title: Spatial variation in photosynthetic CO(2) carbon and oxygen isotope discrimination along leaves of the monocot triticale (Triticum × Secale) relates to mesophyll conductance and the Péclet effect.
abstract: Carbon and oxygen isotope discrimination of CO(2) during photosynthesis (Δ(13)C(obs) and Δ(18)O(obs)) were measured along a monocot leaf, triticale (Triticum × Secale). Both Δ(13)C(obs) and Δ(18)O(obs) increased towards the leaf tip. While this was expected for Δ(18)O(obs) , because of progressive enrichment of leaf water associated with the Péclet effect, the result was surprising for Δ(13) C(obs). To explore parameters determining this pattern, we measured activities of key photosynthetic enzymes [ribulose bis-phosphate carboxylase-oxygenase (Rubisco), phosphoenolpyruvate carboxylase (PEPC) and carbonic anhydrase) as well as maximum carboxylation and electron transport rates (V(cmax) and J(max)) along the leaf. Patterns in leaf internal anatomy along the leaf were also quantified. Mesophyll conductance (g(m)) is known to have a strong influence on Δ(13)C(obs) , so we used three commonly used estimation methods to quantify variation in g(m) along the leaf. Variation in Δ(13)C(obs) was correlated with g(m) and chloroplast surface area facing the intercellular air space, but unrelated to photosynthetic enzyme activity. The observed variation could cause errors at higher scales if the appropriate portion of a leaf is not chosen for leaf-level measurements and model parameterization. Our study shows that one-third of the way from the base of the leaf represents the most appropriate portion to enclose in the leaf chamber.
authors.affiliation: Agro-meteorology Division, National Institute for Agro-Environmental Sciences, 3-1-3 Kannondai, Tsukuba, Ibaraki 305-8604, Japan. naomi.kodama@googlemail.com
authors.forename: Naomi
authors.initials: N
authors.lastname: Kodama
authors.forename: Asaph
authors.initials: A
authors.lastname: Cousins
authors.forename: Kevin P
authors.initials: KP
authors.lastname: Tu
authors.forename: Margaret M
authors.initials: MM
authors.lastname: Barbour
mesh_terms: D002244:Carbon / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism*; D002247:Carbon Isotopes / Q000032:analysis; D002734:Chlorophyll / Q000378:metabolism; D002523:Edible Grain / Q000033:anatomy & histology* / Q000201:enzymology / Q000502:physiology*; D004579:Electron Transport; D058503:Mesophyll Cells / Q000502:physiology; D010103:Oxygen Isotopes / Q000032:analysis; D010730:Phosphoenolpyruvate Carboxylase / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology*; D018515:Plant Leaves / Q000033:anatomy & histology / Q000201:enzymology / Q000502:physiology; D018526:Plant Transpiration / Q000502:physiology; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism*; D012434:Secale / Q000502:physiology; D014908:Triticum / Q000502:physiology; D014867:Water / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; D010103:Oxygen Isotopes; D014867:Water; D002734:Chlorophyll; D002245:Carbon Dioxide; D002244:Carbon; D010730:Phosphoenolpyruvate Carboxylase; D012273:Ribulose-Bisphosphate Carboxylase