Abstract
BACKGROUND AND AIMS: Sink-source imbalance could cause an accumulation of total non-structural carbohydrates (TNC; soluble sugar and starch) in source leaves. We aimed to clarify interspecific differences in how sink-source imbalance and TNC causes the downregulation of photosynthesis among three legume plants. The TNC in source leaves was altered by short-term manipulative treatments, and its effects on photosynthetic characteristics were evaluated. METHODS: Soybean, French bean and azuki bean were grown under high nitrogen availability. After primary leaves were fully expanded, they were subjected to additional treatments: defoliation except for two primary leaves; transfer to low nitrogen conditions; transfer to low nitrogen conditions and defoliation; or irradiation by light-emitting diodes. Physiological and anatomical traits such as TNC content, maximum photosynthetic rate, cell wall content and δ13C values of primary leaves and whole-plant growth were examined. KEY RESULTS: Among the three legume plants, the downregulation of maximum photosynthesis and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) content was co-ordinated with an increase in TNC only in French bean. Rubisco did not decrease with an increase in TNC in soybean and azuki bean. The defoliation treatment caused an increase in cell wall content especially in soybean, and maximum photosynthesis decreased despite resulting in a higher Rubisco content. This indicates that a decrease in mesophyll conductance could cause photosynthetic downregulation, which was confirmed by an increase in δ13C. CONCLUSION: The present results suggest that a downregulation of photosynthesis in response to increased levels of TNC in source leaves can result not only from decreases in Rubisco content, but also from anatomical factors, such as an increase in cell wall thickness leading to reduced chloroplast CO2 concentrations.
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Claims 7
Claim · model-written summary
In French bean only, downregulation of maximum photosynthesis co-ordinated with an increase in TNC.
- Taxon
- French bean
Phaseolus vulgarise0 - Compound
- TNCe0
- Outcome
- maximum photosynthesise0
- Direction
- downregulatione0
- Qualifier
- only in French beane0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Among the three legume plants, the downregulation of maximum photosynthesis and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) content was co-ordinated with an increase in TNC only in French bean”
Claim · model-written summary
In soybean, Rubisco content did not decrease with an increase in TNC.
- Taxon
- soybean
Glycine maxe1 - Compound
- TNCe1
- Outcome
- Rubiscoe1
- Direction
- did not decreasee1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“Rubisco did not decrease with an increase in TNC in soybean and azuki bean”
Claim · model-written summary
In azuki bean, Rubisco content did not decrease with an increase in TNC.
- Taxon
- azuki bean
Vigna angularise1 - Compound
- TNCe1
- Outcome
- Rubiscoe1
- Direction
- did not decreasee1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“Rubisco did not decrease with an increase in TNC in soybean and azuki bean”
Claim · model-written summary
Defoliation increased cell wall content, especially in soybean.
- Taxon
- soybeanGlycine maxe2
- Treatment
- defoliatione2
- Outcome
- cell wall contente2
- Direction
- increasee2
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e2“The defoliation treatment caused an increase in cell wall content especially in soybean, and maximum photosynthesis decreased despite resulting in a higher Rubisco content”
Claim · model-written summary
Defoliation decreased maximum photosynthesis in soybean despite a higher Rubisco content.
- Taxon
- soybeanGlycine maxe2
- Treatment
- defoliatione2
- Outcome
- maximum photosynthesise2
- Direction
- decreasede2
- Qualifier
- despite resulting in a higher Rubisco contente2
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e2“The defoliation treatment caused an increase in cell wall content especially in soybean, and maximum photosynthesis decreased despite resulting in a higher Rubisco content”
Claim · model-written summary
A decrease in mesophyll conductance is proposed to cause photosynthetic downregulation in soybean, supported by a rise in delta13C.
- Taxon
- soybeanGlycine maxe2
- Outcome
- photosynthetic downregulatione3
- Qualifier
- decrease in mesophyll conductancee3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e2“The defoliation treatment caused an increase in cell wall content especially in soybean, and maximum photosynthesis decreased despite resulting in a higher Rubisco content”
e3“This indicates that a decrease in mesophyll conductance could cause photosynthetic downregulation, which was confirmed by an increase in δ13C”
Claim · model-written summary
Photosynthetic downregulation under high TNC in source leaves may result from anatomical factors as well as lower Rubisco content.
Verbatim
e0“Among the three legume plants, the downregulation of maximum photosynthesis and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) content was co-ordinated with an increase in TNC only in French bean”
e4“a downregulation of photosynthesis in response to increased levels of TNC in source leaves can result not only from decreases in Rubisco content, but also from anatomical factors”