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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 root segments plotted against the internal oxygen concentration (Ci). According to Henry's law, 20.3, 38.7, 58.1, and 96.8% O2 (at a mean overpressures of 10 kPa) equated to 0.3, 0.57, 0.85, and 1.43 mol m−3 at the inner surface of the OPR, respectively. The radial O2 flows (JO2) increased with increasing O2 concentrations, but increases in JO2 were not linear, which was due to limitations of the technique (see Discussion). Red and blue dashed lines indicate the initial slopes (0% O2) of JO2/Ci curves for 30 mm and 60 mm, respectively. Data given are means ±SD (n=5–24 root segments).
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fig6: Rates of radial oxygen flow (JO2) along root segments plotted against the internal oxygen concentration (Ci). According to Henry's law, 20.3, 38.7, 58.1, and 96.8% O2 (at a mean overpressures of 10 kPa) equated to 0.3, 0.57, 0.85, and 1.43 mol m−3 at the inner surface of the OPR, respectively. The radial O2 flows (JO2) increased with increasing O2 concentrations, but increases in JO2 were not linear, which was due to limitations of the technique (see Discussion). Red and blue dashed lines indicate the initial slopes (0% O2) of JO2/Ci curves for 30 mm and 60 mm, respectively. Data given are means ±SD (n=5–24 root segments).

Mentions: Oxygen concentrations around the shoot were manipulated to test whether or not ROL increased with increasing oxygen concentration in the atmosphere as one would expect. Responses of ROL to different O2 concentrations around the shoot (20.3–96.8% O2/N2 mixtures, when considering the small effect due to humidification of the gases) at different distances from the root apex are shown in Fig. 3 (10, 30, and 60 mm). As the O2 concentration increased, rates of ROL significantly increased at all distances (F3,17=142.8 for 10 mm, F3,21=297.2 for 30 mm, F3,14=40.1 for 60 mm; P ≤0.05; Fig. 3A). However, in contrast to the perfusion experiments with root segments (see Figs. 5, 6), rates of O2 losses were much smaller (see Discussion). According to Fig. 3B, the increases of ROL were linear, but in all cases the regression lines did not pass through the origin. This may be explained by the fact that, at low O2 concentrations in the cortex, most of the oxygen is used by respiration. Extrapolating the regressions to intercept the x-axis provides concentration values when the use of oxygen in the plant just compensates axial diffusional transport along aerenchyma. The compensation points would be at 11, 7, and 14% for 10, 30, and 60 mm from the apex, respectively. The linear extrapolation may be questioned, and more data are required in the range of low concentrations (see Discussion). However, for all oxygen concentrations, there was a trend that the highest ROL was observed at 30 mm from the root tip, but this was only significant for 20.3% (F2,18=7.9; P ≤0.05; see Fig. 2 and 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 root segments plotted against the internal oxygen concentration (Ci). According to Henry's law, 20.3, 38.7, 58.1, and 96.8% O2 (at a mean overpressures of 10 kPa) equated to 0.3, 0.57, 0.85, and 1.43 mol m−3 at the inner surface of the OPR, respectively. The radial O2 flows (JO2) increased with increasing O2 concentrations, but increases in JO2 were not linear, which was due to limitations of the technique (see Discussion). Red and blue dashed lines indicate the initial slopes (0% O2) of JO2/Ci curves for 30 mm and 60 mm, respectively. Data given are means ±SD (n=5–24 root segments).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig6: Rates of radial oxygen flow (JO2) along root segments plotted against the internal oxygen concentration (Ci). According to Henry's law, 20.3, 38.7, 58.1, and 96.8% O2 (at a mean overpressures of 10 kPa) equated to 0.3, 0.57, 0.85, and 1.43 mol m−3 at the inner surface of the OPR, respectively. The radial O2 flows (JO2) increased with increasing O2 concentrations, but increases in JO2 were not linear, which was due to limitations of the technique (see Discussion). Red and blue dashed lines indicate the initial slopes (0% O2) of JO2/Ci curves for 30 mm and 60 mm, respectively. Data given are means ±SD (n=5–24 root segments).
Mentions: Oxygen concentrations around the shoot were manipulated to test whether or not ROL increased with increasing oxygen concentration in the atmosphere as one would expect. Responses of ROL to different O2 concentrations around the shoot (20.3–96.8% O2/N2 mixtures, when considering the small effect due to humidification of the gases) at different distances from the root apex are shown in Fig. 3 (10, 30, and 60 mm). As the O2 concentration increased, rates of ROL significantly increased at all distances (F3,17=142.8 for 10 mm, F3,21=297.2 for 30 mm, F3,14=40.1 for 60 mm; P ≤0.05; Fig. 3A). However, in contrast to the perfusion experiments with root segments (see Figs. 5, 6), rates of O2 losses were much smaller (see Discussion). According to Fig. 3B, the increases of ROL were linear, but in all cases the regression lines did not pass through the origin. This may be explained by the fact that, at low O2 concentrations in the cortex, most of the oxygen is used by respiration. Extrapolating the regressions to intercept the x-axis provides concentration values when the use of oxygen in the plant just compensates axial diffusional transport along aerenchyma. The compensation points would be at 11, 7, and 14% for 10, 30, and 60 mm from the apex, respectively. The linear extrapolation may be questioned, and more data are required in the range of low concentrations (see Discussion). However, for all oxygen concentrations, there was a trend that the highest ROL was observed at 30 mm from the root tip, but this was only significant for 20.3% (F2,18=7.9; P ≤0.05; see Fig. 2 and 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