Abstract
Young (16‐day‐old) Sorghum bicolor plants of a late‐ and slow‐senescing Texas A&M line (B 35) and of an early‐ and fast‐senescing descendant of an Ethiopian landrace (E 36‐1) were subjected to drought stress by decreasing the soil water content to 30% field capacity over 6 days. Plant water potentials decreased from − 2 bar (controls) to − 10 to − 18 bar, and this drought stress resulted in: (1) differential phenotypic reactions and (2) differential decreases in photosynthesis rates in the two cultivars. While E 36‐1 tended to lose viable leaf area from the leaf tips downwards, B 35 showed a gradual overall drying of the leaf. At the same time, photosynthesis rates decreased from 31.5 ± 1.6 to 12.3 ± 5.0 µmol CO 2 m −2 s −1 (E 36‐1) and from 30.5 ± 1.6 to 3.3 ± 2.6 µmol CO 2 m −2 s −1 (B 35), respectively. In vitro enzyme activities of phosphoenolpyruvate carboxylase (PEPCase), malate dehydrogenase (MDH) and malic enzyme (ME) on a leaf area basis exceeded the photosynthesis rates. Pyruvate phosphate dikinase (PPDK) activity was close to the photosynthesis rates in control plants and higher than the photosynthesis rates in drought‐stressed plants. Thus, none of the enzymes appeared to limit photosynthesis under drought stress, and likely bottleneck enzyme activities of the C3 pathway in the bundle‐sheath cells, i.e. ribulose‐1,5‐bisphosphate carboxylase (RubisCO) and stromal fructose‐1,5‐bisphosphatase (sFBPase), also showed sufficient activities to sustain higher photosynthesis rates than those observed in the stressed plants. However, under drought stress, total leaf malate concentrations were higher in B 35 (up to 33.1 µmol g −1 FW) than in E 36‐1 (up to 22.4 µmol g −1 FW). In particular, at the presumed cytosolic pH of 7.0–7.3, S. bicolor PEPCase was strongly inhibited by malate. In contrast with the in vitro PEPCase enzyme activities, the A / C i curves suggested a stronger decrease in the in vivo activity of the enzyme in B 35 under drought stress than in E 36‐1. It is therefore suggested that photosynthesis under drought stress may be inhibited differentially through feedback malate inhibition of PEPCase in S. bicolor .
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Claims 13
Claim · model-written summary
Drought decreased plant water potential from − 2 bar to − 10 to − 18 bar.
- Treatment
- drought stresse1
- Outcome
- Plant water potentialse0
- Direction
- decreasede0
- Value
- − 10 to − 18 bare0
- Qualifier
- − 2 bare0
- Comparator
- controlse0
Not reportedTaxon
Verbatim
e0“Plant water potentials decreased from − 2 bar (controls) to − 10 to − 18 bar”
e1“under drought stress, total leaf malate concentrations were higher in B 35 (up to 33.1 µmol g −1 FW) than in E 36‐1 (up to 22.4 µmol g −1 FW)”
Claim · model-written summary
E 36‐1 lost viable leaf area from leaf tips downward under drought.
Not reportedTaxon
Verbatim
e0“E 36‐1 tended to lose viable leaf area from the leaf tips downwards”
Claim · model-written summary
B 35 showed gradual drying across the leaf under drought.
Not reportedTaxon
Verbatim
e0“B 35 showed a gradual overall drying of the leaf”
Claim · model-written summary
Drought reduced photosynthesis in E 36‐1 from 31.5 ± 1.6 to 12.3 ± 5.0 µmol CO 2 m −2 s −1.
- Material
- E 36‐1e0
- Treatment
- drought stresse1
- Outcome
- photosynthesis ratese0
- Direction
- decreasede0
- Value
- 12.3 ± 5.0 µmol CO 2 m −2 s −1e0
- Qualifier
- 31.5 ± 1.6e0
Not reportedTaxonComparator
Verbatim
e0“photosynthesis rates decreased from 31.5 ± 1.6 to 12.3 ± 5.0 µmol CO 2 m −2 s −1 (E 36‐1)”
e1“under drought stress, total leaf malate concentrations were higher in B 35 (up to 33.1 µmol g −1 FW) than in E 36‐1 (up to 22.4 µmol g −1 FW)”
Claim · model-written summary
Drought reduced photosynthesis in B 35 from 30.5 ± 1.6 to 3.3 ± 2.6 µmol CO 2 m −2 s −1.
- Material
- B 35e0
- Treatment
- drought stresse1
- Outcome
- photosynthesis ratese0
- Direction
- decreasede0
- Value
- 3.3 ± 2.6 µmol CO 2 m −2 s −1e0
- Qualifier
- 30.5 ± 1.6e0
Not reportedTaxonComparator
Verbatim
e0“photosynthesis rates decreased from 31.5 ± 1.6 to 12.3 ± 5.0 µmol CO 2 m −2 s −1 (E 36‐1) and from 30.5 ± 1.6 to 3.3 ± 2.6 µmol CO 2 m −2 s −1 (B 35)”
e1“under drought stress, total leaf malate concentrations were higher in B 35 (up to 33.1 µmol g −1 FW) than in E 36‐1 (up to 22.4 µmol g −1 FW)”
Claim · model-written summary
PEPCase, MDH and ME in vitro activities exceeded photosynthesis rates on a leaf area basis.
