Role of Eucalyptus globulus wound wood extractives:: evidence of superoxide dismutase-like activity

Superoxide dismutase-like activity of crude Eucalyptus globulus extracts obtained from new wound wood was measured using the water-soluble tetrazolium salt (WST)-1 assay. This in vitro assay determined the activity of superoxide radicals scavenging in a xanthinc oxidase system. The 50% inhibition (IC50) of formazan formation was estimated for fractionated samples and purified compounds isolated from the crude wound wood extract, i.e. engelitin and pedunculagin. Standards of gallic acid and pentagalloyl glucose were also measured. Fraction II as well as the compounds pentagalloyl glucose and pedunculagin showed the highest levels of antioxidant activity. Subsequent analysis of fraction II by high-performance liquid chromatography (HPLC) coupled with negative ion electrospray. mass spectrometry revealed the fraction to be dominated by hydrolysable tannins including pedunculagin, di-, tri- and tetragalloylglucoses. These preliminary results provide some evidence for an antioxidant role of secondary metabolites in tree wound repair and defence.