Exogenous supply of glutamine and active cytokinin to the roots reduces NO3 uptake rates in poplar

Authors

  • PAULINA DLUZNIEWSKA,

    1. Chair of Tree Physiology, Institute of Forest Botany and Tree Physiology, University of Freiburg, Georges-Köhler-Allee 53/54, D-79085 Freiburg, Germany,
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  • ARTHUR GESSLER,

    Corresponding author
    1. Environmental Biology Group, Research School of Biological Sciences, Australian National University, Canberra, ACT, Australia,
    2. Institut National de la Recherche Agronomique (INRA) Centre de Recherche de Nancy, 54280 Champenoux, France,
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  • STANISLAV KOPRIVA,

    1. John Innes Centre, Norwich Research Park, Colney, Norwich NR4 7UH, UK and
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  • MIROSLAV STRNAD,

    1. Laboratory of Growth Regulators, Palacký University & Institute of Experimental Botany AS CR, Šlechtitelü 11, 78371 Olomouc, Czech Republic
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  • ONDŘEJ NOVÁK,

    1. Laboratory of Growth Regulators, Palacký University & Institute of Experimental Botany AS CR, Šlechtitelü 11, 78371 Olomouc, Czech Republic
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  • HENRIETTE DIETRICH,

    1. Chair of Tree Physiology, Institute of Forest Botany and Tree Physiology, University of Freiburg, Georges-Köhler-Allee 53/54, D-79085 Freiburg, Germany,
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  • HEINZ RENNENBERG

    1. Chair of Tree Physiology, Institute of Forest Botany and Tree Physiology, University of Freiburg, Georges-Köhler-Allee 53/54, D-79085 Freiburg, Germany,
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Arthur Gessler. e-mail: arthur.gessler@sonne.uni-freiburg.de

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, γ-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.

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