Abstract
Symbiotic nitrogen fixation is sensitive to dark chilling (7 degrees C-15 degrees C)-induced inhibition in soybean (Glycine max). To characterize the mechanisms that cause the stress-induced loss of nodule function, we examined nodule structure, carbon-nitrogen interactions, and respiration in two soybean genotypes that differ in chilling sensitivity: PAN809 (PAN), which is chilling sensitive, and Highveld Top (HT), which is more chilling resistant. Nodule numbers were unaffected by dark chilling, as was the abundance of the nitrogenase and leghemoglobin proteins. However, dark chilling decreased nodule respiration rates, nitrogenase activities, and NifH and NifK mRNAs and increased nodule starch, sucrose, and glucose in both genotypes. Ureide and fructose contents decreased only in PAN nodules. While the chilling-induced decreases in nodule respiration persisted in PAN even after return to optimal temperatures, respiration started to recover in HT by the end of the chilling period. The area of the intercellular spaces in the nodule cortex and infected zone was greatly decreased in HT after three nights of chilling, an acclimatory response that was absent from PAN. These data show that HT nodules are able to regulate both respiration and the area of the intercellular spaces during chilling and in this way control the oxygen diffusion barrier, which is a key component of the nodule stress response. We conclude that chilling-induced loss of symbiotic nitrogen fixation in PAN is caused by the inhibition of respiration coupled to the failure to regulate the oxygen diffusion barrier effectively. The resultant limitations on nitrogen availability contribute to the greater chilling-induced inhibition of photosynthesis in PAN than in HT.
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Claims 12
Claim · model-written summary
Dark chilling did not alter soybean nodule number.
- Taxon
- soybean (Glycine max)
Glycine maxe1 - Treatment
- dark chillinge0
- Outcome
- Nodule numberse0
- Direction
- unaffectede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Nodule numbers were unaffected by dark chilling”
t0“Soybean”
e1“soybean (Glycine max)”
Claim · model-written summary
Dark chilling did not alter nitrogenase or leghemoglobin protein abundance.
- Taxon
- soybean (Glycine max)Glycine maxe1
- Treatment
- dark chillinge2
- Outcome
- abundance of the nitrogenase and leghemoglobin proteinse0
- Direction
- unaffectede2
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“as was the abundance of the nitrogenase and leghemoglobin proteins”
t0“Soybean”
e1“soybean (Glycine max)”
e2“Nodule numbers were unaffected by dark chilling”
Claim · model-written summary
Dark chilling reduced nodule respiration and nitrogenase activity in both genotypes.
- Taxon
- soybean (Glycine max)Glycine maxe1
- Treatment
- dark chillinge0
- Outcome
- nodule respiration rates, nitrogenase activitiese0
- Direction
- decreasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“dark chilling decreased nodule respiration rates, nitrogenase activities”
t0“Soybean”
e1“soybean (Glycine max)”
Claim · model-written summary
Dark chilling reduced NifH and NifK mRNAs in both genotypes.
- Taxon
- soybean (Glycine max)Glycine maxe1
- Treatment
- dark chillinge0
- Gene
- NifH and NifKe0
- Outcome
- NifH and NifK mRNAse0
- Direction
- decreasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“dark chilling decreased nodule respiration rates, nitrogenase activities, and NifH and NifK mRNAs”
t0“Soybean”
e1“soybean (Glycine max)”
Claim · model-written summary
Dark chilling increased nodule starch, sucrose and glucose in both genotypes.
- Taxon
- soybean (Glycine max)Glycine maxe1
- Treatment
- dark chillinge2
- Outcome
- nodule starch, sucrose, and glucosee0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“increased nodule starch, sucrose, and glucose in both genotypes”
t0“Soybean”
e1“soybean (Glycine max)”
e2“Nodule numbers were unaffected by dark chilling”
Claim · model-written summary
Ureide and fructose content declined only in PAN nodules.
- Taxon
- soybean (Glycine max)Glycine maxe1
- Material
- PANe0
- Treatment
- dark chillinge2
- Outcome
- Ureide and fructose contentse0
- Direction
- decreasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Ureide and fructose contents decreased only in PAN nodules”
t0“Soybean”
e1“soybean (Glycine max)”
e2“Nodule numbers were unaffected by dark chilling”
Claim · model-written summary
Nodule respiration remained reduced in PAN after return to optimal temperatures.
- Taxon
- soybean (Glycine max)Glycine maxe1
- Material
- PANe0
- Outcome
- nodule respiratione0
- Direction
- decreasese0
- Qualifier
- even after return to optimal temperaturese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“chilling-induced decreases in nodule respiration persisted in PAN even after return to optimal temperatures”
t0“Soybean”
e1“soybean (Glycine max)”
Claim · model-written summary
Nodule respiration began recovering in HT by the end of chilling.
- Taxon
- soybean (Glycine max)Glycine maxe1
- Material
- HTe0
- Outcome
- respiratione0
- Direction
- recovere0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“respiration started to recover in HT by the end of the chilling period”
t0“Soybean”
e1“soybean (Glycine max)”
Claim · model-written summary
Intercellular space area in HT nodules decreased greatly after three chilling nights.
- Taxon
- soybean (Glycine max)Glycine maxe1
- Material
- HTe0
- Organ / stage
- nodule cortex and infected zonee0
- Treatment
- three nights of chillinge0
- Outcome
- area of the intercellular spacese0
- Direction
- decreasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The area of the intercellular spaces in the nodule cortex and infected zone was greatly decreased in HT after three nights of chilling”
t0“Soybean”
e1“soybean (Glycine max)”
Claim · model-written summary
PAN lacked the intercellular-space acclimation observed in HT.
- Taxon
- soybean (Glycine max)Glycine maxe1
- Material
- PANe0
- Outcome
- acclimatory responsee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“an acclimatory response that was absent from PAN”
t0“Soybean”
e1“soybean (Glycine max)”
Claim · model-written summary
In PAN, inhibited respiration and failure to regulate the oxygen diffusion barrier caused chilling-induced nitrogen-fixation loss, according to the authors.
- Taxon
- soybean (Glycine max)Glycine maxe1
- Material
- PANe0
- Outcome
- loss of symbiotic nitrogen fixatione0
- Qualifier
- inhibition of respiration coupled to the failure to regulate the oxygen diffusion barrier effectivelye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“chilling-induced loss of symbiotic nitrogen fixation in PAN is caused by the inhibition of respiration coupled to the failure to regulate the oxygen diffusion barrier effectively”
t0“Soybean”
e1“soybean (Glycine max)”
Claim · model-written summary
Nitrogen limitation contributed to greater chilling-induced photosynthesis inhibition in PAN than HT.
- Taxon
- soybean (Glycine max)Glycine maxe1
- Material
- PANe0
- Outcome
- inhibition of photosynthesise0
- Qualifier
- limitations on nitrogen availabilitye0
- Comparator
- HTe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“limitations on nitrogen availability contribute to the greater chilling-induced inhibition of photosynthesis in PAN than in HT”
t0“Soybean”
e1“soybean (Glycine max)”
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