Estimating Mesophyll Conductance from Measurements of C18OO Photosynthetic Discrimination and Carbonic Anhydrase Activity. Issue 2 (13th August 2018)

• Record Type: Journal Article
• Authors: Ogée, Jérôme; Wingate, Lisa; Genty, Bernard
• Is Part Of: Plant physiology. Volume 178:Issue 2(2018)
• Page Start: 728
• Page End: 752
• Publication Date: 2018-08-13
• Subjects: Plant physiology -- Periodicals; Botany -- Periodicals; Periodicals; Electronic journals; 571.2
• DOI: 10.1104/pp.17.01031
• Languages: English
• ISSNs: 0032-0889

Abstract

Abstract : A new model based on the relationship between C 18 OO photosynthetic discrimination and carbonic anhydrase activity estimates mesophyll conductance in C3 and C4 plants. Abstract: Carbonic anhydrase (CA) activity in leaves catalyzes the 18 O exchange between CO2 and water during photosynthesis. This feature has been used to estimate the mesophyll conductance to CO2 ( g m ) from measurements of online C 18 OO photosynthetic discrimination (∆ 18 O). Based on CA assays on leaf extracts, it has been argued that CO2 in mesophyll cells should be in isotopic equilibrium with water in most C3 species as well as many C4 dicot species. However, this seems incompatible with ∆ 18 O data that would indicate a much lower degree of equilibration, especially in C4 plants under high light intensity. This apparent contradiction is resolved here using a new model of C3 and C4 photosynthetic discrimination that includes competition between CO2 hydration and carboxylation and the contribution of respiratory fluxes. This new modeling framework is used to revisit previously published data sets on C3 and C4 species, including CA-deficient plants. We conclude that (1) newly ∆ 18 O-derived g m values are usually close but significantly higher (typically 20% and up to 50%) than those derived assuming full equilibration and (2) despite the uncertainty associated with the respiration rate in light, or the water isotope gradient between mesophyll and bundle sheath cells, robust estimates of ∆ 18 O-derived g m can be achieved in both C3 and C4 plants.