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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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(A) Because of limitations of the technique in the range of high O2 concentrations (see Fig. 6), only the initial slopes (0–38.7% of O2) of JO2/Ci curves were used to calculate permeability coefficients of oxygen (PdO2). (B) The highest values of PdO2 were close to the root apex and decreased along the root, which is most probably due to suberization and/or lignification of roots. Data given are means ±SE (n=5).
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fig7: (A) Because of limitations of the technique in the range of high O2 concentrations (see Fig. 6), only the initial slopes (0–38.7% of O2) of JO2/Ci curves were used to calculate permeability coefficients of oxygen (PdO2). (B) The highest values of PdO2 were close to the root apex and decreased along the root, which is most probably due to suberization and/or lignification of roots. Data given are means ±SE (n=5).

Mentions: At all four distances, increases of JO2 with increasing concentration were not linear (Fig. 6). This may be caused by unstirred layers outside the root, where zero concentration of oxygen at the electrode was assumed (all O2 immediately reduced). Another reason may be an incomplete oxygen reduction, when two electrons are consumed per oxygen molecule rather than four, as described by Hahn et al. (1975; see Discussion). Because of the polarization effects at the platinum electrode at high JO2, only the initial slopes of the curves in Fig. 6 were used to calculate the oxygen permeability coefficient (Fig. 7A). The highest values of the oxygen permeability coefficient of the OPR (PdO2) along the rice root segments were at the positions closer to the root apex (30 mm) and decreased along the root, reaching the lowest value at 60 mm (Fig. 7B). PdO2 was significantly different between distances of 30 mm and 50 mm, and 40 mm and 60 mm (F3,16=11.1; P ≤0.05). The mean value of PdO2 at 60 mm was 0.9±0.1×10−6 m s−1, which was 2-fold smaller than that at 30 mm (1.9±0.07×10−6 m s−1).


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

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

(A) Because of limitations of the technique in the range of high O2 concentrations (see Fig. 6), only the initial slopes (0–38.7% of O2) of JO2/Ci curves were used to calculate permeability coefficients of oxygen (PdO2). (B) The highest values of PdO2 were close to the root apex and decreased along the root, which is most probably due to suberization and/or lignification of roots. Data given are means ±SE (n=5).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig7: (A) Because of limitations of the technique in the range of high O2 concentrations (see Fig. 6), only the initial slopes (0–38.7% of O2) of JO2/Ci curves were used to calculate permeability coefficients of oxygen (PdO2). (B) The highest values of PdO2 were close to the root apex and decreased along the root, which is most probably due to suberization and/or lignification of roots. Data given are means ±SE (n=5).
Mentions: At all four distances, increases of JO2 with increasing concentration were not linear (Fig. 6). This may be caused by unstirred layers outside the root, where zero concentration of oxygen at the electrode was assumed (all O2 immediately reduced). Another reason may be an incomplete oxygen reduction, when two electrons are consumed per oxygen molecule rather than four, as described by Hahn et al. (1975; see Discussion). Because of the polarization effects at the platinum electrode at high JO2, only the initial slopes of the curves in Fig. 6 were used to calculate the oxygen permeability coefficient (Fig. 7A). The highest values of the oxygen permeability coefficient of the OPR (PdO2) along the rice root segments were at the positions closer to the root apex (30 mm) and decreased along the root, reaching the lowest value at 60 mm (Fig. 7B). PdO2 was significantly different between distances of 30 mm and 50 mm, and 40 mm and 60 mm (F3,16=11.1; P ≤0.05). The mean value of PdO2 at 60 mm was 0.9±0.1×10−6 m s−1, which was 2-fold smaller than that at 30 mm (1.9±0.07×10−6 m s−1).

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