Figure 7.

Unidirectional influx of ${\text{NO}}_3^{-}$ and ${\text{NH}}_4^{+}$into the roots of maize genotypes grown at either 0.5 mM or 2.5 mM ${\text{NO}}_3^{-}$. Panels (A,B) show the relationships between the fluxes of either ${\text{NO}}_3^{-}$ (A) or ${\text{NH}}_4^{+}$ (B) for each ${\text{NO}}_3^{-}$ treatment; the relationship between the fluxes for each ${\text{NO}}_3^{-}$ treatment is shown in Panels (C,D). Nitrate and ${\text{NH}}_4^{+}$ influx were measured using¹⁵N labeled ${\text{NO}}_3^{-}$ or ${\text{NH}}_4^{+}$ over a 10-min influx period from a 200 μM solution.