Isolation and identification of polar auxin transport inhibitors from Saussurea costus and Atractylodes japonica

Abstract

An intensive survey of naturally-occurring regulators of polar auxin transport (PAT) was conducted in two oriental medicinal species from the Asteraceae, <em>Saussurea costus</em> and <em>Atractylodes japonica</em>, using the radish hypocotyl bioassay system and physicochemical analyses. Costunolide and santamarine were identified as well as dehydrocostus lactone from <em>S. costus</em> roots, and atractylenolide II and (+)-eudesma-4(14),7(11)-dien-8-one from <em>Atractylodes japonica</em> rhizomes as physiologically novel compounds possessing inhibitory activities of PAT. Costunolide and santamarine showed ca. 40% inhibition of PAT in the radish hypocotyl segments at a dose of 2.5 μg/plant and 1 μg/plant, respectively. Inhibitory effects of atractylenolide II and (+)-eudesma-4(14),7(11)-dien-8-one were ca. 10 times lower than those of costunolide and santamarine. Structure–activity relationships and possible mechanisms to inhibit PAT are also discussed.