Interactions between cyanobacterium and fungus during 15N2-incorporation and metabolism in the lichen Peltigera canina |
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Authors: | Amar N Rai Peter Rowell William D P Stewart |
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Institution: | (1) A.R.C. Research Group on Cyanobacteria, University of Dundee, DD1 4HN Dundee, UK;(2) Department of Biological Sciences, University of Dundee, DD1 4HN Dundee, UK |
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Abstract: | On following N2-incorporation and subsequent metabolism in the lichen Peltigera canina using 15N as tracer, it was found, over a 30 min period, that greatest initial labelling was into NH
4
+
followed by glutamate and the amide-N of glutamine. Labelling of the amino-N of glutamine, aspartate and alanine increased slowly. Pulse-chase experiments using 15N confirmed this pattern. On inhibiting the GS-GOGAT pathway using l-methionine-dl-sulphoximine and azaserine, 15N enrichment of glutamate, alanine and aspartate continued although labelling of glutamine was undetectable. From this and enzymic data, NH
4
+
assimilation in the P. canina thallus appears to proceed via GS-GOGAT in the cyanobacterium and via GDH in the fungus; aminotransferases were present in both partners. The cyanobacterium assimilated 44% of the 15N2 fixed; the remainder was liberated almost exclusively as NH
4
+
and then assimilated by fungal GDH.Abbreviations ADH
alanine dehydrogenase
- APT
aspartate-pyruvate aminotransferase
- AOA
aminooxyacetate
- GDH
glutamate dehydrogenase
- GOT
glutamate-oxaloacetate aminotransferase
- GOGAT
glutamate synthase
- GPT
glutamate-pyruvate aminotransferase
- GS
glutamine synthetase
- HEPES
4-(2-hydroxyethyl)-1-piperazine ethanesulphonic acid
- MSX
l-methionine-dl-sulphoximine |
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Keywords: | Ammonia assimilation Lichen symbioses Nitrogen fixation 15N kinetics Peltigera canina |
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