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

• Published in: Journal of experimental botany Vol. 60; no. 2; pp. 567 - 580
• Main Authors: Kotula, Lukasz, Steudle, Ernst
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 01.02.2009; Oxford Publishing Limited (England)
• Subjects: Aerenchyma; Biological and medical sciences; Coefficients; Diffusion - drug effects; Diffusion coefficient; Electric potential; Electrodes; Fundamental and applied biological sciences. Psychology; Methylene Blue; Oryza - drug effects; Oryza - metabolism; Oryza sativa; Overpressure; Oxidation-Reduction - drug effects; Oxygen; Oxygen - metabolism; Oxygen - pharmacology; oxygen permeability coefficient; Perfusion; Perfusion - methods; Permeability - drug effects; Plant roots; Plant Roots - drug effects; Plant Roots - metabolism; Plant Shoots - drug effects; Plant Shoots - metabolism; Plants; Polytetrafluoroethylene; radial oxygen loss; RESEARCH PAPER; Research Papers; Rice; rice root; Silicones; radial oxygen loss; Aerenchyma; rice root; oxygen permeability coefficient; Monocotyledones; Oxygen; Root; Permeability; Cereal crop; Oryza sativa; Gramineae; Angiospermae; Botany; Spermatophyta
• ISSN: 0022-0957; 1460-2431
• DOI: 10.1093/jxb/ern300

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 O2 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 O2 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)×10−6 m s−1 at 30 mm to (1.1±0.2)×10−6 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.