Growth regulators are important in ornamental plants and horticultural crops that otherwise would require labor-intensive manipulation and pruning. The inhibitors keep plants a desired size and shape, and control fruit formation by blocking the transport of auxin, a hormone that controls growth processes. Current growth inhibitors are often toxic to humans.

Ken-ichiro Hayashi and co-workers, Okayama University of Science, Japan, have developed a new class of plant growth regulators that are expected to be less toxic to humans. The inhibitors are 5-alkoxy derivatives of indole 3-acetic acid and 7-alkoxy derivatives of naphthalene 1-acetic acid. In particular, the hexyloxy and benzyloxy derivatives were shown to act as potent inhibitors of auxin transport. The bulky groups prevented movement of the inhibitors out of the cells, creating inactive auxin analogs for auxin signaling.

• Alkoxy-auxins Are Selective Inhibitors of Auxin Transport Mediated by PIN, ABCB, and AUX1 Transporters
  E. Tsuda, H. Yang, T. Nishimura, Y. Uehara, T. Sakai et al.,
  J. Biol. Chem. 2011, 286, 2354–2364.
  DOI: 10.1074/jbc.M110.171165