Fig. 4.

TK VI-induced increase of auxin content and alteration of auxin response gradients in the Col-0 root tip. (A) TK VI-induced enhancement of IAA2 _pro :GUS expression in the Col-0 root tip. Six-day-old seedlings were transferred to medium without (MS) or with 5 μM TK VI for 12h before GUS staining. (B) Time course of expression of IAA2 in response to TK VI treatment. (C) Free IAA measurement in Col-0 root tips in response to TK VI treatment. Six-day-old Col-0 seedlings were transplanted to medium without (Control) or with 5 μM TK VI for 3h before the 2mm root tips were harvested. Free IAA levels were then measured. The error bars represent the SD of triplicate measurements. The asterisks denote Student’s t-test significance compared with untreated plants: *P<0.05.

(D) Time course of expression of auxin biosynthesis-related genes in response to TK VI treatment. For (B) and (D), 6-day-old Col-0 seedlings were treated with 5 μM TK VI for the indicated time periods, and the 2mm root tips were harvested for RNA extraction and qRT–PCR analysis. Transcript levels of the indicated genes in Col-0 without TK VI treatment were arbitrarily set to 1. The error bars represent the SD of triplicate reactions.

(E, F, G, H) TK VI-induced disturbance of DR5 _pro :GUS expression in the Col-0 root tip. Six-day-old seedlings were transferred to medium without (MS) or with 5 μM TK VI for the indicated times before GUS staining. (I) TK VI-induced repression of acropetal and basipetal auxin transport. Six-day-old Col-0 seedlings were transplanted to medium without (Control) or with 5 μM TK VI for 24h before acropetal and basipetal auxin transport assays were performed. The acropetal and basipetal auxin transport levels without TK VI treatment were arbitrarily set to 100%. Data shown are mean values of five biological repeats with the SD. The asterisks denote Student’s t-test significance compared with untreated plants: **P<0.01. Scale bars=50 µm (A, E, F, G, H).