Plant secondary metabolites are involved in versatile functions on different levels in the plant organism. One of the roles is scavenging of free radicals and the protection against excess oxidation caused by UV irradiation, chemical oxidants or pathogen attack or other kinds of stress. Involved are phenolic compounds from different classes such as numerous phenol carboxylic acids, hydroxylated flavonoids such as flavones, flavonols, anthocyanins, procyanidins and isoflavonoids. Many of these substances have been isolated from plant species possessing valuable and intensively studied medicinal properties.
For assessment of the free radical scavenging and antioxidant capacity of phenolic complexes in plants the chemical in vitro (cell free) tests can be used for their relative simplicity and sometimes reasonable cost. Here, we will report the application of several antioxidant and anti-free radical spectrophotometric assays for testing the antioxidant abilities of some rarely studied plant species containing different classes of polyphenols. In addition, the antimutagenic bacterial assays were used to examine the in vivo genoprotective activity of these compounds against chemical mutagens. Among the investigated compounds there are lipophilic flavones from Scutellaria baicalensis and Iridaceae-type isoflavonoids from Belamcanda chinensis. Phenolic acids, procyanidins and flavonols containing Lamiaceae species such as Leonurus cardiaca, Lamium sp., Stachys betonica, Marrubium vulgaris, Galeopsis tetrahit have been also studied to comprise wider spectrum of different types of polyphenols. The antimutagenic activity of the extracted phenol complexes and isolated compounds correlates with free radical scavenging. In the Ames bacterial assays the direct mutagenesis by chemical mutagens can be distinguished from the mutagenesis induced by activation of pro-mutagen with cytochrome P-450 enzymatic microsomal fractions. Free radical scavenging by the low molecular weight compounds can play an important role as the last line of defense against oxidative damage of the cells for they are more stable than enzymatic antioxidant apparatus and can be easily accumulated in stress conditions (e.g. deposited in the cell wall or the vacuole). Superoxide scavenging can protect the cells against the production of deleterious peroxynitrite upon reaction of the relatively harmless superoxide with an important signaling molecule - nitric oxide. The in planta function of the antioxidant and antigenotoxic compounds should be further explored in order to obtain the complete insight into their role in protecting the plant cell.