Figure 5.

¹³NO₃⁻ influx into wild-type and Atnrt3.1-2 mutant roots. A, High-affinity ¹³NO₃⁻ influx. Plants were grown for 4 weeks in 1 mm NH₄NO₃ and then nitrogen deprived for 1 week before being reexposed to 1 mm KNO₃ for 6 h. Nitrate influx was then measured at 10, 25, 50, 75, 100, 125, and 150 μm NO₃⁻ as described in “Materials and Methods.” Data values are means ± se of five replicates. The fitted curve was obtained by direct fit to the Michaelis-Menten equation. Estimated K_m and V_max values are indicated in the figure. B, Low-affinity ¹³NO₃⁻ influx. Plants were grown for 4 weeks in 1 mm NH₄NO₃ and then nitrogen deprived for 1 week before being reexposed to 1 mm KNO₃ for 6 h. Nitrate influx was then measured at 1, 5, and 10 mm NO₃⁻. Data values are means ± se of four replicates.