JXB Advance Access published online on July 4, 2006
Journal of Experimental Botany, doi:10.1093/jxb/erl028
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1 Umeå Plant Science Center, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, S-90183, Umeå, Sweden; Present address: Royal Veterinary and Agricultural University, Department of Plant Biology, DK-1871 Frederiksberg C, Denmark
* To whom correspondence should be addressed. Although an increasing number of studies show that many plant species have the capacity to take up amino acids from exogenous sources, the importance of such uptake for plant nitrogen nutrition is largely unknown. Moreover, little is known regarding metabolism and distribution of amino acid-N following uptake or of the regulation of these processes in response to plant nitrogen status. Here results are presented from a study following uptake, metabolism, and distribution of nitrogen from NO3-, NH4+, Glu, or Ala in Scots pine (Pinus sylvestris L). In a parallel experiment, Ala uptake, processing, and shoot allocation were also monitored following a range of pretreatments intended to alter plant C- and N-status. Uptake data, metabolite profiles, N fluxes through metabolite pools and tissues, as well as alanine aminotransferase activity are presented. The results show that uptake of the organic N sources was equal to or larger than NH4+ uptake, while NO3- uptake was comparatively low. Down-regulation of Ala uptake in response to pretreatments with NH4NO3 or methionine sulphoximine (MSX) indicates similarities between amino acid and inorganic N uptake regulation. N derived from amino acid uptake exhibited a rapid flux through the amino acid pool following uptake. Relative shoot allocation of amino acid-N was equal to that of NH4+, but smaller than for NO3-. Increased N status as well as MSX treatment significantly increased relative shoot allocation of Ala-N suggesting that NH4+ may have a role in the regulation of shoot allocation of amino acid-N.
Received September 6, 2005
Accepted April 17, 2006
RESEARCH PAPER
Uptake, metabolism and distribution of organic and inorganic nitrogen sources by Pinus sylvestris
Jörgen Persson 1,
Per Gardeström 2,
and
Torgny Näsholm 3 *
2 Umeå Plant Science Center, Department of Plant Physiology, Umeå University, S-90183, Umeå, Sweden
3 Umeå Plant Science Center, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, S-90183, Umeå, Sweden
Torgny Näsholm, E-mail: torgny.nasholm{at}genfys.slu.se
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