title: Online CO2 and H2 O oxygen isotope fractionation allows estimation of mesophyll conductance in C4 plants, and reveals that mesophyll conductance decreases as leaves age in both C4 and C3 plants.
abstract: Mesophyll conductance significantly, and variably, limits photosynthesis but we currently have no reliable method of measurement for C4 plants. An online oxygen isotope technique was developed to allow quantification of mesophyll conductance in C4 plants and to provide an alternative estimate in C3 plants. The technique is compared to an established carbon isotope method in three C3 species. Mesophyll conductance of C4 species was similar to that in the C3 species measured, and declined in both C4 and C3 species as leaves aged from fully expanded to senescing. In cotton leaves, simultaneous measurement of carbon and oxygen isotope discrimination allowed the partitioning of total conductance to the chloroplasts into cell wall and plasma membrane versus chloroplast membrane components, if CO2 was assumed to be isotopically equilibrated with cytosolic water, and the partitioning remained stable with leaf age. The oxygen isotope technique allowed estimation of mesophyll conductance in C4 plants and, when combined with well-established carbon isotope techniques, may provide additional information on mesophyll conductance in C3 plants.
authors.affiliation: Faculty of Agriculture and Environment, The University of Sydney, Private Bag 4011, Narellan, NSW, 2567, Australia.
authors.forename: Margaret M
authors.initials: MM
authors.lastname: Barbour
authors.affiliation: Research School of Biology, The Australian National University, Acton, ACT, 0200, Australia.
authors.forename: John R
authors.initials: JR
authors.lastname: Evans
authors.affiliation: Department of Biology, San Francisco State University, San Francisco, CA, 94132, USA.
authors.forename: Kevin A
authors.initials: KA
authors.lastname: Simonin
authors.affiliation: Research School of Biology, The Australian National University, Acton, ACT, 0200, Australia.
authors.forename: Susanne
authors.initials: S
authors.lastname: von Caemmerer
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism*; D002247:Carbon Isotopes; D005591:Chemical Fractionation / Q000379:methods*; D002736:Chloroplasts / Q000378:metabolism; D058503:Mesophyll Cells / Q000378:metabolism*; D009862:Online Systems; D010100:Oxygen / Q000378:metabolism*; D010103:Oxygen Isotopes; D010788:Photosynthesis; D018515:Plant Leaves / Q000033:anatomy & histology / Q000378:metabolism*; D054046:Plant Stomata / Q000502:physiology; D010944:Plants / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; D010103:Oxygen Isotopes; D002245:Carbon Dioxide; D010100:Oxygen
keywords: Flaveria bidentis; Gossypium hirsutum; Nicotiana tabacum; Setaria viridis; Triticum aestivum; Zea mays; mesophyll conductance; oxygen isotope