title: Allocation of reserve-derived and currently assimilated carbon and nitrogen in seedlings of Helianthus annuus under sub-ambient and elevated CO growth conditions.
abstract: Here, we analysed the transition from heterotrophic to autotrophic growth of the epigeal species sunflower (Helianthus annuus), and how transition is affected by CO(2). Growth analysis and steady-state (13)CO(2)/(12)CO(2) and (15)NO(3) (-)/(14)NO(3) (-) labelling were used to quantify reserve- and current assimilation-derived carbon (C) and nitrogen (N) allocation to shoots and roots in the presence of 200 and 1,000 micromol CO(2) mol(-1) air. Growth was not influenced by CO(2) until cotyledons unfolded. Then, C accumulation at elevated CO(2) increased to a rate 2-2.5 times higher than in sub-ambient CO(2) due to increased unit leaf rate (+120%) and leaf expansion (+60%). CO(2) had no effect on mobilization and allocation of reserve-derived C and N, even during the transition period. Export of autotrophic C from cotyledons began immediately following the onset of photosynthetic activity, serving roots and shoots near-simultaneously. Allocation of autotrophic C to shoots was increased at sub-ambient CO(2). The synchrony in transition from heterotrophic to autotrophic supply for different sinks in sunflower contrasts with the sequential transition reported for species with hypogeal germination.
authors.affiliation: Lehrstuhl für Grünlandlehre, Technische Universität München, Am Hochanger 1, D-85350 Freising, Germany.
authors.forename: Christoph A
authors.initials: CA
authors.lastname: Lehmeier
authors.forename: Rudi
authors.initials: R
authors.lastname: Schäufele
authors.forename: Hans
authors.initials: H
authors.lastname: Schnyder
mesh_terms: D002244:Carbon / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism*; D018548:Cotyledon / Q000502:physiology; D006368:Helianthus / Q000502:physiology*; D009584:Nitrogen / Q000378:metabolism*; D018517:Plant Roots / Q000254:growth & development; D036226:Seedlings / Q000254:growth & development / Q000502:physiology*
chemical_list: D002245:Carbon Dioxide; D002244:Carbon; D009584:Nitrogen