Abstract
Glutamine synthetase (GS; EC 6.3.1.2) is a key enzyme of nitrogen assimilation, catalyzing the synthesis of glutamine from ammonium and glutamate. In Arabidopsis, cytosolic GS (GS1) was accumulated in roots when plants were excessively supplied with ammonium; however, the GS activity was controlled at a constant level. The discrepancy between the protein content and enzyme activity of GS1 was attributable to the kinetic properties and expression of four distinct isoenzymes encoded by GLN1;1, GLN1;2, GLN1;3 and GLN1;4, genes that function complementary to each other in Arabidopsis roots. GLN1;2 was the only isoenzyme significantly up-regulated by ammonium, which correlated with the rapid increase in total GS1 protein. GLN1;2 was localized in the vasculature and exhibited low affinities to ammonium (Km = 2450 +/- 150 microm) and glutamate (Km = 3.8 +/- 0.2 mm). The expression of the counterpart vascular tissue-localizing low affinity isoenzyme, GLN1;3, was not stimulated by ammonium; however, the enzyme activity of GLN1;3 was significantly inhibited by a high concentration of glutamate. By contrast, the high affinity isoenzyme, GLN1;1 (Km for ammonium < 10 microm; Km for glutamate = 1.1 +/- 0.4 mm) was abundantly accumulated in the surface layers of roots during nitrogen limitation and was down-regulated by ammonium excess. GLN1;4 was another high affinity-type GS1 expressed in nitrogen-starved plants but was 10-fold less abundant than GLN1;1. These results suggested that dynamic regulations of high and low affinity GS1 isoenzymes at the levels of mRNA and enzyme activities are dependent on nitrogen availabilities and may contribute to the homeostatic control of glutamine synthesis in Arabidopsis roots.
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Claims 17
Claim · model-written summary
Excess ammonium supply led to accumulation of cytosolic GS1 in Arabidopsis roots.
- Taxon
- Arabidopsis
Arabidopsist0 - Organ / stage
- rootse1
- Treatment
- excessively supplied with ammoniume1
- Gene
- GS1e1
- Outcome
- accumulatede1
- Direction
- increaseinferrede1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Arabidopsis”
e1“cytosolic GS (GS1) was accumulated in roots when plants were excessively supplied with ammonium”
Claim · model-written summary
Under excess ammonium supply, GS activity in Arabidopsis was controlled at a constant level.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- excessively supplied with ammoniume1
- Outcome
- GS activitye2
- Direction
- no_changeinferrede2
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Arabidopsis”
e1“cytosolic GS (GS1) was accumulated in roots when plants were excessively supplied with ammonium”
e2“however, the GS activity was controlled at a constant level”
Claim · model-written summary
The discrepancy between protein content and enzyme activity of GS1 in Arabidopsis is attributed to kinetic properties and expression of four isoenzymes.
- Taxon
- ArabidopsisArabidopsist0
- Outcome
- discrepancy between the protein content and enzyme activity of GS1e3
- Qualifier
- kinetic properties and expression of four distinct isoenzymese3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Arabidopsis”
e3“The discrepancy between the protein content and enzyme activity of GS1 was attributable to the kinetic properties and expression of four distinct isoenzymes”
Claim · model-written summary
GLN1;2 was the only isoenzyme significantly up-regulated by ammonium in Arabidopsis.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- ammoniume4
- Gene
- GLN1;2e4
- Outcome
- isoenzymee4
- Direction
- up-regulatede4
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Arabidopsis”
e4“GLN1;2 was the only isoenzyme significantly up-regulated by ammonium”
Claim · model-written summary
Up-regulation of GLN1;2 correlated with a rapid increase in total GS1 protein in Arabidopsis.
- Taxon
- ArabidopsisArabidopsist0
- Gene
- GLN1;2e4
- Outcome
- total GS1 proteine5
- Direction
- rapid increasee5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Arabidopsis”
e4“GLN1;2 was the only isoenzyme significantly up-regulated by ammonium”
e5“which correlated with the rapid increase in total GS1 protein”
Claim · model-written summary
GLN1;2 is localized in the vasculature of Arabidopsis roots.
- Taxon
- ArabidopsisArabidopsist0
- Organ / stage
- vasculaturee6
- Gene
- GLN1;2e6
- Outcome
- localized in the vasculaturee6
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Arabidopsis”
e6“GLN1;2 was localized in the vasculature”
Claim · model-written summary
GLN1;2 has a low affinity for ammonium in Arabidopsis, with Km of 2450 +/- 150 microM.
- Taxon
- ArabidopsisArabidopsist0
- Gene
- GLN1;2e6
- Compound
- ammoniume7
- Outcome
- low affinities to ammoniume7
- Value
- 2450 +/- 150 microme7
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Arabidopsis”
e6“GLN1;2 was localized in the vasculature”
e7“exhibited low affinities to ammonium (Km = 2450 +/- 150 microm)”
Claim · model-written summary
GLN1;2 has a low affinity for glutamate in Arabidopsis, with Km of 3.8 +/- 0.2 mM.
- Taxon
- ArabidopsisArabidopsist0
- Gene
- GLN1;2e6
- Compound
- glutamatee7
- Outcome
- low affinitiese7
- Value
- 3.8 +/- 0.2 mme7
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Arabidopsis”
e6“GLN1;2 was localized in the vasculature”
e7“exhibited low affinities to ammonium (Km = 2450 +/- 150 microm) and glutamate (Km = 3.8 +/- 0.2 mm)”
Claim · model-written summary
Expression of GLN1;3 in vascular tissue of Arabidopsis was not stimulated by ammonium.
- Taxon
- ArabidopsisArabidopsist0
- Organ / stage
- vascular tissuee1
- Treatment
- ammoniume1
- Gene
- GLN1;3e1
- Outcome
- expressione1
- Direction
- not stimulatede1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Arabidopsis”
e1“The expression of the counterpart vascular tissue-localizing low affinity isoenzyme, GLN1;3, was not stimulated by ammonium”
Claim · model-written summary
High glutamate concentration significantly inhibited GLN1;3 enzyme activity in Arabidopsis.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- a high concentration of glutamatee1
- Gene
- GLN1;3e1
- Outcome
- enzyme activitye1
- Direction
- inhibitede1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Arabidopsis”
e1“the enzyme activity of GLN1;3 was significantly inhibited by a high concentration of glutamate”
Claim · model-written summary
GLN1;1 in Arabidopsis has a Km for ammonium below 10 microM.
- Taxon
- ArabidopsisArabidopsist0
- Gene
- GLN1;1e1
- Compound
- ammoniume1
- Outcome
- Km for ammoniume1
- Value
- < 10 microme1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Arabidopsis”
e1“GLN1;1 (Km for ammonium < 10 microm; Km for glutamate = 1.1 +/- 0.4 mm)”
Claim · model-written summary
GLN1;1 in Arabidopsis has a Km for glutamate of 1.1 +/- 0.4 mM.
- Taxon
- ArabidopsisArabidopsist0
- Gene
- GLN1;1e1
- Compound
- glutamatee1
- Outcome
- Km for glutamatee1
- Value
- 1.1 +/- 0.4 mme1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Arabidopsis”
e1“GLN1;1 (Km for ammonium < 10 microm; Km for glutamate = 1.1 +/- 0.4 mm)”
Claim · model-written summary
GLN1;1 accumulated in the surface layers of Arabidopsis roots during nitrogen limitation.
- Taxon
- ArabidopsisArabidopsist0
- Organ / stage
- surface layers of rootse2
- Treatment
- nitrogen limitatione2
- Gene
- GLN1;1e1
- Outcome
- accumulatede2
- Direction
- increaseinferrede2
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Arabidopsis”
e1“GLN1;1 (Km for ammonium < 10 microm; Km for glutamate = 1.1 +/- 0.4 mm)”
e2“was abundantly accumulated in the surface layers of roots during nitrogen limitation”
Claim · model-written summary
Excess ammonium down-regulated GLN1;1 in Arabidopsis.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- ammonium excesse3
- Gene
- GLN1;1e1
- Outcome
- down-regulatede3
- Direction
- decreaseinferrede3
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Arabidopsis”
e1“GLN1;1 (Km for ammonium < 10 microm; Km for glutamate = 1.1 +/- 0.4 mm)”
e3“was down-regulated by ammonium excess”
Claim · model-written summary
GLN1;4 is expressed in nitrogen-starved Arabidopsis plants.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- nitrogen-starved plantse1
- Gene
- GLN1;4e1
- Outcome
- expressede1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Arabidopsis”
e1“GLN1;4 was another high affinity-type GS1 expressed in nitrogen-starved plants”
Claim · model-written summary
GLN1;4 is about 10-fold less abundant than GLN1;1 in Arabidopsis.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Arabidopsis”
e1“GLN1;4 was another high affinity-type GS1 expressed in nitrogen-starved plants”
e2“was 10-fold less abundant than GLN1;1”
Claim · model-written summary
Dynamic regulation of high and low affinity GS1 isoenzymes, dependent on nitrogen availability, may contribute to homeostatic control of glutamine synthesis in Arabidopsis roots.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- nitrogen availabilitiese1
- Gene
- high and low affinity GS1 isoenzymese1
- Outcome
- homeostatic control of glutamine synthesise1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Arabidopsis”
e1“These results suggested that dynamic regulations of high and low affinity GS1 isoenzymes at the levels of mRNA and enzyme activities are dependent on nitrogen availabilities and may contribute to the homeostatic control of glutamine synthesis in Arabidopsis roots”
The same questions in other papers
nitrogen · molecular: expression · ArabidopsisPositive and negative results
11 papers in the same direction as this paper · 6 in the opposite direction
- positive
- positive
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14 papers more in this group
See all 18 papers →nitrogen · physiology: gas exchange · ArabidopsisResults agree
1 paper in the same direction as this paper
- negative
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