Hayashi, K.-i. et al. Proc. Natl. Acad. Sci. USA 111, 11557–11562 (2014).

Auxins are hormones with many developmental and physiological roles in plants. Their precise distribution is governed by a combination of synthesis, polarized transport, chemical inactivation and degradation. Reporters provide a spatial readout of signaling but cannot visualize the hormones themselves. Hayashi et al. report two fluorescent auxin analogs, NBD-NAA (7-nitro-2,1,3-benzoxadiazole conjugated to naphthalene-1-acetic acid) and NBD-IAA (NBD conjugated to indole acetic acid) to specifically tease out the effect of transport on auxin distribution in Arabidopsis thaliana. They show that the analogs do not participate in signaling for the most part, thus avoiding strong feedback regulation, but appear to be actively transported as expected for the auxins IAA and NAA. Results from these analogs also suggest the presence of an intracellular auxin gradient.