Modification of NO−3 metabolism in heterocysts of the N2-fixing cyanobacterium Anabaena 7120 (ATCC27893) |
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| Authors: | Amar N Rai Birgitta Bergman |
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| Institution: | Institute of Physiological Botany, Box 540, S-751 21 Uppsala, Sweden;Department of Biochemistry, North-Eastern Hill University, Shillong-793014, India |
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| Abstract: | Abstract The utilization of NO?3, NO?2 and NH+4 was studied in whole filaments and isolated heterocysts of Anabaena 7120 (ATCC27893). NO?3- and NO?2-uptake were detectable in whole filaments but not in heterocysts, whereas NH+4-uptake was detectable in both. Activity of NO?3-reductase was present in cell-free extracts of whole filaments but not of heterocysts, whereas activities of NO?2-reductase and glutamine synthetase were present in both. NO?3-uptake and reductase activities could not be induced in heterocysts even after prolonged incubation in NO?3 medium. It is suggested that NO?3-metabolism in heterocysts is impaired due to a selective and irreversible loss of NO?3-uptake and reductase systems resulting in the abolition of competition for molybdenum cofactor (Mo-Co) and reductant between nitrogenase and NO?3-reductase, and an increase in glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase levels. |
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| Keywords: | Anabaena sp heterocyst nitrate metabolism nitrogen fixation |
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