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Nitrogen Starvation Acclimation in Synechococcus elongatus: Redox-Control and the Role of Nitrate Reduction as an Electron Sink.

Klotz A, Reinhold E, Doello S, Forchhammer K - Life (Basel) (2015)

Bottom Line: This study established a method that allows uncoupling metabolic and redox-signals involved in nitrogen-starvation acclimation.This study demonstrates that nitrogen starvation is perceived not only through metabolic signals, but requires a redox signal indicating over-reduction of PSI-reduced electron acceptors.It further establishes a cryptic role of nitrate/nitrite reductases as electron sinks to balance conditions of over-reduction.

View Article: PubMed Central - PubMed

Affiliation: Interfakultäres Institut für Mikrobiologie und Infektionsmedizin der Eberhard-Karls-Universität Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany. alexander.klotz@uni-tuebingen.de.

ABSTRACT
Nitrogen starvation acclimation in non-diazotrophic cyanobacteria is characterized by a process termed chlorosis, where the light harvesting pigments are degraded and the cells gradually tune down photosynthetic and metabolic activities. The chlorosis response is governed by a complex and poorly understood regulatory network, which converges at the expression of the nblA gene, the triggering factor for phycobiliprotein degradation. This study established a method that allows uncoupling metabolic and redox-signals involved in nitrogen-starvation acclimation. Inhibition of glutamine synthetase (GS) by a precise dosage of l-methionine-sulfoximine (MSX) mimics the metabolic situation of nitrogen starvation. Addition of nitrate to such MSX-inhibited cells eliminates the associated redox-stress by enabling electron flow towards nitrate/nitrite reduction and thereby, prevents the induction of nblA expression and the associated chlorosis response. This study demonstrates that nitrogen starvation is perceived not only through metabolic signals, but requires a redox signal indicating over-reduction of PSI-reduced electron acceptors. It further establishes a cryptic role of nitrate/nitrite reductases as electron sinks to balance conditions of over-reduction.

No MeSH data available.


Related in: MedlinePlus

Determination of intracellular glycogen content in WT-C 103 cells incubated in BG0 with nitrate or ammonia with or without 2 µM MSX within 24 h.
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life-05-00888-f010: Determination of intracellular glycogen content in WT-C 103 cells incubated in BG0 with nitrate or ammonia with or without 2 µM MSX within 24 h.

Mentions: Finally, we checked whether MSX may differentially interfere with glycogen synthesis in the presence of ammonium or nitrate, and thereby could affect nblA induction. Therefore, we measured the accumulation of glycogen in the presence of nitrate or ammonia, with or without addition of 2 µM MSX. As shown in Figure 10, glycogen accumulated upon MSX treatment and there was no significant difference in glycogen accumulation between nitrate and ammonium conditions after 5 and 24 h of MSX treatment. In the presence of ammonia, the glycogen maximum was already reached after 10 h, whereas the glycogen level in the presence of nitrate at 10 h was slightly lower, which might be accounted for the consumption of reducing equivalents by nitrate and nitrite reductase.


Nitrogen Starvation Acclimation in Synechococcus elongatus: Redox-Control and the Role of Nitrate Reduction as an Electron Sink.

Klotz A, Reinhold E, Doello S, Forchhammer K - Life (Basel) (2015)

Determination of intracellular glycogen content in WT-C 103 cells incubated in BG0 with nitrate or ammonia with or without 2 µM MSX within 24 h.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4390884&req=5

life-05-00888-f010: Determination of intracellular glycogen content in WT-C 103 cells incubated in BG0 with nitrate or ammonia with or without 2 µM MSX within 24 h.
Mentions: Finally, we checked whether MSX may differentially interfere with glycogen synthesis in the presence of ammonium or nitrate, and thereby could affect nblA induction. Therefore, we measured the accumulation of glycogen in the presence of nitrate or ammonia, with or without addition of 2 µM MSX. As shown in Figure 10, glycogen accumulated upon MSX treatment and there was no significant difference in glycogen accumulation between nitrate and ammonium conditions after 5 and 24 h of MSX treatment. In the presence of ammonia, the glycogen maximum was already reached after 10 h, whereas the glycogen level in the presence of nitrate at 10 h was slightly lower, which might be accounted for the consumption of reducing equivalents by nitrate and nitrite reductase.

Bottom Line: This study established a method that allows uncoupling metabolic and redox-signals involved in nitrogen-starvation acclimation.This study demonstrates that nitrogen starvation is perceived not only through metabolic signals, but requires a redox signal indicating over-reduction of PSI-reduced electron acceptors.It further establishes a cryptic role of nitrate/nitrite reductases as electron sinks to balance conditions of over-reduction.

View Article: PubMed Central - PubMed

Affiliation: Interfakultäres Institut für Mikrobiologie und Infektionsmedizin der Eberhard-Karls-Universität Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany. alexander.klotz@uni-tuebingen.de.

ABSTRACT
Nitrogen starvation acclimation in non-diazotrophic cyanobacteria is characterized by a process termed chlorosis, where the light harvesting pigments are degraded and the cells gradually tune down photosynthetic and metabolic activities. The chlorosis response is governed by a complex and poorly understood regulatory network, which converges at the expression of the nblA gene, the triggering factor for phycobiliprotein degradation. This study established a method that allows uncoupling metabolic and redox-signals involved in nitrogen-starvation acclimation. Inhibition of glutamine synthetase (GS) by a precise dosage of l-methionine-sulfoximine (MSX) mimics the metabolic situation of nitrogen starvation. Addition of nitrate to such MSX-inhibited cells eliminates the associated redox-stress by enabling electron flow towards nitrate/nitrite reduction and thereby, prevents the induction of nblA expression and the associated chlorosis response. This study demonstrates that nitrogen starvation is perceived not only through metabolic signals, but requires a redox signal indicating over-reduction of PSI-reduced electron acceptors. It further establishes a cryptic role of nitrate/nitrite reductases as electron sinks to balance conditions of over-reduction.

No MeSH data available.


Related in: MedlinePlus