Figure 6

Characterization of High and Low NO3− Transport Systems (HATS and LATS, respectively). Plants were grown hydroponically on 2 mM NO3− for 7 days, then N starved for 8 days (−N, open circles and dashed lines) or N starved for 6 days and induced with 1 mM NO3− for 24 h (+NO3−, closed circles and solid lines). (a) 15NO3− influx at external concentrations ranging from 0.01 to 10 mM 15NO3−. (b) 15NO3− influx at external concentrations ranging from 0.01 to 0.2 mM 15NO3−. HATS kinetics were fitted with Michaelis-Menten curves (Influx = Vmax * [15NO3−]/(Km + [15NO3−]). Vmax and Km values were obtained by linear regression on the Lineweaver-Burk representation (1/Influx = a * (1/[15NO3−]) + b, with Vmax = 1/b and Km = a/b). cHATS and iHATS: constitutive and inducible HATS (respectively). (c) iHATS influx at external concentrations of 0.01–0.2 mM 15NO3−, obtained by subtracting −N values from +NO3− values in panel b and fitted with Michaelis-Menten curve. (d) LATS 15NO3− influx at external concentrations ranging from 0.5 to 10 mM 15NO3−, obtained by subtracting HATS Vmax values (panel b) from corresponding influx values (panel a). LATS kinetics were fitted with linear curves. cLATS and iLATS: constitutive and inducible LATS (respectively). (e) iLATS curve, obtained by subtracting values from −N condition to values from +NO3− condition in panel d, fitted with a linear curve. Values correspond to the mean of 5 biological replicates +/−SD.