Phytotoxic study of glycosylated flavonols from Annona coriacea (Annonaceae) on cultivated species and an invasive grass.

Abstract

Annona coriacea Mart. is a Brazilian native species whose phytotoxicity was described, although there is no data about the compounds responsible for it. The aim of this study was bioprospecting A. coriacea in relation to phytotoxicity on the elongation of wheat elongation coleoptiles and on germination and initial growth of standard target species (lettuce and tomato) and a weed (Urochloa decumbens (Stapf) R.D. Webster). Thus, the leaf ethanolic extract was subjected to chromatographic separation furnishing the isolation of 11 flavonols: 1 - Quercetin-3-O-gentiobioside, 2 - Quercetin-3-O-robinobioside, 3 - Rutin, 4 - Hyperin, 5 - Isoquercitrin, 6 - Biorobin, 7 - Nicotiflorin, 8 -Keioside, 9 - Narcissin, 10 - Cacticin and 11 - Isorhamnetin-3-O-glucoside. This is the first report of wheat coleoptile bioassay to all these compounds and it is also the first phytotoxicity results for 1, 2, 6, 8 and 10. Compounds 5, 7 and 11 showed elevated phytotoxicity in wheat coleoptiles bioassay (IC50 0.22 mM, r2 0.97; IC50 0.48 mM, r2 0.93; IC50 0.28 mM, r2 0.92, respectively). No correlation was found between the structure of the compounds and their activity. Compounds 5 and 11 were also tested on diaspores. Compound 11 significantly reduced the germination of U. decumbens in almost all concentrations, with values between 50% and 65%. The broad distinction concerning the complexity of the biological systems was suggested as an explanation for the distinct effects observed for coleoptile and germination and initial growth assays.