Glutamine synthetase: activity and localization in cyanobacteria of the cycadsCycas revoluta andZamia skinneri |
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Authors: | P Lindblad B Bergman |
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Institution: | (1) Institute of Physiological Botany, University of Uppsala, Box 540, S-75121 Uppsala, Sweden |
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Abstract: | Nitrogen-fixing cyanobacteria inhabit the zone between the inner and outer cortex of cycad coralloid roots. In the growing tip of such roots the cyanobacterial heterocyst frequency, nitrogenase activity (C2H2-reduction) and glutamine synthetase activity (both transferase and biosynthetic) were comparable to those found in freeliving cyanobacteria. The relative level of glutamine synthetase protein and its pattern of cellular/subcellular localization in heterocysts and vegetative cells were also similar to those of free-living cyanobacteria. However, there was a progressive decline in nitrogenase activity along the coralloid root with maximum reduction occurring in the regions farthest from the growing tip. A similar but less pronounced pattern was observed for glutamine synthetase activity. Distribution of glutamine synthetase protein in cyanobacteria in the first 2–3 mm of the root tip indicated a slight decrease in the heterocysts and vegetative cells. However, the overall level of cyanobacterial glutamine synthetase protein did not change because of a drastic increase in the numbers of heterocysts, which contain a proportionally higher level of glutamine synthetase than the vegetative cells.Abbreviation GS
glutamine synthetase |
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Keywords: | Cyanobacterium Cycad cyanobacterium symbiosis Cycas Glutamine synthetase Symbiosis Zamia |
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