Abstract
Maize grows in nitrate-dominated dryland soils, but shortly upon localized dressing of nitrogen fertilizers, ammonium is retained as a noticeable form of nitrogen source available to roots. Thus in addition to nitrate, the absorption of ammonium can be an important strategy that promotes rapid plant growth at strong nitrogen demanding stages. The present study reports the functional characterization of three root-expressed ammonium transporters (AMTs), aiming at finding out functional and regulatory properties that correlate with efficient nitrogen acquisition of maize. Using a stable electrophysiological recording method we previously established in Xenopus laevis oocytes that integrates the capture of currents in response to voltage ramps with onsite stability controls, we demonstrate that all three ZmAMT1s engage NH4+ uniporting as ammonium uptake mechanisms. The Km value for ZmAMT1.1a, 1.1b or ZmAMT1.3 is respectively 9.9 μM, 15.6 μM or 18.6 μM, indicating a typical high-affinity transport of NH4+ ions. Importantly, the uptake currents of these ZmAMT1s are markedly amplified upon extracellular acidification. A pH drop from 7.4 to 5.4 results in a 140.8%, 64.1% or a 120.7% increase of ammonium uptake activity through ZmAMT1.1a, 1.1b or ZmAMT1.3. Since ammonium uptake by plant roots accompanies a spontaneous acidification to the root medium, the functional promotion of ZmAMT1.1a, 1.1b and ZmAMT1.3 by low pH is in line with the facilitated ammonium uptake activity in maize roots. Furthermore, the expression of the three ZmAMT1 genes is induced under ammonium-dominated conditions. Thus we describe a facilitated ammonium uptake strategy in maize roots by functional and expression regulations of ZmAMT1 transporters that may coordinate with efficient acquisition of this form of nitrogen source when available.
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Claims 8
Claim · model-written summary
All three maize ZmAMT1 transporters mediate NH4+ uniport.
Zea maysOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“all three ZmAMT1s engage NH4+ uniporting as ammonium uptake mechanisms”
t0“Maize Roots”
Claim · model-written summary
ZmAMT1.1a has a Km of 9.9 μM.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The Km value for ZmAMT1.1a, 1.1b or ZmAMT1.3 is respectively 9.9 μM, 15.6 μM or 18.6 μM”
t0“Maize Roots”
Claim · model-written summary
ZmAMT1.1b has a Km of 15.6 μM.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The Km value for ZmAMT1.1a, 1.1b or ZmAMT1.3 is respectively 9.9 μM, 15.6 μM or 18.6 μM”
t0“Maize Roots”
Claim · model-written summary
ZmAMT1.3 has a Km of 18.6 μM.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The Km value for ZmAMT1.1a, 1.1b or ZmAMT1.3 is respectively 9.9 μM, 15.6 μM or 18.6 μM”
t0“Maize Roots”
Claim · model-written summary
Lower external pH raised ZmAMT1.1a ammonium uptake activity by 140.8%.
- Treatment
- pH drop from 7.4 to 5.4e0
- Gene
- ZmAMT1.1ae0
- Outcome
- ammonium uptake activitye0
- Direction
- increasee0
- Value
- 140.8%e0
- Comparator
- 7.4e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“A pH drop from 7.4 to 5.4 results in a 140.8%, 64.1% or a 120.7% increase of ammonium uptake activity through ZmAMT1.1a, 1.1b or ZmAMT1.3”
t0“Maize Roots”
Claim · model-written summary
Lower external pH raised ZmAMT1.1b ammonium uptake activity by 64.1%.
- Treatment
- pH drop from 7.4 to 5.4e0
- Gene
- 1.1be0
- Outcome
- ammonium uptake activitye0
- Direction
- increasee0
- Value
- 64.1%e0
- Comparator
- 7.4e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“A pH drop from 7.4 to 5.4 results in a 140.8%, 64.1% or a 120.7% increase of ammonium uptake activity through ZmAMT1.1a, 1.1b or ZmAMT1.3”
t0“Maize Roots”
Claim · model-written summary
Lower external pH raised ZmAMT1.3 ammonium uptake activity by 120.7%.
- Treatment
- pH drop from 7.4 to 5.4e0
- Gene
- ZmAMT1.3e0
- Outcome
- ammonium uptake activitye0
- Direction
- increasee0
- Value
- 120.7%e0
- Comparator
- 7.4e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“A pH drop from 7.4 to 5.4 results in a 140.8%, 64.1% or a 120.7% increase of ammonium uptake activity through ZmAMT1.1a, 1.1b or ZmAMT1.3”
t0“Maize Roots”
Claim · model-written summary
Ammonium-dominated conditions induced expression of three ZmAMT1 genes.
- Treatment
- ammonium-dominated conditionse0
- Gene
- ZmAMT1e0
- Outcome
- expression of the three ZmAMT1 genese0
- Direction
- inducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“expression of the three ZmAMT1 genes is induced under ammonium-dominated conditions”
t0“Maize Roots”
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