Towards the characterization of radicals formed in rhizomes of Iris germanica

When Iris germanica, Hydrocotyle verticillata, Glyceria maxima and Juncus effusus plants were treated anoxically and subsequently returned to air, long-lived free radicals were rapidly generated in the plant tissues and were detected by EPR spectroscopy. The free radicals in I. germanica rhizomes were extracted into aqueous alkali; the EPR spectrum of the aqueous solution showed fine structure which indicated the presence of at least two oxygen-centred radicals. The EPR data, and the radical lifetimes, suggested that they were probably semiquinone radical anions. Product analysis of the alkaline extract indicated that the main components were a set of flavonoids including quercetin, irisolone, selenone and derivatives of irigenin. The main flavonoids had more reduced and/or more alkylated structures than those from I. germanica grown under normal aerobic conditions. Semiquinone radical anions can readily be generated from quercetin, and similar flavonoids with 1,2-dihydroxy-, 1,4-dihydroxy- or trihydroxy-substitution patterns, by interaction with superoxide. However, the EPR-detected radicals were probably derived from flavonoids more heavily substituted than quercetin.