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Record number 536751
Title The energy budget in C4 photosynthesis : insights from a cell-type-specific electron transport model
Author(s) Yin, Xinyou; Struik, Paul C.
Source New Phytologist 218 (2018)3. - ISSN 0028-646X - p. 986 - 998.
DOI http://dx.doi.org/10.1111/nph.15051
Department(s) Crop Physiology
PE&RC
Publication type Refereed Article in a scientific journal
Publication year 2018
Keyword(s) bioenergetics - C modelling - C photosynthesis - cell type - cyclic electron transport - energy balance - mixed decarboxylation - quantum yield
Abstract Extra ATP required in C4 photosynthesis for the CO2-concentrating mechanism probably comes from cyclic electron transport (CET). As metabolic ATP : NADPH requirements in mesophyll (M) and bundle-sheath (BS) cells differ among C4 subtypes, the subtypes may differ in the extent to which CET operates in these cells. We present an analytical model for cell-type-specific CET and linear electron transport. Modelled NADPH and ATP production were compared with requirements. For malic-enzyme (ME) subtypes, c. 50% of electron flux is CET, occurring predominantly in BS cells for standard NADP-ME species, but in a ratio of c. 6 : 4 in BS : M cells for NAD-ME species. Some C4 acids follow a secondary decarboxylation route, which is obligatory, in the form of ‘aspartate-malate’, for the NADP-ME subtype, but facultative, in the form of phosphoenolpyruvate-carboxykinase (PEP-CK), for the NAD-ME subtype. The percentage for secondary decarboxylation is c. 25% and that for 3-phosphoglycerate reduction in BS cells is c. 40%; but these values vary with species. The ‘pure’ PEP-CK type is unrealistic because its is impossible to fulfil ATP : NADPH requirements in BS cells. The standard PEP-CK subtype requires negligible CET, and thus has the highest intrinsic quantum yields and deserves further studies in the context of improving canopy productivity.
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