title: Compound-specific differences in (13)C of soluble carbohydrates in leaves and phloem of 6-month-old Eucalyptus globulus (Labill).
abstract: Movement of photoassimilates from leaves to phloem is an important step for the flux of carbon through plants. Fractionation of carbon isotopes during this process may influence their abundance in heterotrophic tissues. We subjected Eucalyptus globulus to 20, 25 and 28 °C ambient growth temperatures and measured compound-specific δ(13)C of carbohydrates obtained from leaves and bled phloem sap. We compared δ(13)C of sucrose and raffinose obtained from leaf or phloem and of total leaf soluble carbon, with modelled values predicted by leaf gas exchange. Changes in δ(13)C of sucrose and raffinose obtained from either leaves or phloem sap were more tightly coupled to changes in c(i)/c(a) than was δ(13)C of leaf soluble carbon. At 25 and 28 °C, sucrose and raffinose were enriched in (13)C compared to leaf soluble carbon and predicted values - irrespective of tissue type. Phloem sucrose was depleted and raffinose enriched in (13)C compared to leaf extracts. Intermolecular and tissue-specific δ(13)C reveal that multiple systematic factors influence (13)C composition during export to phloem. Predicting sensitivity of these factors to changes in plant physiological status will improve our ability to infer plant function at a range of temporal and spatial scales.
authors.affiliation: Faculty of Agriculture, Food and Natural Resources, The University of Sydney, Sydney 2006, Australia. andrew.merchant@sydney.edu.au
authors.forename: Andrew
authors.initials: A
authors.lastname: Merchant
authors.forename: Birgit
authors.initials: B
authors.lastname: Wild
authors.forename: Andreas
authors.initials: A
authors.lastname: Richter
authors.forename: Sidonie
authors.initials: S
authors.lastname: Bellot
authors.forename: Mark A
authors.initials: MA
authors.lastname: Adams
authors.forename: Erwin
authors.initials: E
authors.lastname: Dreyer
mesh_terms: D001692:Biological Transport; D002247:Carbon Isotopes / Q000032:analysis; D005052:Eucalyptus / Q000502:physiology*; D009928:Organ Specificity / Q000502:physiology; D052585:Phloem / Q000502:physiology*; D010788:Photosynthesis / Q000502:physiology; D018515:Plant Leaves / Q000502:physiology*; D018526:Plant Transpiration / Q000502:physiology; D011887:Raffinose / Q000378:metabolism*; D012995:Solubility; D013395:Sucrose / Q000378:metabolism*; D013696:Temperature
chemical_list: D002247:Carbon Isotopes; D013395:Sucrose; D011887:Raffinose