To assess whether PDR1‐dependent SL transport may be involved in root hair elongation, we performed time‐lapse analyses using light‐sheet confocal microscopy (Maizel et al., 2011; Stelzer 2015; von Wangenheim et al., 2016) on emerging lateral roots of seedlings transgenic for pPDR1:nls‐YFP and pPIN‐FORMED 1 (PIN1):nls‐RFP, the latter involved in SL‐regulated auxin transport (Shinohara et al., 2013) and used here as a morphological reference for the vasculature. As P. hybrida roots, owing to their thickness, proved to be unsuitable for this analysis, we chose A. thaliana plants transgenic for the same reporters. The time‐lapse analysis (Movie S5) revealed that pPDR1 is activated in epidermal cells as soon as root hairs elongate, and stops its activity when root hairs are fully elongated (Fig. S3h–k), implying that SL transport plays a key role during root hair elongation but not after root hairs have reached their final size. The sequential appearance of pPDR1:nls‐YFP and pPIN1:nls‐RFP (Fig. S7l,m) suggests a temporal order of hormonal action during root hair elongation.