Figure 2.

NO₃⁻ influx, NRT2.1, and NAR2.1 mRNA level in roots of wild-type (WT) and transgenic plants in response to 10 mm NH₄NO₃. A to C, Plants were grown in vitro during 8 d on 0.2 mm KNO₃ (white bars) or 10 mm NH₄NO₃ (gray bars) as N source. D to F, WT plants (white bars) and the transgenic line L5 (gray bars) were grown in vitro on 0.2 mm KNO₃ and treated during 4, 6, and 24 h by the addition of 2 mL of a 250 mm NH₄NO₃ solution to reach a final concentration of 10 mm NH₄NO₃. A and D, Root NRT2.1 expression quantified by Q-PCR. Values are means of two biological replicates ± sd. B and E, Root NO₃⁻ influx measured at the external concentration of 0.2 mm ¹⁵NO₃⁻. Values are means of 12 replicates ± sd. C and F, Root NAR2.1 expression quantified by Q-PCR. Values are means of two biological replicates ± sd. Differences between plants on KNO₃ and NH₄NO₃ are significant at *P < 0.05, **P < 0.01, ***P < 0.001 (Student’s t test).