<i>cis</i>-Cinnamic Acid Selective Suppressors Distinct from Auxin Inhibitors

Abstract

The activity of cis-cinnamic acid (cis-CA), one of the allelochemicals, in plants is very similar to that of indole-3-acetic acid (IAA), a natural auxin, and thus cis-CA has long been believed to be an analog of auxin. We have reported some structure-activity relationships studies by synthesizing over 250 cis-CA derivatives and estimating their inhibitory activities on root growth inhibition in lettuce. In this study, the compounds that showed low-or no-activity on root growth inhibition were recruited as candidates suppressors against cis-CA and/or auxin and tested for their activity. In the presence of cis-CA, lettuce root growth was inhibited; however, the addition of some cis-CA derivatives restored control-level root growth. Four compounds, (Z)-3-(4-isopropylphenyl)acrylic acid, (Z)-3-(3-butoxyphenyl)acrylic acid, (Z)-3-[3-(pentyloxy)phenyl]acrylic acid, and (Z)-3-(naphthalen-1-yl)acrylic acid were selected as candidates for a cis-CA selective suppressor they allowed the recovery of root growth from inhibition by cis-CA treatment without any effects on the IAA-induced effect or elongating activity by themselves. Three candidates significantly ameliorated the root shortening by the potent inhibitor derived from cis-CA. In brief, we have found some cis-CA selective suppressors which have never been reported from inactive cis-CA derivatives for root growth inhibition. cis-CA selective suppressors will play an important role in elucidating the mechanism of plant growth regulation.

Essential structural features of (2Z,4E)-5-phenylpenta-2,4-dienoic acid for inhibition of root gravitropism

“…Therefore, we endeavored to discover inhibitors of gravitropic bending that did not suppress primary root elongation among our synthetic analogues of cis-CA. After screening the synthetic cis-CA analogues, especially the less potent elongation inhibitory compounds (Okuda et al, 2014), we found that (2Z,4E)-5-phenylpenta-2,4-dienoic acid (ku-76, Figure 2) inhibited root gravitropism at 5 M, but did not repress primary root elongation at the 5-50 M (Fujii et al, 2016). As such, ku-76 was considered to specifically target regulatory component of root gravitropic bending.…”

Design and synthesis of strong root gravitropism inhibitors with no concomitant growth inhibition

“…cis-CA has also been reported to have inhibitory activity of auxin efflux 18 . We previously reported that cis-CA is localized at the root tip of lettuce by molecular imaging experiments using fluorescent molecular probes of cis-CA [21][22][23][24] . Based on these results, we subsequently focused on the effect of cis-CA on the gravitropism of plants and observed that it inhibits not only lettuce root elongation but also gravitropic bending of the roots, that is, cis-CA is a non-selective inhibitor of both elongation and gravitropic bending.…”