title: Exogenous supply of glutamine and active cytokinin to the roots reduces NO3- uptake rates in poplar.
abstract: The present study shows for the first time the influence of exogenously applied amino acids and cytokinin on the physiological and molecular aspects of N metabolism in poplar trees. In a short-term feeding experiment, glutamine or trans-zeatin riboside (tZR) was added directly to the nutrient solution. NO3- net uptake declined significantly in response to both treatments. Feeding with glutamine brought about an increase in concentrations of different amino compounds in the roots (glutamine, glutamate, alanine, gamma-amino butyric acid (GABA) and NH4+, which negatively correlated with the net NO3- uptake. The plants showed a reduction of cytosolic glutamine synthetase 1 (GS1) transcript level in the roots. In addition, glutamine feeding changed the root-to-shoot distribution on N assimilation in favour of the leaves and plant internal N cycling. tZR treatment resulted in expansion of zeatin-type (Z-type) cytokinins in the roots and increased nitrate reductase (NR)-mRNA level. The results indicate that both particular amino acids and active cytokinins are involved in the feedback regulation of N uptake and metabolism in poplar. We propose that inhibition of N uptake by cytokinins in poplar is more complex than that mediated by amino compounds, and other effectors are involved in this regulation.
authors.affiliation: Chair of Tree Physiology, Institute of Forest Botany and Tree Physiology, University of Freiburg, Georges-Köhler-Allee 53/ 54, D-79085 Freiburg, Germany.
authors.forename: Paulina
authors.initials: P
authors.lastname: Dluzniewska
authors.forename: Arthur
authors.initials: A
authors.lastname: Gessler
authors.forename: Stanislav
authors.initials: S
authors.lastname: Kopriva
authors.forename: Miroslav
authors.initials: M
authors.lastname: Strnad
authors.forename: Ondrej
authors.initials: O
authors.lastname: Novák
authors.forename: Henriette
authors.initials: H
authors.lastname: Dietrich
authors.forename: Heinz
authors.initials: H
authors.lastname: Rennenberg
mesh_terms: D003583:Cytokinins / Q000494:pharmacology*; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism; D005973:Glutamine / Q000494:pharmacology*; D050901:Nitrate Reductase / Q000378:metabolism; D009566:Nitrates / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects*; D032107:Populus / Q000187:drug effects* / Q000378:metabolism*; D013997:Time Factors; D052584:Xylem / Q000378:metabolism
chemical_list: D003583:Cytokinins; D009566:Nitrates; D005973:Glutamine; D050901:Nitrate Reductase; C081173:glutamine synthetase I; D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen