Abstract
The role of potassium (K(+)) transporters in high- and low-affinity K(+) uptake was examined in roots of intact barley (Hordeum vulgare) and Arabidopsis (Arabidopsis thaliana) plants by use of (42)K radiotracing, electrophysiology, pharmacology, and mutant analysis. Comparisons were made between results from barley and five genotypes of Arabidopsis, including single and double knockout mutants for the high-affinity transporter, AtHAK5, and the Shaker-type channel, AtAKT1. In Arabidopsis, steady-state K(+) influx at low external K(+) concentration ([K(+)]ext = 22.5 µm) was predominantly mediated by AtAKT1 when high-affinity transport was inhibited by ammonium, whereas in barley, by contrast, K(+) channels could not operate below 100 µm. Withdrawal of ammonium resulted in an immediate and dramatic stimulation of K(+) influx in barley, indicating a shift from active to passive K(+) uptake at low [K(+)]ext and yielding fluxes as high as 36 µmol g (root fresh weight)(-1) h(-1) at 5 mm [K(+)]ext, among the highest transporter-mediated K(+) fluxes hitherto reported. This ammonium-withdrawal effect was also established in all Arabidopsis lines (the wild types, atakt1, athak5, and athak5 atakt1) at low [K(+)]ext, revealing the concerted involvement of several transport systems. The ammonium-withdrawal effect coincided with a suppression of K(+) efflux and a significant hyperpolarization of the plasma membrane in all genotypes except athak5 atakt1, could be sustained over 24 h, and resulted in increased tissue K(+) accumulation. We discuss key differences and similarities in K(+) acquisition between two important model systems and reveal novel aspects of K(+) transport in planta.
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Claims 9
Claim · model-written summary
In Arabidopsis at low external K(+), steady-state K(+) influx was mainly mediated by AtAKT1 when ammonium inhibited high-affinity transport
- Taxon
- Arabidopsis
Arabidopsise1 - Treatment
- high-affinity transport was inhibited by ammoniume1
- Gene
- AtAKT1e1
- Outcome
- steady-state K(+) influxe1
- Qualifier
- low external K(+) concentration ([K(+)]ext = 22.5 µm)e1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Roots of Barley and Arabidopsis”
e1“In Arabidopsis, steady-state K(+) influx at low external K(+) concentration ([K(+)]ext = 22.5 µm) was predominantly mediated by AtAKT1 when high-affinity transport was inhibited by ammonium, whereas in barley, by contrast, K(+) channels could not operate below 100 µm”
Claim · model-written summary
In barley, K(+) channels could not operate below 100 µm external K(+)
- Taxon
- barley
.jpg?width=60)
Hordeum vulgaree1 - Outcome
- K(+) channelse1
- Direction
- could not operatee1
- Value
- 100 µme1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
.jpg?width=500)
Verbatim
t0“Roots of Barley and Arabidopsis”
e1“In Arabidopsis, steady-state K(+) influx at low external K(+) concentration ([K(+)]ext = 22.5 µm) was predominantly mediated by AtAKT1 when high-affinity transport was inhibited by ammonium, whereas in barley, by contrast, K(+) channels could not operate below 100 µm”
Claim · model-written summary
Withdrawal of ammonium stimulated K(+) influx in barley at low external K(+)
- Taxon
- barleyHordeum vulgaree3
- Treatment
- Withdrawal of ammoniume3
- Outcome
- K(+) influxe3
- Direction
- stimulatione3
- Qualifier
- immediate and dramatice3
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Roots of Barley and Arabidopsis”
e3“Withdrawal of ammonium resulted in an immediate and dramatic stimulation of K(+) influx in barley, indicating a shift from active to passive K(+) uptake at low [K(+)]ext”
Claim · model-written summary
Barley root K(+) fluxes reached 36 µmol g(-1) h(-1) at 5 mm external K(+)
- Taxon
- barleyHordeum vulgaret0
- Outcome
- fluxese2
- Value
- 36 µmol g (root fresh weight)(-1) h(-1)e2
- Qualifier
- 5 mm [K(+)]exte2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Roots of Barley and Arabidopsis”
e2“yielding fluxes as high as 36 µmol g (root fresh weight)(-1) h(-1) at 5 mm [K(+)]ext, among the highest transporter-mediated K(+) fluxes hitherto reported”
Claim · model-written summary
The ammonium-withdrawal effect on K(+) uptake was established in all Arabidopsis lines at low external K(+)
- Taxon
- ArabidopsisArabidopsise4
- Material
- the wild types, atakt1, athak5, and athak5 atakt1e4
- Outcome
- ammonium-withdrawal effecte4
- Setting
- low [K(+)]exte4
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Roots of Barley and Arabidopsis”
e4“This ammonium-withdrawal effect was also established in all Arabidopsis lines (the wild types, atakt1, athak5, and athak5 atakt1) at low [K(+)]ext”
Claim · model-written summary
Ammonium withdrawal coincided with suppressed K(+) efflux in Arabidopsis genotypes except athak5 atakt1
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- ammonium-withdrawale5
- Outcome
- K(+) effluxe5
- Direction
- suppressione5
- Qualifier
- in all genotypes except athak5 atakt1e5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Roots of Barley and Arabidopsis”
e5“The ammonium-withdrawal effect coincided with a suppression of K(+) efflux and a significant hyperpolarization of the plasma membrane in all genotypes except athak5 atakt1, could be sustained over 24 h, and resulted in increased tissue K(+) accumulation”
Claim · model-written summary
Ammonium withdrawal coincided with significant hyperpolarization of the plasma membrane in Arabidopsis genotypes
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- ammonium-withdrawale5
- Outcome
- plasma membranee5
- Direction
- hyperpolarizatione5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Roots of Barley and Arabidopsis”
e5“The ammonium-withdrawal effect coincided with a suppression of K(+) efflux and a significant hyperpolarization of the plasma membrane in all genotypes except athak5 atakt1, could be sustained over 24 h, and resulted in increased tissue K(+) accumulation”
Claim · model-written summary
The ammonium-withdrawal effect could be sustained over 24 h in Arabidopsis
- Taxon
- ArabidopsisArabidopsist0
- Outcome
- ammonium-withdrawal effecte5
- Direction
- could be sustainede5
- Qualifier
- over 24 he5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Roots of Barley and Arabidopsis”
e5“The ammonium-withdrawal effect coincided with a suppression of K(+) efflux and a significant hyperpolarization of the plasma membrane in all genotypes except athak5 atakt1, could be sustained over 24 h, and resulted in increased tissue K(+) accumulation”
Claim · model-written summary
Ammonium withdrawal increased tissue K(+) accumulation in Arabidopsis
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- ammonium-withdrawale5
- Outcome
- tissue K(+) accumulatione5
- Direction
- increasede5
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Roots of Barley and Arabidopsis”
e5“The ammonium-withdrawal effect coincided with a suppression of K(+) efflux and a significant hyperpolarization of the plasma membrane in all genotypes except athak5 atakt1, could be sustained over 24 h, and resulted in increased tissue K(+) accumulation”
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