Oxidoreductase activity of sorghum root exudates in a phenanthrene-contaminated environment

The effect of the polycyclic aromatic hydrocarbon (PAH) phenanthrene on the enzymatic activity of root exudates of the phytoremediating plant Sorghum bicolor (L.) Moench was studied. Analysis of sorghum root exudates allowed us to reveal the activities of oxidase, peroxidase, and tyrosinase. The activities of these enzymes were progressive as the soil phenanthrene concentration increased. Using lyophilized samples, we found that as a result of the enzymatic activity of the root exudates, some of the PAHs and products of PAH degradation were oxidized in the reaction mixture supplemented with the mediating agents (ABTS or DL-DOPA) but that no oxidation was observed in the reaction mixtures without the mediators. The revealed enzymatic activity of the sorghum root exudates may indicate the involvement of the root-released oxidoreductases in rhizospheric degradation of PAHs and/or their derivatives. In addition, from the data obtained, the coupling of plant and microbial metabolisms of PAHs in the rhizosphere may be surmised.