title: A 2,4-dichlorophenoxyacetic acid analog screened using a maize coleoptile system potentially inhibits indole-3-acetic acid influx in Arabidopsis thaliana.
abstract: Studies using inhibitors of indole-3-acetic acid (IAA) transport, not only for efflux but influx carriers, provide many aspects of auxin physiology in plants. 1-Naphtoxyacetic acid (1-NOA), an analog of the synthetic auxin 1-N-naphtalene acetic acid (NAA), inhibits the IAA influx carrier AUX1. However, 1-NOA also shows auxin activity because of its structural similarity to NAA. In this study, we have identified another candidate inhibitor of the IAA influx carrier. The compound, "7-B3; ethyl 2-[(2-chloro-4-nitrophenyl)thio]acetate," is a 2,4-dichlorophenoxyacetic acid (2,4-D) analog. At high concentrations (> 300 µM), 7-B3 slightly reduced IAA transport and tropic curvature of maize coleoptiles, whereas lower concentrations had almost no effect. We have analyzed the effects of 7-B3 on Arabidopsis thaliana seedlings. 7-B3 rescued the 2,4-D-inhibited root elongation, but not the NAA-inhibited root elongation. The effect of 7-B3 was weaker than that of 1-NOA. Both 1-NOA and 7-B3 inhibited DR5::GUS expression induced by IAA and 2,4-D, but not that induced by NAA. At high concentrations, 1-NOA exhibited auxin activity, but 7-B3 did not. Furthermore, 7-B3 inhibited apical hook formation in etiolated seedlings more effectively than did 1-NOA. These results indicate that 7-B3 is a potential inhibitor of IAA influx that has almost no effect on IAA efflux or auxin signaling.
authors.affiliation: Department of Biological Sciences; Tokyo Metropolitan University; Tokyo, Japan.
authors.forename: Hiromi
authors.initials: H
authors.lastname: Suzuki
authors.affiliation: Department of Biological Sciences; Tokyo Metropolitan University; Tokyo, Japan.
authors.forename: Naoyuki
authors.initials: N
authors.lastname: Matano
authors.affiliation: Department of Biological Sciences; Tokyo Metropolitan University; Tokyo, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Nishimura
authors.affiliation: Department of Biological Sciences; Tokyo Metropolitan University; Tokyo, Japan.
authors.forename: Tomokazu
authors.initials: T
authors.lastname: Koshiba
keywords: 1-NOA; 2,4-D; AUX/LAX; Apical hook; Arabidopsis; IAA influx inhibitor