Abstract
Plants growing in dense canopies are exposed to vertical light gradients and show photosynthetic acclimation at the whole-plant level, resulting in efficient photosynthetic carbon gain. We studied the role of cytokinins transported through the transpiration stream as one of probably multiple signals for photosynthetic acclimation to light gradients using both tobacco (Nicotiana tabacum) and Arabidopsis (Arabidopsis thaliana). We show that substantial variation in leaf transpiration parallels the light gradient in tobacco canopies and experimental reduction of the transpiration rate of a leaf, independent of light, is sufficient to reduce photosynthetic capacity in both species, as well as transcript levels of the small subunit of Rubisco (rbcS) gene in Arabidopsis. Mass spectrometric analysis of xylem sap collected from intact, transpiring tobacco plants revealed that shaded leaves import less cytokinin than leaves exposed to high light. In Arabidopsis, reduced transpiration rate of a leaf in the light is associated with lower cytokinin concentrations, including the bioactive trans-zeatin and trans-zeatin riboside, as well as reduced expression of the cytokinin-responsive genes ARR7 and ARR16. External application of cytokinin to shaded leaves rescued multiple shade effects, including rbcS transcript levels in both species, as did locally induced cytokinin overproduction in transgenic tobacco plants. From these data, we conclude that light gradients over the foliage of a plant result in reduced cytokinin activity in shaded leaves as a consequence of reduced import through the xylem and that cytokinin is involved in the regulation of whole-plant photosynthetic acclimation to light gradients in canopies.
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Claims 12
Claim · model-written summary
Leaf transpiration varied in parallel with the light gradient in tobacco canopies.
- Taxon
- tobacco
Nicotiana tabacume0 - Outcome
- leaf transpiratione0
- Setting
- tobacco canopiese0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“substantial variation in leaf transpiration parallels the light gradient in tobacco canopies”
Claim · model-written summary
Experimentally reduced leaf transpiration reduced photosynthetic capacity in tobacco.
- Taxon
- tobaccoNicotiana tabacume1
- Treatment
- experimental reduction of the transpiration rate of a leafe0
- Outcome
- photosynthetic capacitye0
- Direction
- reducee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“experimental reduction of the transpiration rate of a leaf, independent of light, is sufficient to reduce photosynthetic capacity in both species”
e1“tobacco (Nicotiana tabacum)”
Claim · model-written summary
Experimentally reduced leaf transpiration reduced photosynthetic capacity in Arabidopsis.
- Taxon
- Arabidopsis
Arabidopsise1 - Treatment
- experimental reduction of the transpiration rate of a leafe0
- Outcome
- photosynthetic capacitye0
- Direction
- reducee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“experimental reduction of the transpiration rate of a leaf, independent of light, is sufficient to reduce photosynthetic capacity in both species”
e1“Arabidopsis (Arabidopsis thaliana)”
Claim · model-written summary
Reduced transpiration lowered rbcS transcript levels in Arabidopsis.
- Taxon
- ArabidopsisArabidopsise0
- Treatment
- experimental reduction of the transpiration rate of a leafe0
- Gene
- rbcSe0
- Outcome
- transcript levels of the small subunit of Rubisco (rbcS) genee0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“experimental reduction of the transpiration rate of a leaf, independent of light, is sufficient to reduce photosynthetic capacity in both species, as well as transcript levels of the small subunit of Rubisco (rbcS) gene in Arabidopsis”
Claim · model-written summary
Shaded tobacco leaves imported less cytokinin than high-light leaves.
- Taxon
- tobaccoNicotiana tabacume1
- Outcome
- cytokinine0
- Direction
- lesse0
- Comparator
- leaves exposed to high lighte0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“shaded leaves import less cytokinin than leaves exposed to high light”
e1“intact, transpiring tobacco plants revealed”
Claim · model-written summary
Reduced transpiration in light was associated with lower cytokinin concentration in Arabidopsis.
