Figure 3.

Local Ammonium Supply Induces Third-Order Lateral Root Branching.

(A) and (B) Typical root morphology of wild-type plants grown on vertically split agar plates with the first lateral root growing into an HN compartment with 0.8 mM KNO₃ (A) or 0.8 mM NH₄Cl (B) and the remainder of the roots growing in 5 μM KNO₃ (LN).

(C) to (F) Quantitative assessment of root morphology (C), second-order lateral root (LR) length, second-order lateral root density (D), third-order lateral root length (E), and third-order lateral root density (F).

(G) to (I) ¹⁵N uptake from ¹⁵N-labeled nitrate or ammonium applied to the HN side and its distribution in plants. Concentrations of total nitrogen (¹⁴N+¹⁵N, outer bars) and ¹⁵N (inner bars) in roots grown on the HN side (G), or roots grown on the LN side (H), and (I) shoots are indicated. Plants were grown on vertically split agar plates for 15 d on either local nitrogen supply (5 μM NO₃⁻ on the LN side with 0.8 mM NO₃⁻ or NH₄⁺ on HN side; LN versus NO₃⁻LN versus NH₄⁺) or homogenous nitrogen supply (0.8 mM NO₃⁻ or NH₄⁺ on both sides; NO₃⁻ versus NO₃⁻NH₄⁺ versus NH₄⁺). Bars represent mean values (±se) of 10 to 20 individual plants, and different letters for total nitrogen (¹⁴N+¹⁵N, outer bars) and ¹⁵N (inner bars) denote significant differences among means at P < 0.05 (Tukey’s test). DW, dry weight.