Studies of the Uptake of Nitrate in Barley : II. Energetics.

Q(10) values for (13)NO(3) (-) influx were determined in ;uninduced' (NO(3) (-)-starved) and ;induced' (NO(3) (-)-pretreated) roots of barley (Hordeum vulgare L.) plants at various concentrations of external NO(3) (-) ([NO(3) (-)](0)). At 0.02 mole per cubic meter [NO(3) (-)](0), Q(10) values for influx were from 3 to 4 between 5 and 10 degrees C. As [NO(3) (-)](0) increased Q(10) values decreased, reaching values of 1.2 and 2.0, respectively, at 20 moles per cubic meter in uninduced and induced plants. The metabolic dependence of (13)NO(3) (-) influx at low and high [NO(3) (-)](0) (0.1 and 20.0 moles per cubic meter, respectively) in uninduced and induced plants was probed by the use of various inhibitors. These experiments confirmed the findings of the Q(10) studies, demonstrating that at low [NO(3) (-)](0) (13)NO(3) (-) influx was extremely sensitive to metabolic inhibition. By contrast, at high [NO(3) (-)](0), influx was relatively insensitive to the presence of inhibitors.