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JXB Advance Access originally published online on December 18, 2007
Journal of Experimental Botany 2008 59(1):111-119; doi:10.1093/jxb/erm208
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© The Author [2007]. Published by Oxford University Press [on behalf of the Society for Experimental Biology]. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

SPECIAL ISSUE REVIEW PAPER

Amino acids and nitrate as signals for the regulation of nitrogen acquisition

Anthony J. Miller1,*, Xiaorong Fan1,2, Qirong Shen2 and Susan J. Smith1

1Crop Performance and Improvement Division, Rothamsted Research, Harpenden, Herts AL5 2JQ, UK
2College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing 210095, PR China

* To whom correspondence should be addressed. E-mail: tony.miller{at}bbsrc.ac.uk

The uptake of nitrogen (N) by roots is known to change with supply in a manner that suggests that the N status of plants is somehow sensed and can feedback to regulate this process. The most abundant source of N in soils for crops is nitrate. Uptake systems for nitrate, ammonium, and amino acids are present in the roots of most plants including crops. As nitrate is assimilated via conversion to nitrite, then ammonium into amino acids, it has been suggested that the internal pools of amino acids within plants may indicate nitrogen status by providing a signal that can regulate nitrate uptake by the plant. In support of this idea, both nitrate and ammonium influx and transporter transcript were shown to decrease in root tissue treated with exogenously applied amino acids. Several different amino acids have been tested for their effects on influx and transcription and glutamine was most effective. The feedback regulation occurs by changing the expression of transporters, but may also involve the post-translational modification of proteins. For example, some of the cytoplasmic enzymes responsible for nitrate assimilation are regulated by phosphorylation and binding of a 14-3-3 protein. The effects of treating plants with glutamine have been examined, first to identify the uptake of the amino acid and then to measure tissue nitrate reductase activity and cellular pools of nitrate. These results are reviewed in terms of feedback regulation and the putative cell sensing systems for N status including a possible specific role for cytosolic nitrate.

Key words: Amino acids, ammonium uptake, feedback regulation, nitrate uptake, nitrogen sensor

Received 29 March 2007; Revised 9 August 2007 Accepted 9 August 2007


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