The major indole alkaloid N,β-D-glucopyranosyl vincosamide from leaves of Psychotria leiocarpa Cham. & Schltdl. is not an antifeedant but shows broad antioxidant activity

Abstract

N,β-D-glucopyranosyl vincosamide (GPV), a major alkaloid of Psychotria leiocarpa, constitutes up to 2.5% of the dry weight in leaves. Alkaloid content was not elicited by mechanical wounding or jasmonate. At concentrations found in natural conditions or 2.5 fold higher, GPV did not inhibit herbivory in two unrelated generalist models (Helix aspersa and Spodoptera frugiperda) or in a specific interaction model (Heliconius erato fed with Passiflora suberosa). In situ staining assay showed quenching activity of hydrogen peroxide by GPV. Exposure of P. leiocarpa to acute UV-B stress did not change GPV or chlorophyll content, indicating high tolerance to this stress by the species. In vitro antioxidant tests against singlet oxygen, superoxide anions and hydroxyl radicals showed efficient quenching activity of the alkaloid. GPV was not effective as antifeedant, but it may act indirectly in P. leiocarpa protection against oxidative stress generated upon wounding, UV exposure and perhaps other environmental stresses.

Keywords:

• monoterpene indole alkaloid (MIA)
• herbivory
• wounding
• jasmonate
• phytoanticipin
• UV-B radiation
• reactive oxygen species

Acknowledgements

Research was supported by grants from National Council for Scientific and Technological Development (CNPq-Brazil). The authors are grateful to Dr Lúcia Bertholdo Vargas (Center for Biotechnology, University of Caxias do Sul, Brazil) for Spodoptera frugiperda larvae, Dr Gilson Rudinei Pires Moreira (Department of Zoology, UFRGS) for Heliconius erato larvae and Dr Amélia Teresinha Henriques (Faculty of Pharmacy, UFRGS) for lending the MPLC equipment used in part of the GPV purification protocol.