Abstract
The C4 photosynthesis carbon-concentrating mechanism in maize (Zea mays) has two CO2 delivery pathways to the bundle sheath (BS; via malate or aspartate), and rates of phosphoglyceric acid reduction, starch synthesis, and phosphoenolpyruvate regeneration also vary between BS and mesophyll (M) cells. The theoretical partitioning of ATP supply between M and BS cells was derived for these metabolic activities from simulated profiles of light penetration across a leaf, with a potential 3-fold difference in the fraction of ATP produced in the BS relative to M (from 0.29 to 0.96). A steady-state metabolic model was tested using varying light quality to differentially stimulate M or BS photosystems. CO2 uptake, ATP production rate (JATP; derived with a low oxygen/chlorophyll fluorescence method), and carbon isotope discrimination were measured on plants under a low light intensity, which is considered to affect C4 operating efficiency. The light quality treatments did not change the empirical ATP cost of gross CO2 assimilation (JATP/GA). Using the metabolic model, measured JATP/GA was compared with the predicted ATP demand as metabolic functions were varied between M and BS. Transamination and the two decarboxylase systems (NADP-malic enzyme and phosphoenolpyruvate carboxykinase) were critical for matching ATP and reduced NADP demand in BS and M when light capture was varied under contrasting light qualities.
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Claims 3
Claim · model-written summary
Simulated light penetration profiles across a maize leaf gave a potential 3-fold difference in the fraction of ATP produced in bundle sheath relative to mesophyll cells, from 0.29 to 0.96.
- Outcome
- fraction of ATP produced in the BS relative to Me1
- Value
- from 0.29 to 0.96e1
- Qualifier
- 3-fold differencee1
Zea maysOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“maize (Zea mays)”
e1“with a potential 3-fold difference in the fraction of ATP produced in the BS relative to M (from 0.29 to 0.96)”
Claim · model-written summary
Light quality treatments did not change the empirical ATP cost of gross CO2 assimilation (JATP/GA) in maize.
- Treatment
- light quality treatmentse1
- Outcome
- empirical ATP cost of gross CO2 assimilation (JATP/GA)e1
- Direction
- did not changee1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“maize (Zea mays)”
e1“The light quality treatments did not change the empirical ATP cost of gross CO2 assimilation (JATP/GA)”
Claim · model-written summary
Transamination and the two decarboxylase systems (NADP-malic enzyme and phosphoenolpyruvate carboxykinase) were critical for matching ATP and reduced NADP demand in bundle sheath and mesophyll cells under contrasting light qualities.
- Treatment
- contrasting light qualitiese1
- Gene
- NADP-malic enzyme and phosphoenolpyruvate carboxykinasee1
- Outcome
- matching ATP and reduced NADP demand in BS and Me1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“maize (Zea mays)”
e1“Transamination and the two decarboxylase systems (NADP-malic enzyme and phosphoenolpyruvate carboxykinase) were critical for matching ATP and reduced NADP demand in BS and M when light capture was varied under contrasting light qualities”
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