- Taxon
- ArabidopsisArabidopsise0
- Treatment
- reduced transpiration rate of a leafe0
- Outcome
- cytokinin concentrations, including the bioactive trans-zeatin and trans-zeatin ribosidee0
- Direction
- lowere0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In Arabidopsis, reduced transpiration rate of a leaf in the light is associated with lower cytokinin concentrations, including the bioactive trans-zeatin and trans-zeatin riboside”
Claim · model-written summary
Reduced transpiration was associated with lower ARR7 and ARR16 expression in Arabidopsis.
- Taxon
- ArabidopsisArabidopsise0
- Treatment
- reduced transpiration rate of a leafe0
- Gene
- ARR7 and ARR16e0
- Outcome
- expression of the cytokinin-responsive genes ARR7 and ARR16e0
- Direction
- reducede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In Arabidopsis, reduced transpiration rate of a leaf in the light is associated with lower cytokinin concentrations, including the bioactive trans-zeatin and trans-zeatin riboside, as well as reduced expression of the cytokinin-responsive genes ARR7 and ARR16”
Claim · model-written summary
External cytokinin application rescued shade effects on rbcS transcript levels in tobacco.
- Taxon
- tobaccoNicotiana tabacume1
- Treatment
- External application of cytokinine0
- Gene
- rbcSe0
- Outcome
- rbcS transcript levelse0
- Direction
- rescuede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“External application of cytokinin to shaded leaves rescued multiple shade effects, including rbcS transcript levels in both species”
e1“tobacco (Nicotiana tabacum)”
Claim · model-written summary
External cytokinin application rescued shade effects on rbcS transcript levels in Arabidopsis.
- Taxon
- ArabidopsisArabidopsise1
- Treatment
- External application of cytokinine0
- Gene
- rbcSe0
- Outcome
- rbcS transcript levelse0
- Direction
- rescuede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“External application of cytokinin to shaded leaves rescued multiple shade effects, including rbcS transcript levels in both species”
e1“Arabidopsis (Arabidopsis thaliana)”
Claim · model-written summary
Induced cytokinin overproduction rescued shade effects on rbcS transcript levels in tobacco.
- Taxon
- tobaccoNicotiana tabacume0
- Treatment
- locally induced cytokinin overproductione0
- Outcome
- rbcS transcript levelse1
- Direction
- rescuede1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“as did locally induced cytokinin overproduction in transgenic tobacco plants”
e1“External application of cytokinin to shaded leaves rescued multiple shade effects, including rbcS transcript levels in both species”
Claim · model-written summary
The authors conclude that reduced xylem import causes lower cytokinin activity in shaded leaves.
- Taxon
- tobaccoNicotiana tabacume1
- Outcome
- cytokinin activity in shaded leavese0
- Direction
- reducede0
- Qualifier
- reduced import through the xyleme0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“light gradients over the foliage of a plant result in reduced cytokinin activity in shaded leaves as a consequence of reduced import through the xylem”
e1“tobacco (Nicotiana tabacum) and Arabidopsis (Arabidopsis thaliana)”
Claim · model-written summary
The authors conclude that cytokinin regulates whole-plant photosynthetic acclimation to canopy light gradients.
- Taxon
- ArabidopsisArabidopsise1
- Outcome
- whole-plant photosynthetic acclimation to light gradients in canopiese0
- Qualifier
- cytokinin is involvede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“cytokinin is involved in the regulation of whole-plant photosynthetic acclimation to light gradients in canopies”
e1“tobacco (Nicotiana tabacum) and Arabidopsis (Arabidopsis thaliana)”
The same questions in other papers
class · molecular: expression · Nicotiana tabacum (tobacco)Positive and negative results
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- negative
- no effect
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See all 27 papers →class · molecular: expression · ArabidopsisPositive and negative results
45 papers in the same direction as this paper · 28 in the opposite direction · 1 reporting no difference from an alternative
- negative
- negative
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See all 75 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.