Abstract
The basis of inhibition of photosynthesis by single acute O(3) exposures was investigated in vivo using analyses based on leaf gas exchange measurements. The fully expanded second leaves of wheat plants (Triticum aestivum L. cv Avalon) were fumigated with either 200 or 400 nanomoles per mole O(3) for between 4 and 16 hours. This reduced significantly the light-saturated rate of CO(2) uptake and was accompanied by a parallel decrease in stomatal conductance. However, the stomatal limitation, estimated from the relationship between CO(2) uptake and the internal CO(2) concentration, only increased significantly during the first 8 hours of exposure to 400 nanomoles per mole O(3); no significant increase occurred for any of the other treatments. Analysis of the response of CO(2) uptake to the internal CO(2) concentration implied that the predominant factor responsible for the reduction in light-saturated CO(2) uptake was a decrease in the efficiency of carboxylation. This was 58 and 21% of the control value after 16 hours at 200 and 400 nanomoles per mole O(3), respectively. At saturating concentrations of CO(2), photosynthesis was inhibited by no more than 22% after 16 hours, indicating that the capacity for regeneration of ribulose bisphosphate was less susceptible to O(3). Ozone fumigations also had a less pronounced effect on light-limited photosynthesis. The maximum quantum yield of CO(2) uptake and the quantum yield of oxygen evolution showed no significant decline after 16 hours with 200 nanomoles per mole O(3), requiring 8 hours at 400 nanomoles per mole O(3) before a significant reduction occurred. The photochemical efficiency of photosystem II estimated from the ratio of variable to maximum chlorophyll fluorescence and the atrazine-binding capacity of isolated thylakoids demonstrated that photochemical reactions were not responsible for the initial inhibition of CO(2) uptake. The results suggest that the apparent carboxylation efficiency appears to be the initial cause of decline in photosynthesis in vivo following acute O(3) fumigation.
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Claims 13
Claim · model-written summary
Ozone significantly reduced light-saturated CO2 uptake in wheat.
- Taxon
- wheat
Triticum aestivumt0 - Treatment
- Ozonet0
- Outcome
- light-saturated rate of CO(2) uptakee0
- Direction
- reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“This reduced significantly the light-saturated rate of CO(2) uptake”
t0“Wheat following Short-Term Exposure to Ozone”
Claim · model-written summary
Ozone exposure decreased stomatal conductance.
- Taxon
- WheatTriticum aestivumt0
- Treatment
- Ozonet0
- Outcome
- stomatal conductancee0
- Direction
- decreasee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“was accompanied by a parallel decrease in stomatal conductance”
t0“Wheat following Short-Term Exposure to Ozone”
Claim · model-written summary
Stomatal limitation increased significantly only during the first eight hours at 400 nanomoles per mole ozone.
- Taxon
- WheatTriticum aestivumt0
- Treatment
- 400 nanomoles per mole O(3)e0
- Outcome
- stomatal limitatione0
- Direction
- increasede0
- Qualifier
- first 8 hourse0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the stomatal limitation, estimated from the relationship between CO(2) uptake and the internal CO(2) concentration, only increased significantly during the first 8 hours of exposure to 400 nanomoles per mole O(3)”
t0“Wheat”
Claim · model-written summary
Other ozone treatments did not significantly increase stomatal limitation.
- Taxon
- WheatTriticum aestivumt0
- Treatment
- other treatmentse0
- Outcome
- stomatal limitatione1
- Direction
- no significant increasee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“no significant increase occurred for any of the other treatments.”
e1“the stomatal limitation, estimated from the relationship between CO(2) uptake and the internal CO(2) concentration”
t0“Wheat”
Claim · model-written summary
Reduced carboxylation efficiency was inferred as the predominant cause of lower light-saturated uptake.
- Taxon
- WheatTriticum aestivumt0
- Outcome
- reduction in light-saturated CO(2) uptakee0
- Qualifier
- decrease in the efficiency of carboxylatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the predominant factor responsible for the reduction in light-saturated CO(2) uptake was a decrease in the efficiency of carboxylation.”
t0“Wheat”
Claim · model-written summary
Carboxylation efficiency reached 58% of control after 16 hours at 200 nanomoles per mole ozone.
