Abstract
Expression of one specific isoform of plastidic glucose 6-phosphate dehydrogenase (G6PDH) was manipulated in transgenic tobacco. Antisense and sense constructs of the endogenous P2 form of G6PDH were used to transform plants under the control of the cauliflower mosaic virus (CaMV) 35S promotor. Recombinant plants with altered expression were taken through to homozygosity by selective screening. Northern analyses revealed substantial changes in the expression of the P2 form of G6PDH, with no apparent impact on the activity of the cytosolic isoenzyme. Analysis of G6PDH activity in chloroplasts showed that despite the large changes in expression of P2-G6PDH, the range of enzyme activity varied only from approximately 50 to 200% of the wild type, reflecting the presence of a second G6PDH chloroplastic isoform (P1). Although none of the transgenic plants showed any visible phenotype, there were marked differences in metabolism of both sense and antisense lines when compared with wild-type/control lines. Sucrose, glucose and fructose contents of leaves were higher in antisense lines, whereas in overexpressing lines, the soluble sugar content was reduced below that of control plants. Even more striking was the observation that contents of glucose 6-phosphate (Glc6P) and 6-phosphogluconate (6PG) changed, such that the ratio of Glc6P:6PG was some 2.5-fold greater in the most severe antisense lines, compared with those with the highest levels of overexpression. Because of the distinctive biochemical properties of P2-G6PDH, we investigated the impact of altered expression on the contents of antioxidants and the response of plants to oxidative stress induced by methyl viologen (MV). Plants with decreased expression of P2-G6PDH showed increased content of reduced glutathione (GSH) compared to other lines. They also possessed elevated contents of ascorbate and exhibited a much higher ratio of reduced:oxidised ascorbate. When exposed to MV, leaf discs of wild-type and overexpressing lines demonstrated increased oxidative damage as measured by lipid peroxidation. Remarkably, leaf discs from plants with decreased P2-G6PDH did not show any change in lipid peroxidation in response to increasing concentrations of up to 15 micro m MV. The results are discussed from the perspective of the role of G6PDH in carbohydrate metabolism and oxidative stress. It is suggested that the activity of P2-G6PDH may be crucial in balancing the redox poise in chloroplasts.
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Claims 12
Claim · model-written summary
Altered P2 expression did not apparently change cytosolic isoenzyme activity.
- Taxon
- tobacco (Nicotiana tabacum cv. Samsun)
Nicotiana tabacumt0 - Gene
- P2 form of G6PDHe0
- Outcome
- activity of the cytosolic isoenzymee0
- Direction
- no apparent impacte0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Northern analyses revealed substantial changes in the expression of the P2 form of G6PDH, with no apparent impact on the activity of the cytosolic isoenzyme.”
t0“tobacco (Nicotiana tabacum cv. Samsun)”
Claim · model-written summary
Despite large P2 expression changes, chloroplast G6PDH activity ranged from approximately 50 to 200% of wild type.
- Taxon
- tobacco (Nicotiana tabacum cv. Samsun)Nicotiana tabacumt0
- Gene
- P2-G6PDHe0
- Outcome
- enzyme activitye0
- Direction
- variede0
- Value
- 50 to 200%e0
- Comparator
- wild typee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“despite the large changes in expression of P2-G6PDH, the range of enzyme activity varied only from approximately 50 to 200% of the wild type”
t0“tobacco (Nicotiana tabacum cv. Samsun)”
Claim · model-written summary
Transgenic plants showed no visible phenotype.
- Taxon
- tobacco (Nicotiana tabacum cv. Samsun)Nicotiana tabacumt0
- Outcome
- visible phenotypee0
- Direction
- nonee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“none of the transgenic plants showed any visible phenotype”
t0“tobacco (Nicotiana tabacum cv. Samsun)”
Claim · model-written summary
Antisense lines had higher leaf sucrose, glucose and fructose than controls.
- Taxon
- tobacco (Nicotiana tabacum cv. Samsun)Nicotiana tabacumt0
- Treatment
- antisense linese0
- Outcome
- Sucrose, glucose and fructose contents of leavese0
- Direction
- highere0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Sucrose, glucose and fructose contents of leaves were higher in antisense lines”
t0“tobacco (Nicotiana tabacum cv. Samsun)”
Claim · model-written summary
Overexpressing lines had lower soluble sugar content than controls.
