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  • 1.
    Husted, Sören
    et al.
    Plant Nutrition Laboratory, Roy. Vet./Agricultural University, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Copenhagen, Denmark.
    Mattsson, Marie
    Plant Nutrition Laboratory, Roy. Vet./Agricultural University, Copenhagen, Denmark.
    Möllers, Christian
    Plant Nutrition Laboratory, Roy. Vet./Agricultural University, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Copenhagen, Denmark.
    Wallbraun, Michael
    Institute of Agronomy and Plant Breeding, University of Göttingen, von Siebold Strasse 8, D-37075 Göttingen, Germany.
    Schjoerring, Jan K.
    Plant Nutrition Laboratory, Roy. Vet./Agricultural University, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Copenhagen, Denmark.
    Photorespiratory NH4+ Production in Leaves of Wild-Type and Glutamine Synthetase 2 Antisense Oilseed Rape2002In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 130, no 2, p. 989-998Article in journal (Refereed)
    Abstract [en]

    Exposure of oilseed rape (Brassica napus) plants to increasing leaf temperatures between 15°C and 25°C increased photorespiratory NH4+ production from 0.7 to 3.5 µmol m-2 s-1. Despite the 5-fold increase in the rate of NH4+ production, the NH4+ concentration in root and leaf tissue water and xylem sap dropped significantly, whereas that in the leaf apoplastic fluid remained constant. The in vitro activity of glutamine synthetase (GS) in both leaves and roots also increased with temperature and in all cases substantially exceeded the observed rates of photorespiratory NH4+ production. The surplus of GS in oilseed rape plants was confirmed using GS2 antisense plants with 50% to 75% lower in vitro leaf GS activity than in the wild type. Despite the substantial reduction in GS activity, there was no tendency for antisense plants to have higher tissue NH4+ concentrations than wild-type plants and no overall correlation between GS activity and tissue NH4+ concentration was observed. Antisense plants exposed to leaf temperatures increasing from 14°C to 27°C or to a trifold increase in the O2 to CO2 ratio did not show any change in steady-state leaf tissue NH4+ concentration or in NH3 emission to the atmosphere. The antisense plants also had similar leaf tissue concentrations of glutamine, glycine, and serine as the wild type, whereas glutamate increased by 38%. It is concluded that photorespiration does not control tissue or apoplastic levels of NH4+ in oilseed rape leaves and, as a consequence, that photorespiration does not exert a direct control on leaf atmosphere NH3 fluxes.

  • 2.
    Mattsson, Marie
    et al.
    Plant Nutrition Laboratory, Department of Agricultural Sciences, Royal Vet. and Agricultural Univ., Frederiksberg C, Copenhagen, Denmark.
    Schjørring, Jan K.
    Plant Nutrition Laboratory, Department of Agricultural Sciences, Royal Vet. and Agricultural Univ., Thorvaldensvej 40, DK-1871 Frederiksberg C, Copenhagen, Denmark.
    Dynamic and steady-state responses of inorganic nitrogen pools and NH3 exchange in leaves of Lolium perenne and Bromus erectus to changes in root nitrogen supply2002In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 128, no 2, p. 742-750Article in journal (Refereed)
    Abstract [en]

    Short- and long-term responses of inorganic N pools and plant-atmosphere NH3 exchange to changes in external N supply were investigated in 11-week-old plants of two grass species, Lolium perenne and Bromus erectus, characteristic of N-rich and N-poor grassland ecosystems, respectively. A switch of root N source from NO3- to NH4+ caused within 3 h a 3- to 6-fold increase in leaf apoplastic NH4+ concentration and a simultaneous decrease in apoplastic pH of about 0.4 pH units in both species. The concentration of total extractable leaf tissue NH4+ also increased two to three times within 3 h after the switch. Removal of exogenous NH4+ caused the apoplastic NH4+ concentration to decline back to the original level within 24 h, whereas the leaf tissue NH4+concentration decreased more slowly and did not reach the original level in 48 h. After growing for 5 weeks with a steady-state supply of NO3- or NH4+, L. perenne were in all cases larger, contained more N, and utilized the absorbed N more efficiently for growth than B. erectus, whereas the two species behaved oppositely with respect to tissue concentrations of NO3-, NH4+, and total N. Ammonia compensation points were higher for B. erectus than for L. perenne and were in both species higher for NH4+- than for NO3--grown plants. Steady-state levels of apoplastic NH4+, tissue NH4+, and NH3 emission were significantly correlated. It is concluded that leaf apoplastic NH4+ is a highly dynamic pool, closely reflecting changes in the external N supply. This rapid response may constitute a signaling system coordinating leaf N metabolism with the actual N uptake by the roots and the external N availability.

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