title: Simple generalisation of a mesophyll resistance model for various intracellular arrangements of chloroplasts and mitochondria in C3leaves.
abstract: The classical definition of mesophyll conductance (gm) represents an apparent parameter (gm,app) as it places (photo)respired CO2at the same compartment where the carboxylation by Rubisco takes place. Recently, Tholen and co-workers developed a framework, in which gmbetter describes a physical diffusional parameter (gm,dif). They partitioned mesophyll resistance (rm,dif= 1/gm,dif) into two components, cell wall and plasmalemma resistance (rwp) and chloroplast resistance (rch), and showed that gm,appis sensitive to the ratio of photorespiratory (F) and respiratory (Rd) CO2release to net CO2uptake (A): gm,app= gm,dif/[1 + ω(F + Rd)/A], where ω is the fraction of rchin rm,dif. We herein extend the framework further by considering various scenarios for the intracellular arrangement of chloroplasts and mitochondria. We show that the formula of Tholen et al. implies either that mitochondria, where (photo)respired CO2is released, locate between the plasmalemma and the chloroplast continuum or that CO2in the cytosol is completely mixed. However, the model of Tholen et al. is still valid if ω is replaced by ω(1-σ), where σ is the fraction of (photo)respired CO2that experiences rch(in addition to rwpand stomatal resistance) if this CO2is to escape from being refixed. Therefore, responses of gm,appto (F + Rd)/A lie somewhere between no sensitivity in the classical method (σ =1) and high sensitivity in the model of Tholen et al. (σ =0).
authors.affiliation: Centre for Crop Systems Analysis, Wageningen University & Research, P.O. Box 430, 6700 AK, Wageningen, The Netherlands. Xinyou.yin@wur.nl.
authors.forename: Xinyou
authors.identifier: http://orcid.org/0000-0001-8273-8022
authors.initials: X
authors.lastname: Yin
authors.affiliation: Centre for Crop Systems Analysis, Wageningen University & Research, P.O. Box 430, 6700 AK, Wageningen, The Netherlands.
authors.forename: Paul C
authors.initials: PC
authors.lastname: Struik
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism*; D058503:Mesophyll Cells / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D008954:Models, Biological; D010788:Photosynthesis / Q000502:physiology; D018515:Plant Leaves / Q000378:metabolism*
chemical_list: D002245:Carbon Dioxide
keywords: CO2 transfer; Internal conductance; Mesophyll resistance