(A) Mutations in the ABP1 gene do not influence auxin-induced hypocotyl elongation. (B) Inhibition of the TIR1/AFB Aux/IAA auxin receptor by the dominant-negative axr3-1 protein completely blocks auxin-induced (10 µM NAA) hypocotyl elongation. The elongation triggered by fusicoccin (1 µM FC) is not affected in the same line. Both HS::axr3-1 and Col-0 seedlings were heatshocked 2 hr before auxin application. (C) Induction of the HS::axr3-1 line completely blocks the auxin-induced apoplastic pH drop. AreaKymo shows that in the control (Col-0 x apo-pHusion), apoplastic pH drops after addition of auxin (10 µM NAA), while this drop is absent in the HS::axr3-1 background. Each plot was constructed from 4 hypocotyl segments, both lines were heat-shocked 2 hr before imaging. (D) The auxin analogue, picloram (10 µM) triggers DR5::LUC auxin response; the response is slower than that of NAA (10 µM). Each curve corresponds to 4 hypocotyl segments, errorbars are stdev.s. (E) Picloram (10 µM) was applied before imaging, apoplastic pH drop occurs approximately 40 min later. An AreaKymo based on 3 hypocotyl segments; quantification is shown in the lower part of the panel. (F) A mutation in the AFB5 auxin co-receptor, afb5-5, leads to decreased sensitivity to picloram-induced hypocotyl elongation. On the left, a timecourse of elongation after 10 µM NAA or picloram is shown. On the right, a dose response curve of Col-0 and afb5-5 to NAA or picloram is presented. In A,B,F, curves correspond to 6 hypocotyl segments, errorbars represent stdev.s.