Exogenous application of GR24 in Arabidopsis was shown to alter the endocytic recycling of the auxin transporters PIN1 and PIN2 (Shinohara et al., 2013; Pandya‐Kumar et al., 2014). Therefore, we tested whether the increased biosynthesis of endogenous SL in PDR1 OE roots might have an effect on auxin distribution. The expression pattern and intensity of the auxin reporter pDR5:VENUS were investigated using confocal microscopy on 2‐wk‐old seedlings grown on 1/2 MS plates. Full image stacks of P. hybrida root tips showed that the signal intensity of pDR5:VENUS was weaker in PDR1 OE than in wild‐type plants (Fig. 8a, b). The inverted fountain pattern of auxin distribution reported for Arabidopsis (Swarup & Bennett, 2003) is also present in P. hybrida root tips and it is weakened in PDR1 OE roots (Fig. 8c), particularly in the central vasculature (Fig. 8d), where PIN1 is expressed. Cell expansion in the elongation zone (EZ) of PDR1 OE root tips is inhibited (Fig. 8e, f), probably explaining the proximity of the first root hair to the PDR1 OE meristematic zone. These results show that endogenous changes in SL transport and biosynthesis are capable of altering auxin distribution and support the hypothesis that SL is an upstream regulator of auxin transport in the root tip (Ruyter‐Spira et al., 2011).