Activation of auxin transcriptional reporter by IAA and IPA-N3. (a,b) The induction of DR5rev::GFP reporter in the root tip (a), and trichoblasts (b), could be observed 4 h after the IAA and IPA-N3 application (5 μM). Note the accumulation of the ER-targeted GFP expressed from the auxin inducible DR5rev promoter in epidermal cells (arrowheads). Propidium iodide was used as counterstain to outline cells (red channel). (c) Sensitive auxin-induced degradation domain-based R2D2 reporter scanned at t1 = 10 min after IPA-N3 application (5 μM) and t2 = 15 min after application. Note the disappearance of the DII: n3Venus signal (arrowheads). (d) Quantification of the ratio between the red signal (mDII: ntdTomato; auxin insensitive) and green signal (DII: n3Venus; auxin sensitive) at time points t1 and t2. Mean of measurement from 5 cells ± SE. *p < 0.05 (Student’s t-test). (e) Quantitative RT-PCR on four auxin-regulated genes. Three tested genes were significantly induced after 1 h incubation with 1 μM of IPA or IPA-N3 potency with less than 1 μM IAA. The mean values of at least 7 measurements ± SE. *p < 0.01 (Student’s t-test). Scale bars = 20 μm (a), 10 μm (b,c).