Figure 8.

Role of Auxin in Fe-Dependent Lateral Root Elongation.

(A) and (B) Expression of the auxin-responsive reporter DR5-GUS in emerged (A) and elongating (B) lateral roots. Fe-EDTA (10, 50, or 200 μM) was supplied either homogenously to all three agar segments or locally to the middle agar segment. Lateral roots were analyzed by light microscopy after 7 d of treatments (n > 10 seedlings). The experiments were repeated twice and representative lateral roots are shown. Bars = 100 μm.

(C) Experimental setup for supplying NPA either to leaves or to the primary root tip.

(D) Elongation rate of lateral roots of wild-type (Col-0) plants supplied locally with 50 μM Fe and treated with the auxin transport inhibitor NPA on leaves or on the primary root tip. Seeds were germinated on Fe-free, half-strength MS medium for 7 d. Seedlings were then transferred to segmented agar plates supplied with 50 μM Fe in the middle segment and on which the shoot or the primary root tip was placed over a fourth segment. After 7 d, 5 μM NPA was supplied either to the leaves or to the primary root tip. Lateral root length was measured every day from days 6 to 9 to determine lateral root growth rate before and after NPA treatments. Bars indicate means ± se; n = 6 plates with three plants each. Different letters indicate significant differences among means (P < 0.05 by Tukey’s test).