title: The efficiency of the CO2-concentrating mechanism during single-cell C4 photosynthesis.
abstract: The photosynthetic efficiency of the CO(2)-concentrating mechanism in two forms of single-cell C(4) photosynthesis in the family Chenopodiaceae was characterized. The Bienertioid-type single-cell C(4) uses peripheral and central cytoplasmic compartments (Bienertia sinuspersici), while the Borszczowioid single-cell C(4) uses distal and proximal compartments of the cell (Suaeda aralocaspica). C(4) photosynthesis within a single-cell raises questions about the efficiency of this type of CO(2) -concentrating mechanism compared with the Kranz-type. We used measurements of leaf CO(2) isotope exchange (Δ(13) C) to compare the efficiency of the single-cell and Kranz-type forms of C(4) photosynthesis under various temperature and light conditions. Comparisons were made between the single-cell C(4) and a sister Kranz form, S. eltonica[NAD malic enzyme (NAD ME) type], and with Flaveria bidentis[NADP malic enzyme (NADP-ME) type with Kranz Atriplicoid anatomy]. There were similar levels of Δ(13) C discrimination and CO(2) leakiness (Φ) in the single-cell species compared with the Kranz-type. Increasing leaf temperature (25 to 30 °C) and light intensity caused a decrease in Δ(13) C and Φ across all C(4) types. Notably, B. sinuspersici had higher Δ(13) C and Φ than S. aralocaspica under lower light. These results demonstrate that rates of photosynthesis and efficiency of the CO(2) -concentrating mechanisms in single-cell C(4) plants are similar to those in Kranz-type.
authors.affiliation: School of Biological Sciences, Washington State University, Pullman, WA 99164-4236, USA.
authors.forename: Jenny L
authors.initials: JL
authors.lastname: King
authors.forename: Gerald E
authors.initials: GE
authors.lastname: Edwards
authors.forename: Asaph B
authors.initials: AB
authors.lastname: Cousins
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism*; D002247:Carbon Isotopes / Q000032:analysis; D019663:Chenopodiaceae / Q000166:cytology / Q000502:physiology* / Q000528:radiation effects; D008027:Light; D008291:Malate Dehydrogenase / Q000378:metabolism; D010788:Photosynthesis; D059828:Plant Cells / Q000502:physiology / Q000528:radiation effects; D018515:Plant Leaves / Q000166:cytology / Q000502:physiology / Q000528:radiation effects; D013696:Temperature
chemical_list: D002247:Carbon Isotopes; D002245:Carbon Dioxide; D008291:Malate Dehydrogenase