The Operation of Two Decarboxylases Transamination and Partitioning of C4 Metabolic Processes between Mesophyll and Bundle Sheath Cells Allows Light Capture To Be Balanced for the Maize C4 Pathway

摘要

The C4 photosynthesis carbon-concentrating mechanism in maize (Zea mays) has two CO2 delivery pathways to the bundle sheath (; via malate or aspartate), and rates of phosphoglyceric acid reduction, starch synthesis, and phosphoenolpyruvate regeneration also vary between and mesophyll () cells. The theoretical partitioning of ATP supply between and 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 relative to (from 0.29 to 0.96). A steady-state metabolic model was tested using varying light quality to differentially stimulate or photosystems. CO2 uptake, ATP production rate (; 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 (/). Using the metabolic model, measured / was compared with the predicted ATP demand as metabolic functions were varied between and . Transamination and the two decarboxylase systems (NADP-malic enzyme and phosphoenolpyruvate carboxykinase) were critical for matching ATP and reduced NADP demand in href="#def2" rid="def2" class=" def">BS and href="#def3" rid="def3" class=" def">M when light capture was varied under contrasting light qualities.