South China Institute of Botany, Chinese Academy of Sciences, Guangzhou, Guangdong, 5106550, China.
Journal of Chemical Ecology 31: 1657–1668, (2005).
Phytotoxicity-directed extraction and fractionation of the aerial parts of Mikania micrantha H.BX. led to the isolation and identification of three sesquiterpenoids: dihydromikanolide, deoxymikanolide and 2,3-epoxy-l-hydroxy-4,9-germacradiene-12,8: 15,6-diolide. These sesquiterpenoids inhibited both germination and seedlins growth with of tested species with deoxymikanolide possessing the strongest phytotoxicity. In a bioassay against lettuce (Lactuca sativa.L.), deoxymikanolide reduced radicle elongation at low concentration (IC50=47 μglml); dihydromikanolide showed a weaker effect (IC50=9(j(°μ glml), and 2,3-epoxy-I-hydroxy-4,9-germacradiene 12,8: 15,6-diolide exhibited the least effect (IC50=242 μglml). Deoxymikan olide caused yellowish lesions at the root tips of lettuce at a concentration of 50 μglml, and a 250 μglml solution killed lettuce seedlings. A bioassay against the monocot ryegrass (Lolium multiforum) revealed similar results on radicle elongation, which implied that the growth inhibition by these compounds was not selective. To evaluate their phytotoxicity to plants in natural habitats, three common companion/tree species in south China, Acacia mangium, Eucalyptus robusta and Pinus massoniana, were also tested and similar results were obtained. This is the first report on the isolation of 2,3 epoxy-I-hydroxy-4,9-germacradiene-12,8: 15,6-diolide as a naturally occurring product.
