Effects of Polychlorinated Biphenyls (PCBs) and Their Hydroxylated Metabolites (OH-PCBs) on Arabidopsis thaliana

Abstract

Plants metabolize polychlorinated biphenyls (PCBs) into hydroxylated derivatives (OH-PCBs), which are sometimes more toxic than the parent PCBs. The objective of this research was to compare the toxicity of a suite of PCBs and OH-PCBs toward the model plant, Arabidopsis thaliana. While parent PCBs and higher-chlorinated OH-PCBs exhibited a low or nondetectable toxicity, lower-chlorinated OH-PCBs significantly inhibited the germination rate and plant growth, with inhibition concentration 50% (IC50) ranging from 1.6 to 12.0 mg L−1. The transcriptomic response of A. thaliana to 2,5-dichlorobiphenyl (2,5-DCB), and its OH metabolite, 4′-OH-2,5-DCB, was then examined using whole-genome expression microarrays (Affymetrix). Exposure to 2,5-DCB and 4′-OH-2,5-DCB resulted in different expression patterns, with the former leading to enrichment of genes involved in response to toxic stress and detoxification functions. Exposure to 2,5-DCB induced multiple xenobiotic response genes, such as cytochrome P-450 and glutathione S-transferases, potentially involved in the PCB metabolism. On the contrary, exposure to both compounds resulted in the down-regulation of genes involved in stresses not directly related to toxicity. Unlike its OH derivative, 2,5-DCB was shown to induce a transcriptomic profile similar to plant safeners, which are nontoxic chemicals stimulating detoxification pathways in plants. The differentiated induction of detoxification enzymes by 2,5-DCB may explain its lower phytotoxicity compared to 4′-OH-2,5-DCB.

Transcriptomic response of Arabidopsis thaliana exposed to hydroxylated polychlorinated biphenyls (OH-PCBs)

“…Understanding the effects of PCBs and OH-PCBs on plants is significant because plants are the basis of the terrestrial food web and can be used for soil remediation (i.e., phytoremediation). In a prior publication, we reported that a suite of lowerchlorinated OH-PCBs were highly toxic for the model plant, Arabidopsis thaliana, while most parent PCBs did not show significant effects (Subramanian et al, 2017). Gene expression analysis using 2,5-dichlorobiphenyl (2,5-DCB) and its OH-derivative, 4'-OH-2,5-DCB, showed that the parent compound -unlike the OH-derivative -induced multiple xenobiotic response genes, such as cytochrome P-450 and glutathione Stransferases, potentially involved in the PCB metabolism, which may explain the lower phytotoxicity of PCBs as compared with their OH-derivatives.…”

“…A. thaliana, ecotype Columbia (Col-0/Redei-L211497, Ohio State University, Columbus, OH) was grown as we described in Subramanian et al (2017). In short, surface-sterilized seeds were germinated in Petri dishes containing semi-solid, half-strength Murashige & Skoog (MS) medium (0.3% sucrose) supplemented with increasing concentrations of 2,5-DCB, 2'-OH-, 3'-OH-, and 4'-OH-2,5-DCBs.…”

“…After 21 days of growth, plantlets were removed from the medium, treated with RNAlater™ (Ambion, Foster City, CA) and stored at −80°C until RNA extraction. RNA was extracted from the whole plants using TRIzol ® Plus RNA Purification kit with on-column PureLink ® DNase treatment (Thermofisher, Waltham, MA) as described in Subramanian et al (2017). RNA was analyzed by the absorbance ratios OD(optical density) 260/OD280 and OD260/OD230 (NanoDrop™ ND-2000, Vernon Hills, IL).…”

“…Quantitative analysis of gene expression was performed for a subset of genes using reversetranscription real-time PCR (RT-qPCR) as described in Subramanian et al (2017). Six genes -three upregulated and three downregulated across all treatments -were selected for the analysis.…”

PCBs risk evaluation, environmental protection, and management: 50-year research and counting for elimination by 2028

“…However, most plant species cannot absorb and accumulate lipophilic PCBs through their root systems. Some congeners and their metabolites are toxic to plants species (Subramanian et al 2017). Researchers report successful use of plants as passive biomonitors of PCBs in ambient air as shown by 25 years of PCB biomonitoring by the Bavarian EPA (Weber et al 2017).…”