Abstract
During ear development in maize (Zea mays L.), nitrogenous compounds are translocated from vegetative organs to the kernels. At anthesis, the stalk contains approximately 40% of the total plant N, and contributes 45% of the N remobilized to the ear. Therefore, the stalk has an important function as a temporary reservoir for N. Little is known of the metabolism of maize stalks, and this paper describes initial studies of enzymes of N metabolism. High in vitro activity of glutamine synthetase (GS) in maize stalk samples throughout ear development contrasted with a peak in activity of glutamate synthase soon after anthesis and negligible nitrate reductase. With fresh sections of stalk tissue collected at anthesis, (15)N-feeding experiments confirmed high GS and low nitrate reductase activities. Two isoforms of GS were separated from extracts from stalk tissue: GS1, the cytoplasmic form, increased to maximum levels at 2 weeks postanthesis and remained fairly high thereafter; whereas the plastidic form, GS2, declined progressively during kernel development. Western blot analysis confirmed the presence of constantly high levels of GS protein after anthesis. The levels of GS proteins decreased after transfer of N-starved, hydroponically grown plants to N-rich conditions in order to restrict remobilization of N. In contrast, transfer of plants grown under abundant N conditions to N-free medium, which encourages N remobilization, resulted in a relative increase in GS protein. Because glutamine is the major form of N transported in maize, the results indicate that GS, specifically the GS1 isoform, has a central role in the remobilization on nitrogenous compounds from the stalk to the ear.
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Claims 12
Claim · model-written summary
At anthesis, maize stalk held about 40% of plant N.
Zea maysOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At anthesis, the stalk contains approximately 40% of the total plant N”
e1“maize (Zea mays L.)”
Claim · model-written summary
Maize stalk contributed 45% of nitrogen remobilized to the ear.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“contributes 45% of the N remobilized to the ear”
e1“maize (Zea mays L.)”
e2“At anthesis, the stalk contains approximately 40% of the total plant N”
Claim · model-written summary
Glutamine synthetase activity remained high in maize stalk during ear development.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“High in vitro activity of glutamine synthetase (GS) in maize stalk samples throughout ear development”
Claim · model-written summary
Glutamate synthase activity peaked soon after anthesis.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a peak in activity of glutamate synthase soon after anthesis”
e1“maize (Zea mays L.)”
Claim · model-written summary
Nitrate reductase activity was negligible in stalk samples.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“negligible nitrate reductase”
e1“maize stalk samples”
Claim · model-written summary
Nitrogen feeding confirmed high glutamine synthetase activity and low nitrate reductase activity in anthesis stalk sections.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“(15)N-feeding experiments confirmed high GS and low nitrate reductase activities”
e1“maize stalk samples”
e2“fresh sections of stalk tissue collected at anthesis”
Claim · model-written summary
Cytoplasmic GS1 reached maximum levels two weeks after anthesis and stayed fairly high afterward.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“GS1, the cytoplasmic form, increased to maximum levels at 2 weeks postanthesis and remained fairly high thereafter”
e1“maize stalk samples”
Claim · model-written summary
Plastidic GS2 declined progressively during kernel development.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“GS2, declined progressively during kernel development”
e1“maize stalk samples”
Claim · model-written summary
Glutamine synthetase protein levels stayed high after anthesis.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Western blot analysis confirmed the presence of constantly high levels of GS protein after anthesis”
e1“maize stalk samples”
Claim · model-written summary
Transfer from nitrogen starvation to nitrogen-rich conditions decreased GS protein levels.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The levels of GS proteins decreased after transfer of N-starved, hydroponically grown plants to N-rich conditions”
e1“maize (Zea mays L.)”
Claim · model-written summary
Transfer from abundant nitrogen to nitrogen-free medium increased GS protein levels.
- Treatment
- N-free mediume0
- Outcome
- GS proteine0
- Direction
- relative increasee0
- Comparator
- abundant N conditionse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“transfer of plants grown under abundant N conditions to N-free medium, which encourages N remobilization, resulted in a relative increase in GS protein”
e1“maize (Zea mays L.)”
Claim · model-written summary
The authors inferred a central role for GS1 in moving nitrogenous compounds from stalk to ear.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“GS, specifically the GS1 isoform, has a central role in the remobilization on nitrogenous compounds from the stalk to the ear”
e1“maize (Zea mays L.)”