Enzymes in plant metabolism of PCBs and PAHs

Abstract

Recently it has been shown that plants are able to transform polychlorinated biphenyls (PCBs) as well as polycyclic aromatic hydrocarbons (PAHs), but the knowledge of enzymes involved in these metabolic processes is limited. Plant peroxidases generally play an important role in plant metabolism. On the other hand, cytochrome P450 is involved in the detoxification of various xenobiotics in the cells of higher organisms. In this work, several in vitro cultures of different plant species were screened for their ability to transform PCBs or PAHs, and compared regarding their total extra- and intracellular peroxidase activity. Cultures with good transformation ability exhibited in the presence of xenobiotics the same or higher levels of peroxidases as the controls incubated without contaminants. Cultures with markedly lower peroxidase activity exhibited also lower PCB/PAH conversion in the presence of PCBs/PAHs. It was attempted to identify lignin peroxidase and Mn-peroxidase in plants, originally described in white rot fungi to be responsible for the degradation of PCBs and other environmental pollutants. In addition to different types of peroxidases, RBBR oxidase was also detected in plants. The decolourisation of RBBR during the growth on agar plates was used as a rough screening method for plant cells able to metabolise PCBs/PAHs efficiently. The exact type of transformation reaction (peroxidative or oxidative) was studied using various inhibitors and inducers of peroxidases and cytochrome P450. It was shown that both enzymatic systems are partially involved in the detoxification mechanism of chosen xenobiotics in plants.