxygen permeabilities as roots develop in either aerated or deoxygenated (stagnant) media.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Ecology, University of Bayreuth, D-95440 Bayreuth, Germany.

ABSTRACT
A new approach is described to analyse the barrier properties of the outer part of rice (Oryza sativa L.) roots towards oxygen. By using a root-sleeving O(2) electrode, radial oxygen loss at different distances from the root apex was measured and related to the corresponding root structure. In addition, internal oxygen concentrations were precisely adjusted using a newly developed perfusion technique. Thus, the oxygen permeability coefficient of the outer part of the root (OPR) could be calculated, since both (i) the oxygen flow across the OPR and (ii) the oxygen concentration gradient across the OPR from inside to outside were known. On the basis of the permeability coefficient, it can be decided whether or not different rates of oxygen loss across the OPR are due to changes in the OPR structure and/or to changes in the concentration gradient. The technique was applied to rice root segments, which enabled rapid perfusion of aerenchyma. In the present study, roots of rice grown under aerobic conditions were used which should have a higher O(2) permeability compared with that of plants grown in deoxygenated solution. Both radial oxygen losses and permeability coefficients decreased along the root, reaching the lowest values at the basal positions. Values of oxygen permeability coefficients of the OPR were corrected for external unstirred layers. They decreased from (2.8+/-0.2)x10(-6) m s(-1) at 30 mm to (1.1+/-0.2)x10(-6) m s(-1) at 60 mm from the apex (n=5; +/-SE). They were similar to those measured previously for cuticles. Low diffusional oxygen permeability of the OPR suggested that the barrier to radial oxygen loss was effective. This may help to retain oxygen within the root and enhance diffusion of oxygen towards the apex in the presence of a relatively high water permeability. The results are discussed in terms of the inter-relationship between the water and oxygen permeabilities as roots develop in either aerated or deoxygenated (stagnant) media.

Show MeSH
Related in: MedlinePlus