- Taxon
- tobacco (Nicotiana tabacum cv. Samsun)Nicotiana tabacumt0
- Treatment
- overexpressing linese0
- Outcome
- soluble sugar contente0
- Direction
- reducede0
- Comparator
- control plantse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“in overexpressing lines, the soluble sugar content was reduced below that of control plants”
t0“tobacco (Nicotiana tabacum cv. Samsun)”
Claim · model-written summary
The Glc6P:6PG ratio was about 2.5-fold greater in severe antisense lines than in highest overexpressors.
- Taxon
- tobacco (Nicotiana tabacum cv. Samsun)Nicotiana tabacumt0
- Material
- most severe antisense linese0
- Outcome
- ratio of Glc6P:6PGe0
- Direction
- greatere0
- Value
- 2.5-folde0
- Comparator
- those with the highest levels of overexpressione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the ratio of Glc6P:6PG was some 2.5-fold greater in the most severe antisense lines, compared with those with the highest levels of overexpression”
t0“tobacco (Nicotiana tabacum cv. Samsun)”
Claim · model-written summary
Reduced P2-G6PDH expression increased reduced glutathione relative to other lines.
- Taxon
- tobacco (Nicotiana tabacum cv. Samsun)Nicotiana tabacumt0
- Gene
- P2-G6PDHe0
- Outcome
- content of reduced glutathione (GSH)e0
- Direction
- increasede0
- Comparator
- other linese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Plants with decreased expression of P2-G6PDH showed increased content of reduced glutathione (GSH) compared to other lines.”
t0“tobacco (Nicotiana tabacum cv. Samsun)”
Claim · model-written summary
Reduced P2-G6PDH expression elevated ascorbate content.
- Taxon
- tobacco (Nicotiana tabacum cv. Samsun)Nicotiana tabacumt0
- Outcome
- contents of ascorbatee0
- Direction
- elevatede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“They also possessed elevated contents of ascorbate”
t0“tobacco (Nicotiana tabacum cv. Samsun)”
Claim · model-written summary
Reduced P2-G6PDH expression raised the reduced to oxidised ascorbate ratio.
- Taxon
- tobacco (Nicotiana tabacum cv. Samsun)Nicotiana tabacumt0
- Outcome
- ratio of reduced:oxidised ascorbatee0
- Direction
- highere0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“exhibited a much higher ratio of reduced:oxidised ascorbate”
t0“tobacco (Nicotiana tabacum cv. Samsun)”
Claim · model-written summary
Methyl viologen increased lipid peroxidation in wild-type and overexpressing leaf discs.
- Taxon
- tobacco (Nicotiana tabacum cv. Samsun)Nicotiana tabacumt0
- Material
- wild-type and overexpressing linese0
- Treatment
- MVe0
- Outcome
- lipid peroxidatione0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“When exposed to MV, leaf discs of wild-type and overexpressing lines demonstrated increased oxidative damage as measured by lipid peroxidation.”
t0“tobacco (Nicotiana tabacum cv. Samsun)”
Claim · model-written summary
Increasing methyl viologen up to 15 micro m did not change lipid peroxidation in discs with decreased P2-G6PDH.
- Taxon
- tobacco (Nicotiana tabacum cv. Samsun)Nicotiana tabacumt0
- Treatment
- increasing concentrations of up to 15 micro m MVe0
- Gene
- P2-G6PDHe0
- Outcome
- lipid peroxidatione0
- Direction
- did not show any changee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“leaf discs from plants with decreased P2-G6PDH did not show any change in lipid peroxidation in response to increasing concentrations of up to 15 micro m MV”
t0“tobacco (Nicotiana tabacum cv. Samsun)”
Claim · model-written summary
The authors suggest P2-G6PDH activity may be crucial for chloroplast redox balance.
- Taxon
- tobacco (Nicotiana tabacum cv. Samsun)Nicotiana tabacumt0
- Gene
- P2-G6PDHe0
- Outcome
- redox poise in chloroplastse0
- Qualifier
- may be cruciale0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the activity of P2-G6PDH may be crucial in balancing the redox poise in chloroplasts”
t0“tobacco (Nicotiana tabacum cv. Samsun)”
The same questions in other papers
paraquat dichloride · physiology: oxidative · Nicotiana tabacum (tobacco)Results agree
2 papers in the same direction as this paper
- positive
- positive
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.