Abstract
BACKGROUND AND AIMS: Water is an increasingly scarce resource that limits crop productivity in many parts of the world, and the frequency and severity of drought are predicted to increase as a result of climate change. Improving tolerance to drought stress is therefore important for maximizing future crop yields. The aim of this study was to compare the effects of drought on soybean (Glycine max) leaves and nodules in order to define phenotypic markers and changes in cellular redox state that characterize the stress response in different organs, and to characterize the relationships between leaf and nodule senescence during drought. METHODS: Leaf and crown nodule metabolite pools were measured together with leaf and soil water contents, and leaf chlorophyll, total protein contents and chlorophyll a fluorescence quenching parameters in nodulated soybeans that were grown under either well-watered conditions or deprived of water for up to 21 d. KEY RESULTS: Ureides, ascorbate, protein, chlorophyll and the ratios of variable chlorophyll a fluorescence (Fv') to maximal chlorophyll a fluorescence (Fm') fell to levels below detection in the oldest leaves after 21 d of drought. While these drought-induced responses were not observed in the youngest leaf ranks, the Fv'/Fm' ratios, pyridine nucleotide levels and the reduction state of the ascorbate pool were lower in all leaf ranks after 21 d of drought. In contrast to leaves, total nodule protein, pyridine nucleotides, ureides, ascorbate and glutathione contents increased as a result of the drought treatment. However, the nodule ascorbate pool was significantly less reduced as a result of drought. Higher levels of transcripts encoding two peroxiredoxins were detected in nodules exposed to drought stress but senescence-associated transcripts and other mRNAs encoding redox-related proteins were similar under both conditions. CONCLUSIONS: While the physiological impact of the drought was perceived throughout the shoot, stress-induced senescence occurred only in the oldest leaf ranks. At this stage, a number of drought-induced changes in nodule metabolites were observed but no metabolite or transcript markers of senescence could be detected. It is concluded that stress-induced senescence in the lowest leaf ranks precedes nodule senescence, suggesting that leaves of low photosynthetic capacity are sacrificed in favour of nodule nitrogen metabolism.
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Claims 12
Claim · model-written summary
Oldest-leaf ureides, ascorbate, protein and chlorophyll fell below detection after 21 days of drought.
- Taxon
- soybean (Glycine max)
Glycine maxt0 - Organ / stage
- oldest leavese0
- Treatment
- droughte0
- Outcome
- Ureides, ascorbate, protein, chlorophylle0
- Direction
- fell to levels below detectione0
- Qualifier
- after 21 d of droughte0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Ureides, ascorbate, protein, chlorophyll and the ratios of variable chlorophyll a fluorescence (Fv') to maximal chlorophyll a fluorescence (Fm') fell to levels below detection in the oldest leaves after 21 d of drought”
t0“soybean (Glycine max)”
Claim · model-written summary
Oldest-leaf Fv′/Fm′ fell below detection after 21 days of drought.
- Taxon
- soybean (Glycine max)Glycine maxt0
- Organ / stage
- oldest leavese0
- Treatment
- droughte0
- Outcome
- ratios of variable chlorophyll a fluorescencee0
- Direction
- fell to levels below detectione0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the ratios of variable chlorophyll a fluorescence (Fv') to maximal chlorophyll a fluorescence (Fm') fell to levels below detection in the oldest leaves after 21 d of drought”
t0“soybean (Glycine max)”
Claim · model-written summary
The youngest leaf ranks did not show the oldest-leaf drought responses.
- Taxon
- soybean (Glycine max)Glycine maxt0
- Organ / stage
- youngest leaf rankse0
- Treatment
- droughte0
- Outcome
- drought-induced responsese0
- Direction
- not observede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“these drought-induced responses were not observed in the youngest leaf ranks”
t0“soybean (Glycine max)”
Claim · model-written summary
Fv′/Fm′ ratios, pyridine nucleotides and ascorbate reduction state were lower in all leaf ranks after drought.
- Taxon
- soybean (Glycine max)Glycine maxt0
- Organ / stage
- all leaf rankse0
- Treatment
- droughte0
- Outcome
- Fv'/Fm' ratios, pyridine nucleotide levels and the reduction state of the ascorbate poole0
- Direction
- lowere0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the Fv'/Fm' ratios, pyridine nucleotide levels and the reduction state of the ascorbate pool were lower in all leaf ranks after 21 d of drought”
t0“soybean (Glycine max)”
Claim · model-written summary
Total nodule protein, pyridine nucleotides and ureides increased under drought.
- Taxon
- soybean (Glycine max)Glycine maxt0
- Organ / stage
- nodulee0
- Treatment
- drought treatmente0
- Outcome
- total nodule protein, pyridine nucleotides, ureidese0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“total nodule protein, pyridine nucleotides, ureides, ascorbate and glutathione contents increased as a result of the drought treatment”
t0“soybean (Glycine max)”
Claim · model-written summary
Nodule ascorbate and glutathione contents increased under drought.
- Taxon
- soybean (Glycine max)Glycine maxt0
- Organ / stage
- nodulee0
- Treatment
- drought treatmente0
- Outcome
- ascorbate and glutathione contentse0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“total nodule protein, pyridine nucleotides, ureides, ascorbate and glutathione contents increased as a result of the drought treatment”
t0“soybean (Glycine max)”
Claim · model-written summary
The nodule ascorbate pool was significantly less reduced by drought.
- Taxon
- soybean (Glycine max)Glycine maxt0
- Treatment
- droughte0
- Outcome
- nodule ascorbate poole0
- Direction
- less reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the nodule ascorbate pool was significantly less reduced as a result of drought”
t0“soybean (Glycine max)”
Claim · model-written summary
Two nodule peroxiredoxin transcripts were higher under drought.
- Taxon
- soybean (Glycine max)Glycine maxt0
- Organ / stage
- nodulese0
- Treatment
- drought stresse0
- Outcome
- levels of transcripts encoding two peroxiredoxinse0
- Direction
- Highere0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Higher levels of transcripts encoding two peroxiredoxins were detected in nodules exposed to drought stress”
t0“soybean (Glycine max)”
Claim · model-written summary
Senescence-associated and other redox-protein transcripts were similar in both conditions.
- Taxon
- soybean (Glycine max)Glycine maxt0
- Treatment
- both conditionse0
- Outcome
- senescence-associated transcripts and other mRNAs encoding redox-related proteinse0
- Direction
- similare0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“senescence-associated transcripts and other mRNAs encoding redox-related proteins were similar under both conditions”
t0“soybean (Glycine max)”
Claim · model-written summary
Drought induced senescence only in oldest leaf ranks.
- Taxon
- soybean (Glycine max)Glycine maxt0
- Organ / stage
- oldest leaf rankse0
- Outcome
- stress-induced senescencee0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“stress-induced senescence occurred only in the oldest leaf ranks”
t0“soybean (Glycine max)”
Claim · model-written summary
No nodule metabolite or transcript senescence markers were detected at this stage.
- Taxon
- soybean (Glycine max)Glycine maxt0
- Outcome
- no metabolite or transcript markers of senescencee0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“no metabolite or transcript markers of senescence could be detected”
t0“soybean (Glycine max)”
Claim · model-written summary
Lowest-leaf senescence precedes nodule senescence.
- Taxon
- soybean (Glycine max)Glycine maxt0
- Organ / stage
- lowest leaf rankse0
- Outcome
- nodule senescencee0
- Direction
- precedese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“stress-induced senescence in the lowest leaf ranks precedes nodule senescence”
t0“soybean (Glycine max)”
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