FIGURE 4.

Effect of NBPT on the development of the high-affinity urea uptake in maize roots. Five-day-old maize plants were exposed up to 24 h to a nutrient solution supplied with 0.5 mM urea in presence or absence of 0.897 μM NBPT (Urea + NBPT treatment or Urea treatment, respectively) or to a N-free nutrient solution, with or without NBPT (Control + NBPT treatment or Control treatment, respectively). Urea net uptake rate was measured by depletion from a solution containing 0.2 mM urea in a 10-min assay using plants collected at the indicated times during the treatment. Filled circles, Control treatment; open circles, Control + NBPT treatment; filled triangles, Urea treatment; open triangles, Urea + NBPT treatment; white and black bars, light and dark period, respectively. Data are means ± SD; letters refer to statistically significant differences within each time point among three independent biological replicates, underlined letters refer to overlapping data not significantly different among treatments; asterisks refer to statistically significant differences between each time point and time zero [Student–Newman–Keuls method ANOVA, n = 3, ^∗P < 0.05, ^∗∗P < 0.001].