- Gene
- phosphoenolpyruvate carboxylase (PEPCase), malate dehydrogenase (MDH) and malic enzyme (ME)e0
- Outcome
- enzyme activitiese0
- Direction
- exceedede0
- Comparator
- photosynthesis ratese0
Not reportedTaxon
Verbatim
e0“In vitro enzyme activities of phosphoenolpyruvate carboxylase (PEPCase), malate dehydrogenase (MDH) and malic enzyme (ME) on a leaf area basis exceeded the photosynthesis rates.”
Claim · model-written summary
PPDK activity was close to photosynthesis rates in controls.
- Gene
- Pyruvate phosphate dikinase (PPDK)e0
- Outcome
- activitye0
- Direction
- close toe0
- Qualifier
- control plantse0
- Comparator
- photosynthesis ratese0
Not reportedTaxon
Verbatim
e0“Pyruvate phosphate dikinase (PPDK) activity was close to the photosynthesis rates in control plants”
Claim · model-written summary
PPDK activity exceeded photosynthesis rates in drought stressed plants.
- Gene
- Pyruvate phosphate dikinase (PPDK)e1
- Outcome
- activitye1
- Direction
- higher thane0
- Qualifier
- drought‐stressed plantse0
- Comparator
- photosynthesis ratese0
Not reportedTaxon
Verbatim
e0“higher than the photosynthesis rates in drought‐stressed plants”
e1“Pyruvate phosphate dikinase (PPDK) activity was close to the photosynthesis rates in control plants”
Claim · model-written summary
RubisCO and sFBPase activities were sufficient to sustain higher photosynthesis than observed under drought.
- Gene
- ribulose‐1,5‐bisphosphate carboxylase (RubisCO) and stromal fructose‐1,5‐bisphosphatase (sFBPase)e0
- Outcome
- activitiese0
- Direction
- highere0
- Comparator
- those observed in the stressed plantse0
Not reportedTaxon
Verbatim
e0“ribulose‐1,5‐bisphosphate carboxylase (RubisCO) and stromal fructose‐1,5‐bisphosphatase (sFBPase), also showed sufficient activities to sustain higher photosynthesis rates than those observed in the stressed plants”
Claim · model-written summary
Drought stressed B 35 accumulated more leaf malate than E 36‐1, up to 33.1 versus 22.4 µmol g −1 FW.
- Material
- B 35e0
- Outcome
- total leaf malate concentrationse0
- Direction
- highere0
- Value
- up to 33.1 µmol g −1 FWe0
- Qualifier
- up to 22.4 µmol g −1 FWe0
- Comparator
- E 36‐1e0
Not reportedTaxon
Verbatim
e0“under drought stress, total leaf malate concentrations were higher in B 35 (up to 33.1 µmol g −1 FW) than in E 36‐1 (up to 22.4 µmol g −1 FW)”
Claim · model-written summary
Malate strongly inhibited Sorghum PEPCase at presumed cytosolic pH 7.0–7.3.
- Taxon
- S. bicolor
Sorghum bicolore0 - Treatment
- malatee0
- Gene
- S. bicolor PEPCasee0
- Outcome
- PEPCasee0
- Direction
- inhibitede0
- Qualifier
- presumed cytosolic pH of 7.0–7.3e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“at the presumed cytosolic pH of 7.0–7.3, S. bicolor PEPCase was strongly inhibited by malate”
Claim · model-written summary
A/Ci curves suggested a greater in vivo PEPCase activity decline in B 35 than E 36‐1 under drought.
- Material
- B 35e0
- Treatment
- drought stresse0
- Outcome
- in vivo activity of the enzymee0
- Direction
- stronger decreasee0
- Comparator
- E 36‐1e0
Not reportedTaxon
Verbatim
e0“the A / C i curves suggested a stronger decrease in the in vivo activity of the enzyme in B 35 under drought stress than in E 36‐1”
Claim · model-written summary
The authors suggest differential inhibition of drought photosynthesis through malate feedback on PEPCase.
- Taxon
- S. bicolorSorghum bicolore0
- Gene
- PEPCasee0
- Compound
- malatee0
- Outcome
- photosynthesise0
- Direction
- inhibited differentiallye0
- Qualifier
- under drought stresse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“photosynthesis under drought stress may be inhibited differentially through feedback malate inhibition of PEPCase in S. bicolor”
The same questions in other papers
drought · physiology: photosynthesis · Sorghum bicolor (sorghum)Results differ
12 papers in the same direction as this paper · 2 in the opposite direction
- no effect
- negative
- positive
11 papers more in this group
See all 15 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.