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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) Development of oxidised methylene blue stains on the surface of the adventitious rice root. The rice root systems were placed for ∼20 h in 0.75% agar medium, which contained the redox indicator methylene blue in reduced form. The photographs was taken after removing roots from the agar medium. (B–D) Development of oxidised methylene blue haloes around the rice root segments. Root segments excised at a distance of 20–80 mm from the root apex were perfused with moistened air (20.3% O2) at an overpressure of 20 kPa for 0 (B), 15 (C), and 30 (D) min. Blue haloes were formed at the sites of oxygen loss from the segments. Black arrows indicate fixing points of the root segments to glass capillaries. Bar=10 mm.
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fig10: (A) Development of oxidised methylene blue stains on the surface of the adventitious rice root. The rice root systems were placed for ∼20 h in 0.75% agar medium, which contained the redox indicator methylene blue in reduced form. The photographs was taken after removing roots from the agar medium. (B–D) Development of oxidised methylene blue haloes around the rice root segments. Root segments excised at a distance of 20–80 mm from the root apex were perfused with moistened air (20.3% O2) at an overpressure of 20 kPa for 0 (B), 15 (C), and 30 (D) min. Blue haloes were formed at the sites of oxygen loss from the segments. Black arrows indicate fixing points of the root segments to glass capillaries. Bar=10 mm.

Mentions: Measurements of ROL with the root-sleeving platinum electrode provided a quantitative measure of oxygen loss from the roots. With the methylene blue agar technique, it was possible to visualize the pattern of ROL from roots by formation of the blue haloes at the sites where roots lost oxygen. For rice roots of intact plants placed in the growth chamber for 20 h, ROL occurred from the root apex up to distance of 60–100 mm. At larger distances, only blue patches on the surface of the roots were observed. The photograph in Fig. 10A was taken after removing roots from the agar medium (methylene blue was attached to the root surface at the sites of oxygen loss).


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) Development of oxidised methylene blue stains on the surface of the adventitious rice root. The rice root systems were placed for ∼20 h in 0.75% agar medium, which contained the redox indicator methylene blue in reduced form. The photographs was taken after removing roots from the agar medium. (B–D) Development of oxidised methylene blue haloes around the rice root segments. Root segments excised at a distance of 20–80 mm from the root apex were perfused with moistened air (20.3% O2) at an overpressure of 20 kPa for 0 (B), 15 (C), and 30 (D) min. Blue haloes were formed at the sites of oxygen loss from the segments. Black arrows indicate fixing points of the root segments to glass capillaries. Bar=10 mm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig10: (A) Development of oxidised methylene blue stains on the surface of the adventitious rice root. The rice root systems were placed for ∼20 h in 0.75% agar medium, which contained the redox indicator methylene blue in reduced form. The photographs was taken after removing roots from the agar medium. (B–D) Development of oxidised methylene blue haloes around the rice root segments. Root segments excised at a distance of 20–80 mm from the root apex were perfused with moistened air (20.3% O2) at an overpressure of 20 kPa for 0 (B), 15 (C), and 30 (D) min. Blue haloes were formed at the sites of oxygen loss from the segments. Black arrows indicate fixing points of the root segments to glass capillaries. Bar=10 mm.
Mentions: Measurements of ROL with the root-sleeving platinum electrode provided a quantitative measure of oxygen loss from the roots. With the methylene blue agar technique, it was possible to visualize the pattern of ROL from roots by formation of the blue haloes at the sites where roots lost oxygen. For rice roots of intact plants placed in the growth chamber for 20 h, ROL occurred from the root apex up to distance of 60–100 mm. At larger distances, only blue patches on the surface of the roots were observed. The photograph in Fig. 10A was taken after removing roots from the agar medium (methylene blue was attached to the root surface at the sites of oxygen loss).

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