JXB Advance Access published online on December 16, 2008
Journal of Experimental Botany, doi:10.1093/jxb/ern300
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© 2009 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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RESEARCH PAPER |
Measurements of oxygen permeability coefficients of rice (Oryza sativa L.) roots using a new perfusion technique
Department of Plant Ecology, University of Bayreuth, D-95440 Bayreuth, Germany
* To whom correspondence should be addressed. E-mail: ernst.steudle{at}uni-bayreuth.de
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)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.
Key words: Aerenchyma, oxygen permeability coefficient, Oryza sativa, radial oxygen loss, rice root
Received 28 July 2008; Revised 30 October 2008 Accepted 31 October 2008
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  L. Kotula, K. Ranathunge, L. Schreiber, and E. Steudle Functional and chemical comparison of apoplastic barriers to radial oxygen loss in roots of rice (Oryza sativa L.) grown in aerated or deoxygenated solution J. Exp. Bot., May 1, 2009; 60(7): 2155 - 2167. [Abstract] [Full Text] [PDF]
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