Physiological functions of the ammonium transporters AMT1;1 and AMT1;3 for ammonium uptake In Arabidopsis roots

摘要

Ammonium and nitrate are the most important nitrogen sources for most plant species in agricultural plant production. In the model plant species Arabidopsis thaliana four ammonium transporter genes have been shown to be expressed in roots and to encode functional transporters when expressed in yeast. This raised the question whether all these transporters are similarly important for primary ammonium uptake in roots. Measuring the influx of ~(15)N-labeled ammonium in T-DNA insertion lines with alacking expression of AMT1;1 and AMT1;3 showed that the loss of either AMT1;1 or AMT1;3 led to a loss of one third of the high-affinity ammonium uptake capacity, when plants were precultured under nitrogen deficiency. Under N-sufficient conditions, however, only AMT1;3 but not AMT1;1 contributed significantly to ammonium influx. The double insertion line amt1;3-1 amt1;1-1 showed up to 70% decrease in ammonium influx relative to both wild-types. In agreement with the localization of AMT-GEP fusion proteins in the rhizodermis and root hairs of Arabidopsis roots, it is suggested that AMT1;1 and AMT1;3 contribute additively to the overall ammonium uptake capacity in Arabidopsis roots under nitrogen deficiency.