Abstract
Photosynthesis of leaf discs from transgenic tobacco plants (Nicotiana tabacum) that express a chimeric gene that encodes chloroplast-localized Cu/Zn superoxide dismutase (SOD+) was protected from oxidative stress caused by exposure to high light intensity and low temperature. Under the same conditions, leaf discs of plants that did not express the pea SOD isoform (SOD-) had substantially lower photosynthetic rates. Young plants of both genotypes were more sensitive to oxidative stress than mature plants, but SOD+ plants retained higher photosynthetic rates than SOD- plants at all developmental stages tested. Not surprisingly, SOD+ plants had approximately 3-fold higher SOD specific activity than SOD- plants. However, SOD+ plants also exhibited a 3- to 4-fold increase in ascorbate peroxidase (APX) specific activity and had a corresponding increase in levels of APX mRNA. Dehydroascorbate reductase and glutathione reductase specific activities were the same in both SOD+ and SOD- plants. These results indicate that transgenic tobacco plants that overexpress pea Cu/Zn SOD II can compensate for the increased levels of SOD with increased expression of the H2O2-scavenging enzyme APX. Therefore, the enhancement of the active oxygen-scavenging system that leads to increased oxidative stress protection in SOD+ plants could result not only from increased SOD levels but from the combined increases in SOD and APX activity.
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Claims 9
Claim · model-written summary
SOD-expressing tobacco leaf discs retained photosynthesis under high light and low temperature oxidative stress relative to nonexpressing discs.
- Taxon
- Nicotiana tabacum
Nicotiana tabacume0 - Material
- SOD+e0
- Treatment
- high light intensity and low temperaturee0
- Gene
- Cu/Zn superoxide dismutasee0
- Outcome
- photosynthetic ratese0
- Direction
- substantially lowere0
- Comparator
- SOD-e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Photosynthesis of leaf discs from transgenic tobacco plants (Nicotiana tabacum) that express a chimeric gene that encodes chloroplast-localized Cu/Zn superoxide dismutase (SOD+) was protected from oxidative stress caused by exposure to high light intensity and low temperature. Under the same conditions, leaf discs of plants that did not express the pea SOD isoform (SOD-) had substantially lower photosynthetic rates.”
Claim · model-written summary
Young tobacco plants of both genotypes were more sensitive to oxidative stress than mature plants.
Verbatim
e0“Young plants of both genotypes were more sensitive to oxidative stress than mature plants”
Claim · model-written summary
SOD-expressing tobacco retained higher photosynthetic rates than nonexpressing plants at every tested developmental stage.
Verbatim
e0“SOD+ plants retained higher photosynthetic rates than SOD- plants at all developmental stages tested”
Claim · model-written summary
SOD specific activity in SOD-expressing tobacco was about threefold that in nonexpressing plants.
Verbatim
e0“SOD+ plants had approximately 3-fold higher SOD specific activity than SOD- plants”
Claim · model-written summary
SOD-expressing tobacco had threefold to fourfold greater APX specific activity.
Verbatim
e0“SOD+ plants also exhibited a 3- to 4-fold increase in ascorbate peroxidase (APX) specific activity”
Claim · model-written summary
APX mRNA levels increased in SOD-expressing tobacco.
Verbatim
e0“SOD+ plants also exhibited a 3- to 4-fold increase in ascorbate peroxidase (APX) specific activity and had a corresponding increase in levels of APX mRNA”
Claim · model-written summary
Dehydroascorbate reductase and glutathione reductase activities were equal in SOD-expressing and nonexpressing tobacco.
- Taxon
- plantsViridiplantaee0
- Material
- SOD+ and SOD- plantse0
- Outcome
- Dehydroascorbate reductase and glutathione reductase specific activitiese0
- Direction
- the samee0
Verbatim
e0“Dehydroascorbate reductase and glutathione reductase specific activities were the same in both SOD+ and SOD- plants”
Claim · model-written summary
The authors infer that APX induction compensates for increased SOD in transgenic tobacco.
- Taxon
- tobaccoNicotiana tabacume0
- Gene
- pea Cu/Zn SOD IIe0
- Outcome
- compensate for the increased levels of SODe0
- Qualifier
- increased expression of the H2O2-scavenging enzyme APXe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“transgenic tobacco plants that overexpress pea Cu/Zn SOD II can compensate for the increased levels of SOD with increased expression of the H2O2-scavenging enzyme APX”
Claim · model-written summary
The authors propose combined SOD and APX activity contributes to oxidative stress protection in transgenic tobacco.
Verbatim
e0“increased oxidative stress protection in SOD+ plants could result not only from increased SOD levels but from the combined increases in SOD and APX activity”
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