Role of AtAMT1;2 in nitrogen uptake and plant growth.

Abstract

In Arabidopsis, six ammonium transporters mediate the movement of ammonium in or out of cells. Uncertainty exists about their individual location and role, either in primary ammonium uptake or in intercellular translocation of ammonium. Using the endogenous AMT1;2 promoter to drive an AMT1;2:GFP fusion construct, it was shown that AMT1;2 is primarily localised to root endodermal and cortical cells, while in shoots natural fluorescence in the leaves prevented definitive localisation in cells and internal organelles (e.g. chloroplasts). A growth analysis of amt1;2 and its corresponding wild type parental line revealed improved growth of an amt1;2 TDNA insertion line in media containing 2 mM KNO3. No difference in growth was observed in media containing 1 mM NH4NO3. Using 15N to measure net NH4 + and NO3 - uptake suggested the growth response in the amt1;2 line was not a result of improved nitrogen uptake. Furthermore, examination of high affinity ammonium transport in the amt1;2 and WT lines revealed no detectable difference in ammonium uptake in either N-starved or N-sufficient grown plants respectively.