Abstract
A feedback mechanism which involves sensing of change in phloem N concentration has been proposed to control nodulation and dinitrogen fixation in the presence of external combined N. Whether this control is in response to a change in total N or in some specific signal compound(s) is not known. In the present study we reevaluated the hypothesis that control of nodulation and N 2 fixation involves sensing of change in tissue N composition and attempted to identify potential signal molecule(s) involved. Two soybean ( Glycine max [L.] Merr.) genotypes (Williams 82 and NOD1‐3) differing in nodule number and tolerance to nitrate were germinated in sand trays. Seven‐day‐old seedlings were inoculated with a solution of Bradyrhizobium japonicum and grown for 28 days in growth chambers, using a hydroponic system with limited N supply to promote nodulation. Half of 28‐day‐old plants were treated with 15 m M NO 3 − , then control and treated plants were sampled at the onset of nitrogenase inhibition (24 h following NO 3 − , treatment) for evaluation of nitrogenase activity and tissue concentration of total N and of each individual free amino acid. Phenylisothiocyanate‐(PITC) amino acid derivatives were separated and quantified using HPLC. The decline in nitrogenase activity following the short‐term nitrate treatment was associated with a dramatic asparagine concentration increase in the shoot and an increase in nodule aspartate and glutamate in both genotypes. Asparagine concentration in the shoot increased 35 times from a barely detectable level of 95 to 3 327 nmol g −1 fresh weight in Williams 82, and more than tripled from 509 to 1 753 nmol g −1 fresh weight in NOD1‐3. Increase in levels of free Asn and in total free amino acids in the shoot following the short‐term nitrate treatment was more pronounced in Williams 82 than in its partially nitrate‐tolerant mutant NOD1‐3. These results indicate that the feedback control of nodule activity may involve sensing changes in shoot asparagine levels and/or products of its metabolism (aspartate and glutamate) in the nodule. These results also indicate that partial‐nitrate tolerance of nodulation in the hypernodulated NOD1‐3 mutant is associated with a lesser change in tissue N following nitrate treatment.
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Claims 4
Claim · model-written summary
Short-term nitrate treatment reduced nitrogenase activity in both soybean genotypes.
- Taxon
- soybean
Glycine maxt0 - Treatment
- short‐term nitrate treatmente0
- Interactor
- Bradyrhizobium japonicum
Bradyrhizobium japonicumt1symbiont - Outcome
- nitrogenase activitye0
- Direction
- declinee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The decline in nitrogenase activity following the short‐term nitrate treatment was associated with a dramatic asparagine concentration increase in the shoot and an increase in nodule aspartate and glutamate in both genotypes.”
t0“soybean”
t1“Bradyrhizobium japonicum”
Claim · model-written summary
Shoot free Asn and total free amino acids rose more in Williams 82 than NOD1‐3 after nitrate treatment.
- Taxon
- soybeanGlycine maxt0
- Material
- Williams 82e0
- Outcome
- levels of free Asn and in total free amino acids in the shoote0
- Direction
- more pronouncede0
- Comparator
- NOD1‐3e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Increase in levels of free Asn and in total free amino acids in the shoot following the short‐term nitrate treatment was more pronounced in Williams 82 than in its partially nitrate‐tolerant mutant NOD1‐3.”
t0“soybean”
Claim · model-written summary
The authors infer that nodule activity feedback may sense shoot asparagine or nodule aspartate and glutamate.
- Taxon
- soybeanGlycine maxt0
- Compound
- asparaginee0
- Outcome
- feedback control of nodule activitye0
- Qualifier
- may involve sensing changese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“feedback control of nodule activity may involve sensing changes in shoot asparagine levels and/or products of its metabolism (aspartate and glutamate) in the nodule”
t0“soybean”
Claim · model-written summary
Partial nitrate tolerance of NOD1‐3 nodulation was associated with a smaller tissue N change after nitrate.
- Taxon
- soybeanGlycine maxt0
- Material
- NOD1‐3e0
- Outcome
- partial‐nitrate tolerance of nodulatione0
- Qualifier
- a lesser change in tissue Ne0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“partial‐nitrate tolerance of nodulation in the hypernodulated NOD1‐3 mutant is associated with a lesser change in tissue N following nitrate treatment”
t0“soybean”
The same questions in other papers
nitrogen · Bradyrhizobium japonicum · Glycine max (soybean)Positive and negative results
5 papers in the same direction as this paper · 5 in the opposite direction
- positive
- positive
- positive
7 papers more in this group
See all 11 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.