A common auxin that does not respond to gravity’s pull in land plants

June 25, 2015

This surprising revelation regarding the characteristics of plant hormones could provide hints on the mechanism of potent herbicides

An international research group including RIKEN CSRS researchers investigated the characteristics of two naturally occurring auxins, indole-3-acetic acid (IAA) and phenylacetic acid (PAA), and determined that IAA is actively transported in maize coleoptiles in the gravitropic direction, but PAA is not. When IAA was administered to an Arabidopsis mutant with lowered auxin levels and no gravitopic response in the roots, the mutant’s root gravitropism was restored. However, the addition of PAA did not restore gravitropism, similarly to the case of the synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D), a potent herbicide. These results demonstrate that PAA and 2,4-D are not actively transported in a polar manner and are not affected by gravity.

The findings raise the possibility that plants coordinately regulate growth and morphogenesis using two auxins with different transport characteristics. Further clarification of the transport mechanisms and physiological roles of PAA could benefit the development of high-safety pesticides and new plant growth regulating agents.


Original article
Plant & Cell Physiology doi: 10.1093/pcp/pcv088
S. Sugawara, K. Mashiguchi, K. Tanaka, S. Hishiyama, T. Sakai, K. Hanada, K. Kinoshita-Tsujimura, H. Yu, X. Dai, Y. Takebayashi, N. Takeda-Kamiya, T. Kakimoto, H. Kawaide, M. Natsume, M. Estelle, Y. Zhao, K. Hayashi, Y. Kamiya, H. Kasahara,
"Distinct characteristics of indole-3-acetic acid and phenylacetic acid, two common auxins in plants".

Hiroyuki Kasahara
Senior Research Scientist
Plant Productivity Systems Research Group