15[N]-urea influx in Arabidopsis plants. Urea uptake into roots was determined using 6-weeks-old plants of wild type Col-0 (WT), atdur3-3 mutant line and three ZmDUR3
-transformed lines (atdur3-3 + ZmDUR3-A, -B, -C) grown in a complete nutrient solution containing nitrogen as 1 mM ammonium nitrate. 4 days before the experiment, plants were transferred to N-free medium. For the assay, 100 μM 15[N]-urea was supplied to the medium for 15 min. Data are mean ±SD of three independent experiments and different letters above the bars indicate statistically significant differences (ANOVA, Student-Newman-Keuls, P < 0.05, n=3).