ISSN:
1432-072X
Keywords:
Ammonium transport
;
Anabaena azollae
;
Anabaena variabilis
;
Cyanobacteria
;
Methylammonium transport
;
Symbiosis
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract The free-living cyanobacterium Anabaena variabilis showed a biphasic pattern of 14CH3NH 3 + uptake. Initial accumulation (up to 60 s) was independent of CH3NH 3 + metabolism, but long-term uptake was dependent on its metabolism via glutamine synthetase (GS). The CH3NH 3 + was converted into methylglutamine which was not further metabolised. The addition of l-methionine-dl-sulphoximine (MSX), to inhibit GS, inhibited CH3NH 3 + metabolism, but did not affect the CH3NH 3 + transport system. NH 4 + , when added after the addition of 14CH3NH 3 + , caused the efflux of free CH3NH 3 + ; when added before 14CH3NH 3 + , NH 4 + inhibited its uptake indicating that both NH 4 + and CH3NH 3 + share a common transport system. Carbonylcyanide m-chlorophenylhydrazone and triphenyl-methylphosphonium both inhibited CH3NH 3 + accumulation indicating that the transport system was Δψ-dependent. At pH 7 and at an external CH3NH 3 + concentration of 30 μmol dm-3, A. variabilis showed a 40-fold intracellular accumulation of CH3NH 3 + (internal concentration 1.4 mmol dm-3). Packets of the symbiotic cyanobacterium Anabaena azollae, directly isolated from the water fern Azolla caroliniana, also showed a Δψ-dependent NH 4 + transport system suggesting that the reduced inhibitory effect of NH 4 + on nitrogenase cannot be attributed to the absence of an NH 4 + transport system but is probably related to the reduced GS activity of the cyanobiont.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00414551
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