Abstract
Nitrogen assimilation in crabgrass Digitaria sanguinalis (L.) Scop., was studied by comparing leaf extracts with isolated mesophyll cell and bundle sheath strand extracts. The results show that both nitrate and nitrate reductase are localized in mesophyll cells; glutamine synthetase is nearly equally distributed in the mesophyll and bundle sheath; approximately 67% of the glutamate synthase activity is in the bundle sheath and 33% is in the mesophyll; and 80% of the glutamate dehydrogenase activity is in the bundle sheath, with the NADH-dependent form exhibiting a 2.5-fold higher activity than the NADPH-dependent form.Isolated crabgrass mesophyll cells reduce NO(2) (-) coupled to the photochemical production of O(2) but are inactive with NO(3) (-). The NO(2) (-) -dependent O(2) evolution is light-dependent; inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea; stimulated by photophosphorylation uncouplers; and exhibits a stoichiometry of O(2) evolved to NO(2) (-) reduced of 1.45 and 0.67 in coupled and uncoupled experiments, respectively. Isolated bundle sheath strands are inactive in O(2) evolution with NO(3) (-) or NO(2) (-).Based on these results, plus literature data, two schemes for crabgrass leaf nitrogen assimilation are presented, depending on whether the plant is using ammonium or nitrate as its nitrogen source. It is proposed that the increased nitrogen use efficiency in crabgrass and other C(4) plants is due partially to a "division of labor" between mesophyll and bundle sheath cells, where NO(3) (-) and NO(2) (-) reductase in mesophyll cells act as nitrogen reduction traps in an analogous fashion to phosphoenolpyruvate carboxylase acting as a CO(2) trap during C(4) photosynthesis.
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Claims 14
Claim · model-written summary
Nitrate and nitrate reductase were localized in crabgrass mesophyll cells.
- Taxon
- crabgrasse0
- Organ / stage
- mesophyll cellse1
- Gene
- nitrate reductasee1
- Outcome
- nitrate and nitrate reductase are localized in mesophyll cellse1
Not reportedDirection
Verbatim
e0“Nitrogen assimilation in crabgrass Digitaria sanguinalis (L.) Scop.”
e1“both nitrate and nitrate reductase are localized in mesophyll cells”
Claim · model-written summary
Glutamine synthetase was nearly equally distributed between the two crabgrass cell types.
Verbatim
e0“crabgrass Digitaria sanguinalis (L.) Scop.”
e1“glutamine synthetase is nearly equally distributed in the mesophyll and bundle sheath”
Claim · model-written summary
About 67% of crabgrass glutamate synthase activity was in bundle sheath and 33% in mesophyll.
Verbatim
e0“crabgrass Digitaria sanguinalis (L.) Scop.”
e1“approximately 67% of the glutamate synthase activity is in the bundle sheath and 33% is in the mesophyll”
Claim · model-written summary
About 80% of crabgrass glutamate dehydrogenase activity was in bundle sheath.
Verbatim
e0“crabgrass Digitaria sanguinalis (L.) Scop.”
e1“80% of the glutamate dehydrogenase activity is in the bundle sheath”
Claim · model-written summary
NADH-dependent glutamate dehydrogenase activity was 2.5-fold higher than the NADPH-dependent form.
Verbatim
e0“crabgrass Digitaria sanguinalis (L.) Scop.”
e1“the NADH-dependent form exhibiting a 2.5-fold higher activity than the NADPH-dependent form”
Claim · model-written summary
Isolated crabgrass mesophyll cells reduced nitrite with oxygen evolution but were inactive with nitrate.
- Taxon
- crabgrasse0
- Organ / stage
- mesophyll cellse0
- Outcome
- reduce NO(2) (-) coupled to the photochemical production of O(2)e0
Not reportedDirection
Verbatim
e0“Isolated crabgrass mesophyll cells reduce NO(2) (-) coupled to the photochemical production of O(2) but are inactive with NO(3) (-).”
Claim · model-written summary
Nitrite-dependent oxygen evolution in crabgrass mesophyll cells was light-dependent.
- Taxon
- crabgrasse0
- Organ / stage
- mesophyll cellse0
- Treatment
- lighte1
- Outcome
- NO(2) (-) -dependent O(2) evolutione1
Not reportedDirection
Verbatim
e0“Isolated crabgrass mesophyll cells”
e1“The NO(2) (-) -dependent O(2) evolution is light-dependent”
Claim · model-written summary
The inhibitor DCMU inhibited nitrite-dependent oxygen evolution.
- Taxon
- crabgrasse0
- Treatment
- 3-(3,4-dichlorophenyl)-1,1-dimethylureae1
- Outcome
- NO(2) (-) -dependent O(2) evolutione1
- Direction
- inhibitede1
Not reportedComparator
Verbatim
e0“Isolated crabgrass mesophyll cells”
e1“The NO(2) (-) -dependent O(2) evolution is light-dependent; inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea”
Claim · model-written summary
Photophosphorylation uncouplers stimulated nitrite-dependent oxygen evolution.
- Taxon
- crabgrasse0
- Treatment
- photophosphorylation uncouplerse1
- Outcome
- NO(2) (-) -dependent O(2) evolutione1
- Direction
- stimulatede1
Not reportedComparator
Verbatim
e0“Isolated crabgrass mesophyll cells”
e1“The NO(2) (-) -dependent O(2) evolution is light-dependent; inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea; stimulated by photophosphorylation uncouplers”
Claim · model-written summary
Oxygen evolved per nitrite reduced was 1.45 in coupled experiments.
Verbatim
e0“Isolated crabgrass mesophyll cells”
e1“a stoichiometry of O(2) evolved to NO(2) (-) reduced of 1.45 and 0.67 in coupled and uncoupled experiments, respectively”
Claim · model-written summary
Oxygen evolved per nitrite reduced was 0.67 in uncoupled experiments.
Verbatim
e0“Isolated crabgrass mesophyll cells”
e1“a stoichiometry of O(2) evolved to NO(2) (-) reduced of 1.45 and 0.67 in coupled and uncoupled experiments, respectively”
Claim · model-written summary
Crabgrass bundle sheath strands were inactive in oxygen evolution with nitrate or nitrite.
- Taxon
- crabgrasse1
- Organ / stage
- bundle sheath strandse0
- Outcome
- inactive in O(2) evolution with NO(3) (-) or NO(2) (-)e0
Not reportedDirection
Verbatim
e0“Isolated bundle sheath strands are inactive in O(2) evolution with NO(3) (-) or NO(2) (-).”
e1“crabgrass Digitaria sanguinalis (L.) Scop.”
Claim · model-written summary
The authors proposed distinct nitrogen-assimilation schemes for ammonium and nitrate use in crabgrass.
Verbatim
e0“two schemes for crabgrass leaf nitrogen assimilation are presented, depending on whether the plant is using ammonium or nitrate as its nitrogen source”
Claim · model-written summary
The authors proposed that cell division of labor partly explains greater nitrogen use efficiency in crabgrass and other C4 plants.
Verbatim
e0“increased nitrogen use efficiency in crabgrass and other C(4) plants is due partially to a "division of labor" between mesophyll and bundle sheath cells”