title: A generalized stoichiometric model of C3, C2, C2+C4, and C4 photosynthetic metabolism.
abstract: The goal of suppressing photorespiration in crops to maximize assimilation and yield is stimulating considerable interest among researchers looking to bioengineer carbon-concentrating mechanisms into C3plants. However, detailed quantification of the biochemical activities in the bundle sheath is lacking. This work presents a general stoichiometric model for C3, C2, C2+C4, and C4assimilation (SMA) in which energetics, metabolite traffic, and the different decarboxylating enzymes (NAD-dependent malic enzyme, NADP-dependent malic enzyme, or phosphoenolpyruvate carboxykinase) are explicitly included. The SMA can be used to refine experimental data analysis or formulate hypothetical scenarios, and is coded in a freely available Microsoft Excel workbook. The theoretical underpinnings and general model behaviour are analysed with a range of simulations, including (i) an analysis of C3, C2, C2+C4, and C4in operational conditions; (ii) manipulating photorespiration in a C3plant; (iii) progressively upregulating a C2shuttle in C3photosynthesis; (iv) progressively upregulating a C4cycle in C2photosynthesis; and (v) manipulating processes that are hypothesized to respond to transient environmental inputs. Results quantify the functional trade-offs, such as the electron transport needed to meet ATP/NADPH demand, as well as metabolite traffic, inherent to different subtypes. The SMA refines our understanding of the stoichiometry of photosynthesis, which is of paramount importance for basic and applied research.
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Sheffield, S10 2TN, UK c.bellasio@sheffield.ac.uk.
authors.forename: Chandra
authors.identifier: 0000-0002-3865-7521
authors.initials: C
authors.lastname: Bellasio
mesh_terms: D003198:Computer Simulation; D008954:Models, Biological; D008956:Models, Chemical; D010788:Photosynthesis
keywords: Assimilation; NAD-ME; NADP-ME; PEPCK.; bioengineering; carbon-concentrating mechanism; constraint; dark reactions; flux balance; flux-balance analysis