Lipid composition and nitrogenase activity of symbioticFrankia (Alnus incana) in response to different oxygen concentrations |
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Authors: | Gisela Kleemann G Alskog Alison M Berry Kerstin Huss-Danell |
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Institution: | (1) Department of Plant Physiology, Umeå University, Umeå;(2) Department of Crop Science, Swedish University of Agricultural Sciences, Umeå;(3) Department of Environmental Horticulture, University of California, 95616 Davis, CA, USA |
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Abstract: | Summary The role ofFrankia vesicle envelope lipids in regulating oxygen diffusion of symbiotic nitrogen fixation inAlnus incana was examined. Total lipids of symbioticFrankia (vesicle clusters) that had been adapted to oxygen tensions of 5,21, or 40 kPa were analyzed with a normal phase HPLC system. During the oxygen treatment, nitrogenase activity was measured as hydrogen evolution in an open flow-through system. When plants were transferred to low oxygen (5 kPa) or high oxygen (40 kPa), nitrogenase activity dropped initially. Activity recovered in both treatments with a rate comparable to the controls (21 kPa O2). Both lipid content and lipid composition of vesicle clusters were affected by the oxygen treatments. With increasing oxygen tension, the vesicle cluster lipid content increased. This correlated with structural data (fluorescence microscopy and TEM) which showed a thicker vesicle envelope at higher oxygen tension. Three hopanoid lipids, bacteriohopanetetrol (bht) and two isomers of phenylacetyl monoester of bht, made up approximately 80% of the vesicle cluster lipids. With changing oxygen concentrations, the ratio of the two bht esters changed whereas the relative proportion of bht remained fairly constant. Therefore, in theFrankia-Alnus incana symbiosis, adaptation to different ambient oxygen tensions occurs at least partly by increasing the thickness of theFrankia vesicle envelope and by changing its lipid composition.Abbreviations dw
dry weight
- bht
bacteriohopanetetrol
- SE
standard error
- TEM
transmission electron microscopy
Dedicated to the memory of Professor John G. Torrey |
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Keywords: | Alnus incana Frankia Hopanoids Nitrogen fixation Oxygen Symbiosis Vesicle envelope |
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