A major shoot-specific
monoterpene indole alkaloid produced by Psychotria brachyceras,
brachycerine, is regulated by either wounding or
jasmonate application. Highest concentrations of the
alkaloid are found in inflorescences, suggesting a defence role.
Brachycerine has antimutagenic and
antioxidant properties, capable of quenching
singlet oxygen,
hydroxyl radical, and
superoxide. This study aimed at characterizing the putative role of
brachycerine in P. brachyceras responses to wounding and herbivory. Damage to leaves increased the content of
brachycerine locally. Wounding did not affect phenolics content in P brachyceras leaves, and no
tannins were detected in the species. In generalist herbivore bioassays, neither
brachycerine nor P. brachyceras extracts showed toxic effects. In vivo
hydrogen peroxide staining assay showed less
wound-generated
peroxide accumulation in
alkaloid treated tissues. This pattern was confirmed in quantitative assays measuring tissue
hydrogen peroxide concentrations. Data indicate that
brachycerine is not a herbivore deterrent, but rather an indirect chemical defence, modulating oxidative stress caused by mechanical damage.