title: Phloem sap and leaf delta13C, carbohydrates, and amino acid concentrations in Eucalyptus globulus change systematically according to flooding and water deficit treatment.
abstract: Phloem is a central conduit for the distribution of photoassimilate, nutrients, and signals among plant organs. A revised technique was used to collect phloem sap from small woody plants in order to assess changes in composition induced by water deficit and flooding. Bled phloem sap delta(13)C and sugar concentrations were compared to delta(13)C of bulk material, soluble carbon extracts, and the neutral sugar fraction from leaves. Amino acid composition and inorganic ions of the phloem sap was also analysed. Quantitative, systematic changes were detected in phloem sap composition and delta(13)C in response to altered water availability. Phloem sap delta(13)C was more sensitive to changes of water availability than the delta(13)C of bulk leaf, the soluble carbon fraction, and the neutral soluble fraction of leaves. Changes in water availability also resulted in significant changes in phloem sugar (sucrose and raffinose), inorganic nutrient (potassium), and amino acid (phenylalanine) concentrations with important implications for the maintenance of phloem function and biomass partitioning. The differences in carbohydrate and amino acid composition as well as the delta(13)C in the phloem, along with a new model system for phloem research, offer an improved understanding of the phloem-mediated signal, nutrient, and photoassimilate transduction in relation to water availability.
authors.affiliation: School of Biological, Earth and Environmental Science University of New South Wales, Sydney NSW, Australia 2052. a.merchant@usyd.edu.au
authors.forename: Andrew
authors.initials: A
authors.lastname: Merchant
authors.forename: Andreas D
authors.initials: AD
authors.lastname: Peuke
authors.forename: Claudia
authors.initials: C
authors.lastname: Keitel
authors.forename: Craig
authors.initials: C
authors.lastname: Macfarlane
authors.forename: Charles R
authors.initials: CR
authors.lastname: Warren
authors.forename: Mark A
authors.initials: MA
authors.lastname: Adams
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D002241:Carbohydrates / Q000032:analysis; D002247:Carbon Isotopes / Q000378:metabolism; D005052:Eucalyptus / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant / Q000502:physiology; D052585:Phloem / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D002241:Carbohydrates; D002247:Carbon Isotopes