Plant development displays an exceptional plasticity and adaptability that involves the dynamic, asymmetric distribution of the phytohormone auxin. Polar auxin flow, which requires transport facilitators of the PIN family, largely contributes to the establishment and maintenance of auxin gradients and mediates multiple developmental processes. Here, we report the effects of narciclasine (NCS), an Amaryllidaceae alkaloid isolated from Narcissus tazetta bulbs, on postembryonic development of Arabidopsis roots. Arabidopsis seedlings grown on NCS showed defects in root gravitropism which correlates with a reduction in auxin transport in roots. Expressions of auxin transport genes were affected and the polar localization of PIN2 protein was altered under NCS treatment. Taken together, we propose that NCS modulates auxin transport gene expression and PIN2 localization, and thus affects auxin transport and auxin distribution necessary for postembryonic development of Arabidopsis roots.