Abstract
ABSTRACT Water deficit is a very serious constraint on N 2 fixation rates and grain yield of soybean ( Glycine max Merr.). Ureides are transported from the nodules and they accumulate in the leaves during soil drying. This accumulation appears responsible for a feedback mechanism on nitrogen fixation, and it is hypothesized to result from a decreased ureide degradation in the leaf. One enzyme involved in the ureide degradation, allantoate amidohydrolase, is manganese (Mn) dependent. As Mn deficiency can occur in soils where soybean is grown, this deficiency may aggravate soybean sensitivity to water deficit. In situ ureide breakdown was measured by incubating soybean leaves in a 5 mol m − 3 allantoic acid solution for 9 h before sampling leaf discs in which remnant ureide was measured over time. In situ ureide breakdown was dramatically decreased in leaves from plants grown without Mn. At the plant level, allantoic acid application in the nutrient solution of hydroponically grown soybean resulted in a higher accumulation of ureide in leaves and lower acetylene reduction activity (ARA) by plants grown with 0 mol m − 3 Mn than those grown with 6·6 mol m − 3 Mn. Those plants grown with 6·6 mol m − 3 Mn in comparison with those grown with 52·8 mol m − 3 Mn had, in turn, higher accumulated ureide and lower ARA. To determine if Mn level also influenced N 2 fixation sensitivity to water deficit, a dry‐down experiment was carried out by slowly dehydrating plants that were grown in soil under four different Mn nutritions. Plants receiving no Mn had the lowest leaf Mn concentration, 11·9 mg kg − 1 , and had N 2 fixation more sensitive to water deficit than plants treated with Mn in which leaf Mn concentration was in the range of 21–33 mg kg − 1 . The highest Mn treatments increased leaf Mn concentration to 37·5 mg kg − 1 and above but did not delay the decline of ARA with soil drying, although these plants showed a significant increase in ARA under well‐watered conditions.
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Claims 10
Claim · model-written summary
Soybean leaves from plants without manganese had dramatically decreased ureide breakdown.
Not reportedTaxonComparator
Verbatim
e0“In situ ureide breakdown was dramatically decreased in leaves from plants grown without Mn.”
Claim · model-written summary
At zero versus 6.6 mol m−3 manganese, allantoic acid-fed plants had higher leaf ureide accumulation.
- Taxon
- soybean
Glycine maxe0 - Treatment
- 0 mol m − 3 Mne0
- Outcome
- accumulation of ureide in leavese0
- Direction
- highere0
- Comparator
- 6·6 mol m − 3 Mne0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“allantoic acid application in the nutrient solution of hydroponically grown soybean resulted in a higher accumulation of ureide in leaves and lower acetylene reduction activity (ARA) by plants grown with 0 mol m − 3 Mn than those grown with 6·6 mol m − 3 Mn.”
Claim · model-written summary
At zero versus 6.6 mol m−3 manganese, acetylene reduction activity was lower.
- Taxon
- soybeanGlycine maxe0
- Treatment
- 0 mol m − 3 Mne0
- Outcome
- acetylene reduction activity (ARA)e0
- Direction
- lowere0
- Comparator
- 6·6 mol m − 3 Mne0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“allantoic acid application in the nutrient solution of hydroponically grown soybean resulted in a higher accumulation of ureide in leaves and lower acetylene reduction activity (ARA) by plants grown with 0 mol m − 3 Mn than those grown with 6·6 mol m − 3 Mn.”
Claim · model-written summary
At 6.6 versus 52.8 mol m−3 manganese, leaf ureide accumulation was higher.
- Treatment
- 6·6 mol m − 3 Mne0
- Outcome
- accumulated ureidee0
- Direction
- highere0
- Comparator
- 52·8 mol m − 3 Mne0
Not reportedTaxon
Verbatim
e0“Those plants grown with 6·6 mol m − 3 Mn in comparison with those grown with 52·8 mol m − 3 Mn had, in turn, higher accumulated ureide and lower ARA.”
Claim · model-written summary
At 6.6 versus 52.8 mol m−3 manganese, acetylene reduction activity was lower.
Not reportedTaxon
Verbatim
e0“Those plants grown with 6·6 mol m − 3 Mn in comparison with those grown with 52·8 mol m − 3 Mn had, in turn, higher accumulated ureide and lower ARA.”
Claim · model-written summary
Plants with no manganese had the lowest leaf manganese concentration.
Not reportedTaxonComparator
Verbatim
e0“Plants receiving no Mn had the lowest leaf Mn concentration, 11·9 mg kg − 1”
Claim · model-written summary
Nitrogen fixation was more sensitive to water deficit without manganese than with manganese.
- Treatment
- water deficite0
- Outcome
- N 2 fixatione0
- Direction
- more sensitivee0
- Qualifier
- 21–33 mg kg − 1e0
- Comparator
- plants treated with Mne0
Not reportedTaxon
Verbatim
e0“had N 2 fixation more sensitive to water deficit than plants treated with Mn in which leaf Mn concentration was in the range of 21–33 mg kg − 1 .”
Claim · model-written summary
Highest manganese treatments raised leaf manganese to at least 37.5 mg kg−1.
- Treatment
- highest Mn treatmentse0
- Outcome
- leaf Mn concentratione0
- Direction
- increasede0
- Value
- 37·5 mg kg − 1 and abovee0
Not reportedTaxonComparator
Verbatim
e0“The highest Mn treatments increased leaf Mn concentration to 37·5 mg kg − 1 and above”
Claim · model-written summary
Highest manganese treatments did not delay the decline in acetylene reduction with soil drying.
Not reportedTaxonComparator
Verbatim
e0“did not delay the decline of ARA with soil drying”
Claim · model-written summary
Highest manganese treatments significantly increased acetylene reduction under well-watered conditions.
Not reportedTaxonTreatmentComparator
Verbatim
e0“these plants showed a significant increase in ARA under well‐watered conditions.”
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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.