- Taxon
- WheatTriticum aestivumt0
- Treatment
- 200e0
- Outcome
- efficiency of carboxylatione0
- Direction
- decreasee0
- Value
- 58e0
- Comparator
- controle0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the predominant factor responsible for the reduction in light-saturated CO(2) uptake was a decrease in the efficiency of carboxylation. This was 58 and 21% of the control value after 16 hours at 200 and 400 nanomoles per mole O(3), respectively.”
t0“Wheat following Short-Term Exposure to Ozone”
Claim · model-written summary
Carboxylation efficiency reached 21% of control after 16 hours at 400 nanomoles per mole ozone.
- Taxon
- WheatTriticum aestivumt0
- Treatment
- 400 nanomoles per mole O(3)e0
- Outcome
- efficiency of carboxylatione0
- Direction
- decreasee0
- Value
- 21%e0
- Comparator
- controle0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the predominant factor responsible for the reduction in light-saturated CO(2) uptake was a decrease in the efficiency of carboxylation. This was 58 and 21% of the control value after 16 hours at 200 and 400 nanomoles per mole O(3), respectively.”
t0“Wheat following Short-Term Exposure to Ozone”
Claim · model-written summary
At saturating CO2, ozone inhibited photosynthesis by at most 22% after 16 hours.
- Taxon
- WheatTriticum aestivumt0
- Treatment
- Ozonet0
- Outcome
- photosynthesise0
- Direction
- inhibitede0
- Value
- 22%e0
- Qualifier
- At saturating concentrations of CO(2)e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At saturating concentrations of CO(2), photosynthesis was inhibited by no more than 22% after 16 hours”
t0“Wheat following Short-Term Exposure to Ozone”
Claim · model-written summary
Ozone had a less pronounced effect on light-limited photosynthesis.
- Taxon
- WheatTriticum aestivumt0
- Treatment
- Ozone fumigationse0
- Outcome
- light-limited photosynthesise0
- Direction
- less pronouncede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Ozone fumigations also had a less pronounced effect on light-limited photosynthesis.”
t0“Wheat”
Claim · model-written summary
Maximum quantum yield of CO2 uptake showed no significant decline after 16 hours at 200 nanomoles per mole ozone.
- Taxon
- WheatTriticum aestivumt0
- Treatment
- 200 nanomoles per mole O(3)e0
- Outcome
- maximum quantum yield of CO(2) uptakee0
- Direction
- no significant declinee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The maximum quantum yield of CO(2) uptake and the quantum yield of oxygen evolution showed no significant decline after 16 hours with 200 nanomoles per mole O(3)”
t0“Wheat”
Claim · model-written summary
Quantum yield of oxygen evolution showed no significant decline after 16 hours at 200 nanomoles per mole ozone.
- Taxon
- WheatTriticum aestivumt0
- Treatment
- 200 nanomoles per mole O(3)e0
- Outcome
- quantum yield of oxygen evolutione0
- Direction
- no significant declinee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The maximum quantum yield of CO(2) uptake and the quantum yield of oxygen evolution showed no significant decline after 16 hours with 200 nanomoles per mole O(3)”
t0“Wheat”
Claim · model-written summary
At 400 nanomoles per mole ozone, quantum yields required eight hours before significant reduction.
- Taxon
- WheatTriticum aestivumt0
- Treatment
- 400 nanomoles per mole O(3)e0
- Outcome
- quantum yielde1
- Direction
- reductione0
- Qualifier
- 8 hourse0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“requiring 8 hours at 400 nanomoles per mole O(3) before a significant reduction occurred.”
e1“The maximum quantum yield of CO(2) uptake and the quantum yield of oxygen evolution”
t0“Wheat”
Claim · model-written summary
Photochemical measures indicated photochemistry did not cause initial CO2 uptake inhibition.
- Taxon
- WheatTriticum aestivumt0
- Outcome
- initial inhibition of CO(2) uptakee0
- Qualifier
- photochemical reactions were not responsiblee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“photochemical reactions were not responsible for the initial inhibition of CO(2) uptake.”
t0“Wheat”
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