Contribution of the AMT1;2-mediated apoplastic and AMT1;3-mediated symplastic transport pathway to N partitioning between roots and shoots.

(A and C) Ratio of 15N concentration in shoots to 15N concentration in roots of tko or tko sgn3 without or with reconstituted expression of AMT1;2 (+1;2) or AMT1;3 (+1;3). (B and D) Estimated contribution of the ATP or STP in the absence or presence of an EB at 200 μM (B) or 4 mM 15NH4+ (D). Values were calculated by subtracting the background of tko. All plants were grown hydroponically for 5 weeks in nutrient solution containing 2 mM nitrate, followed by 3 d of N starvation before transfer to 15NH4+ labeling for 1 h. Shoot-to-root 15N concentration ratio was compared when 15NH4+ was supplied at 200 μM (A) or 4 mM concentration (C). Bars represent means ± SD (n = 4 biological replicates). Different letters indicate significant differences according to Tukey’s multiple test at p S1 Data. AMT, ammonium transporter; ATP, apoplastic transport pathway; EB, endodermal bypass; N, nitrogen; 15NH4+, 15N-labeled ammonium; sgn3, schengen 3; STP, symplastic transport pathway; tko, amt1;1amt1;2amt1;3.