Increased proline loading to phloem and its effects on nitrogen uptake and assimilation in water-stressed white clover (Trifolium repens)

Authors

  • Bok-Rye Lee,

    1. Department of Animal Science, Institute of Agricultural Science and Technology, Environment-Friendly Agriculture Research Center (EFARC), College of Agriculture & Life Science, Chonnam National University, Buk-Gwangju PO Box 205, Gwangju, 500-600, Korea
    2. Present address: Department of Metabolic Biology, John Innes Centre, Norwich Research Park, Colney, Norwich NR4 7UH, UK
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  • Yu Lan Jin,

    1. College of Chemistry and Pharmacy, Qingdao Agriculture University, Qingdao City, Shandong, China
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  • Jean-Christophe Avice,

    1. INRA, UMR INRA-UCBN, Écophysiologie Végétale, Agronomie et Nutritions NCS, Institut de Biologie Fondamentale et Appliquée, IFR 146 ICORE, Université de Caen, F-14032 Caen Cedex, France
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  • Jean-Bernard Cliquet,

    1. INRA, UMR INRA-UCBN, Écophysiologie Végétale, Agronomie et Nutritions NCS, Institut de Biologie Fondamentale et Appliquée, IFR 146 ICORE, Université de Caen, F-14032 Caen Cedex, France
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  • Alain Ourry,

    1. INRA, UMR INRA-UCBN, Écophysiologie Végétale, Agronomie et Nutritions NCS, Institut de Biologie Fondamentale et Appliquée, IFR 146 ICORE, Université de Caen, F-14032 Caen Cedex, France
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  • Tae-Hwan Kim

    1. Department of Animal Science, Institute of Agricultural Science and Technology, Environment-Friendly Agriculture Research Center (EFARC), College of Agriculture & Life Science, Chonnam National University, Buk-Gwangju PO Box 205, Gwangju, 500-600, Korea
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Author for correspondence:
Tae-Hwan Kim
Tel:+82-62-530-2126
Email: grassl@chonnam.ac.kr

Summary

  • • The aim of this study was to investigate the physiological significance of increased proline loading to phloem caused by water-deficit stress in relation to nitrogen (N) uptake and assimilation.
  • • N uptake and N assimilation were quantified by 15N tracing in well-watered (control) and water deficit-stressed white clover (Trifolium repens). De novo proline synthesis and proline loading to the phloem were also compared between treatments. The relationships among proline concentrations in phloem exudates, N uptake, and assimilation of newly absorbed N were assessed.
  • • The newly synthesized proline in the phloem exudates increased rapidly after 3 d of water deficit. The water-deficit treatment significantly reduced the maximum nitrate reductase activity (NRA), and also attenuated de novo synthesis of amino acids and proteins in the roots. The increase in proline concentrations in phloem exudates was closely related to reductions in NRA in the roots, N uptake, and the assimilation of newly absorbed N. The accumulation of proline induced in roots by exogenous proline and NH4Cl treatments was closely associated with the decrease in NRA.
  • • These results indicate that increased proline transport to roots via phloem caused by water deficit has a significant influence on the down-regulation of N uptake and the assimilation of newly absorbed N.

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