MOLECULAR METHODS FOR ASSESSING THE RESPONSE OF ARABIDOPSIS THALIANA PLANTS TO POLYCHLORINATED BIPHENYLS AND HYDROXYLATED POLYCHLORINATED BIPHENYLS

Abstract

Polychlorinated biphenyls (PCBs) are a class of persistent organic contaminants that are ubiquitous and persistent in the environment. In the environment, PCBs have been shown to undergo various degradation processes and generate hydroxylated metabolites known as hydroxylated polychlorinated biphenyls (OH-PCBs). There is a growing scientific interest in studying OH-PCBs as they are being increasingly detected in biotic and abiotic samples. Due to their widespread presence in the air, water, and soil, as well as their ability to bioaccumulate in living organisms, they pose a high danger to human beings and thus need to be remediated. Though phytoremediation has been proposed as a useful technology for the environmental management of PCBs, there is a lack of information about potential phytoremediation of OH-PCBs The hypothesis underlying this study is that hydroxylation of PCBs to OH-PCBs results in different toxicity and physiological effects on plants. In order to test this hypothesis, we conducted experiments aimed at understanding the toxicity and metabolism of PCBs and OH-PCBs by A. thaliana plants at physiological and transcriptomic levels. The applicability of FTIR to analyze lignin and cellulose content in the cell wall was tested for the purpose of biofuel production. More precisely, the specific aims of this study are as follows: 1. To determine the toxicity of selected PCBs and their hydroxylated metabolites (OH-PCBs) toward the model plant A. thaliana. 2. To understand the regulation of the response to and metabolism of PCBs and OH-PCBs in exposed A. thaliana at the transcriptomic level. 3. To determine the change in the biomass composition of A. thaliana upon exposure to different PCBs and OH-PCBs. Toxicity results indicated no observable toxicity of the parent PCBs toward the plants. However, lower chlorinated OH-PCBs resulted in a significant reduction in the growth and germination rate of the plants. Genome wide expression microarrays were used to investigate the transcriptional response of A. thaliana plants to 2,5-DCB and three of its OH-metabolites. Exposure to 2,5-DCB caused up-regulation of genes that are involved in toxic stress response and detoxification functions, and induction of multiple xenobiotic response genes. FTIR analysis was used to determine the effects of different PCBs and their hydroxylated metabolites on the composition of the plant biomass. Significant changes in the lignin and cellulose content were observed between different treatments, which indicated an overall effect on the cell wall components upon exposure to PCBs and its OH metabolites.