Abstract
Ammonia assimilation by the plastidic glutamine synthetase/glutamate synthase system requires 2-oxoglutarate (2-OG) as a carbon precursor. Plastids depend on 2-OG import from the cytosol. A plastidic dicarboxylate translocator 1-[2-OG/malate translocator (DiT1)] has been identified and its substrate specificity and kinetic constants have been analyzed in vitro. However, the role of DiT1 in intact plants and its significance for ammonia assimilation remained uncertain. Here, to study the role of DiT1 in intact plants, its expression was antisense-repressed in transgenic tobacco plants. This resulted in a reduced transport capacity for 2-OG across the plastid envelope membrane. In consequence, allocation of carbon precursors to amino acid synthesis was impaired, organic acids accumulated and protein content, photosynthetic capacity and sugar pools in leaves were strongly decreased. The phenotype was consistent with a role of DIT1 in both, primary ammonia assimilation and the re-assimilation of ammonia resulting from the photorespiratory carbon cycle. Unexpectedly, the in situ rate of nitrate reduction was extremely low in alpha-DiT1 leaves, although nitrate reductase (NR) expression and activity remained high. We hypothesize that this discrepancy between extractable NR activity and in situ nitrate reduction is due to substrate limitation of NR. These findings and the severe phenotype of the antisense plants point to a crucial role of DiT1 at the interface between carbon and nitrogen metabolism.
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Claims 8
Claim · model-written summary
Antisense repression of DiT1 in tobacco reduced the transport capacity for 2-OG across the plastid envelope.
- Taxon
- tobacco
Nicotiana tabacume2 - Treatment
- antisense-repressede2
- Gene
- DiT1e2
- Outcome
- transport capacity for 2-OG across the plastid envelope membranee3
- Direction
- reducede3
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e2“Here, to study the role of DiT1 in intact plants, its expression was antisense-repressed in transgenic tobacco plants”
e3“This resulted in a reduced transport capacity for 2-OG across the plastid envelope membrane”
Claim · model-written summary
Antisense repression of DiT1 in tobacco impaired allocation of carbon precursors to amino acid synthesis.
- Taxon
- tobaccoNicotiana tabacume2
- Treatment
- antisense-repressede2
- Outcome
- allocation of carbon precursors to amino acid synthesise4
- Direction
- impairede4
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e2“Here, to study the role of DiT1 in intact plants, its expression was antisense-repressed in transgenic tobacco plants”
e4“In consequence, allocation of carbon precursors to amino acid synthesis was impaired, organic acids accumulated and protein content, photosynthetic capacity and sugar pools in leaves were strongly decreased”
Claim · model-written summary
Antisense repression of DiT1 in tobacco led to accumulation of organic acids.
- Taxon
- tobaccoNicotiana tabacume2
- Treatment
- antisense-repressede2
- Outcome
- organic acidse4
- Direction
- accumulatede4
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e2“Here, to study the role of DiT1 in intact plants, its expression was antisense-repressed in transgenic tobacco plants”
e4“In consequence, allocation of carbon precursors to amino acid synthesis was impaired, organic acids accumulated and protein content, photosynthetic capacity and sugar pools in leaves were strongly decreased”
Claim · model-written summary
Antisense repression of DiT1 in tobacco strongly decreased protein content, photosynthetic capacity and sugar pools in leaves.
- Taxon
- tobaccoNicotiana tabacume2
- Organ / stage
- leavese4
- Treatment
- antisense-repressede2
- Outcome
- protein content, photosynthetic capacity and sugar poolse4
- Direction
- strongly decreasede4
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e2“Here, to study the role of DiT1 in intact plants, its expression was antisense-repressed in transgenic tobacco plants”
e4“In consequence, allocation of carbon precursors to amino acid synthesis was impaired, organic acids accumulated and protein content, photosynthetic capacity and sugar pools in leaves were strongly decreased”
Claim · model-written summary
The in situ rate of nitrate reduction was lower in alpha-DiT1 tobacco leaves.
- Taxon
- tobaccoNicotiana tabacume2
- Material
- alpha-DiT1e5
- Outcome
- in situ rate of nitrate reductione5
- Direction
- lowerinferrede5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e2“Here, to study the role of DiT1 in intact plants, its expression was antisense-repressed in transgenic tobacco plants”
e5“Unexpectedly, the in situ rate of nitrate reduction was extremely low in alpha-DiT1 leaves, although nitrate reductase (NR) expression and activity remained high”
Claim · model-written summary
Nitrate reductase expression and activity remained unchanged in alpha-DiT1 tobacco leaves.
- Taxon
- tobaccoNicotiana tabacume2
- Material
- alpha-DiT1e5
- Gene
- nitrate reductasee5
- Outcome
- nitrate reductase (NR) expression and activitye5
- Direction
- no_changeinferrede5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e2“Here, to study the role of DiT1 in intact plants, its expression was antisense-repressed in transgenic tobacco plants”
e5“Unexpectedly, the in situ rate of nitrate reduction was extremely low in alpha-DiT1 leaves, although nitrate reductase (NR) expression and activity remained high”
Claim · model-written summary
The discrepancy between extractable NR activity and in situ nitrate reduction is hypothesized to be due to substrate limitation of NR.
- Taxon
- tobaccoNicotiana tabacume2
- Gene
- NRe6
- Outcome
- discrepancy between extractable NR activity and in situ nitrate reductione6
- Qualifier
- substrate limitatione6
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e2“Here, to study the role of DiT1 in intact plants, its expression was antisense-repressed in transgenic tobacco plants”
e6“We hypothesize that this discrepancy between extractable NR activity and in situ nitrate reduction is due to substrate limitation of NR”
Claim · model-written summary
The phenotype of DiT1 antisense tobacco is consistent with a role of DIT1 in primary ammonia assimilation and re-assimilation of photorespiratory ammonia.
- Taxon
- tobaccoNicotiana tabacume2
- Gene
- DIT1e7
- Outcome
- primary ammonia assimilatione7
- Qualifier
- the re-assimilation of ammonia resulting from the photorespiratory carbon cyclee7
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e2“Here, to study the role of DiT1 in intact plants, its expression was antisense-repressed in transgenic tobacco plants”
e7“The phenotype was consistent with a role of DIT1 in both, primary ammonia assimilation and the re-assimilation of ammonia resulting from the photorespiratory carbon cycle”
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See all 10 papers →Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.