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PLANTS INTERACTING WITH OTHER ORGANISMS

Adenylate-Coupled Ion Movement. A Mechanism for the Control of Nodule Permeability to O₂ Diffusion^1,[OA]

Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6

In response to changes in phloem supply, adenylate demand, and oxygen status, legume nodules are known to exercise rapid (seconds to hours) physiological control over their permeability to oxygen diffusion. Diffusion models have attributed this permeability control to the reversible flow of water into or out of intercellular spaces. To test hypotheses on the mechanism of diffusion barrier control, nodulated soybean (Glycine max L. Merr.) plants were exposed to a range of treatments known to alter nodule O₂ permeability (i.e. 10% O₂, 30% O₂, Ar:O₂ exposure, and stem girdling) before the nodules were rapidly frozen, freeze dried, and dissected into cortex and central zone (CZ) fractions that were assayed for K, Mg, and Ca ion concentrations. Treatments known to decrease nodule permeability (30% O₂, Ar:O₂ exposure, and stem girdling) were consistently associated with an increase in the ratio of [K⁺] in cortex to [K⁺] in the CZ tissue, whereas the 10% O₂ treatment, known to increase nodule permeability, was associated with a decrease in the [K⁺]_cortex:[K⁺]_CZ. When these findings were considered in the light of previous results, a proposed mechanism was developed for the adenylate-coupled movement of ions and water into and out of infected cells as a possible mechanism for diffusion barrier control in legume nodules.

² Present address: Section on Developmental Genetics, Heritable Disorders Branch, NICHD, National Institutes of Health, Bethesda, MA 20892–1830.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: David B. Layzell (layzelld{at}biology.queensu.ca).

^[OA] Open Access articles can be viewed online without a subscription.

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.106.077552.

^* Corresponding author; e-mail layzelld{at}biology.queensu.ca; fax 613–542–0045.

Received January 22, 2006; returned for revision January 22, 2006; accepted February 20, 2006.

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