| The degradation of PCB typically occurs through initial reductive dechlorination under anaerobic conditions and subsequent phenol-ring cleavage under aerobic conditions. While some fungi and bacteria are able to express an enzyme known as nitrate reductase (NaR), plants primarily express this enzyme either constitutively in very low levels or upon induction by light and by nitrate, the substrate. In this study, we present our observations with plant NaR and its effect on PCB dechlorination, a relationship that had never been explored before. The incubation of 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153) during in vitro experiments of Zea mays and Medicago sativa NaR revealed a significant relationship between plant NaR and PCB dechlorination. Post-run GC-MS analysis revealed that NaR most likely transformed PCB 153 by initially removing the 4' carbon. The presence of a nitrate reductase gene---either nia1 or some unidentified highly similar isoform---in Medicago sativa was also verified via RT-PCR and confirmed via sequencing. Although real-time RT-PCR analysis was attempted, endpoint RTPCR analysis allowed the observation of NaR gene expression in nitrate-treated and untreated Medicago sativa plant tissue with greater NaR gene expression in the treated; this is parallel to NaR activity in such conditions. To our knowledge, the involvement of plant NaR in PCB dechlorination is a novel finding. This study is significant as it may be applied to bioremediation efforts of environmentally hazardous pollutants such as PCBs. |
