Distribution of (-)-Hamanasic Acid A in South American Species of Flourensia and Phytotoxic Effects of Leaf Aqueous Extracts

Abstract

The presence of the phytotoxic sesquiterpene (-)-hamanasic acid A {(-)HAA; 7-carboxy-8-hydroxy-1(2), 12(13)-dien-bisabolene} isolated from Flourensia campestris ( FC), was investigated in the South American species of the genus, together with the evaluation of the phytotoxic activity of their leaf aqueous extracts. (-)HAA was identified and isolated from F. fiebrigii ( FF) and F. oolepis ( FO), being chemically (GC-MS, NMR, [α]D) and biologically (bioassayed on lettuce) indistinguishable from that of FC, while no (-)HAA was found in F. hirta ( FH), F. riparia ( FR) and F. niederleinii ( FN). Its leaf content in FF was similar to that found in FC (ca. 15 mg g−1 WT) and significantly higher than in FO (0.8 mg g−1 WT). The screening for the presence of (-)HAA in other species of Flourensia communities showed that its natural occurrence is restricted only to Flourensia species. No (-)HAA could be detected in any of the 37 -most representative- species of these communities (26 natives, 11 exotics), despite many of them belong to the same family and tribe as Flourensia spp. Leaf aqueous extracts of all Flourensia species exhibited strong inhibitory effects on lettuce germination and on root and shoot growth, regardless of the presence and content of (-)HAA. These results strongly suggest the existence of other powerful phytotoxic compounds in those Flourensia spp lacking (-)HAA. Our results clearly show that (-)HAA only pertains to some species of the genus Flourensia. Relative to previous exomorphologic groupings of the genus, our chemotaxonomic data would give support to the close link described between FC and FF, but not with FR. In addition, the fact that (-)HAA was also found in FO, which belongs to a second different line, also points out that species position in this lineage would deserve to be revisited. The restricted production of (-)HAA by Flourensia in their communities suggests its special link with the genus, and sustains its putative allelochemical role.