The Impacts of Plasticisers on Root Growth and Plant Systemic Signalling

Cook, Freya and Roberts, Mike and McAinsh, Martin and McAinsh, Martin and Roberts, Mike (2024) The Impacts of Plasticisers on Root Growth and Plant Systemic Signalling. Masters thesis, Lancaster University.

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Abstract

As plastic pollution continues and microplastics are generated from plastic breakdown in the environment, plasticiser leaching increases. This contaminates soils and aquatic systems, and bioaccumulates to amplify concentrations in organisms including crops grown for human consumption. Plasticisers, which are hydrocarbon chains added to plastics to increase flexibility, have been a subject of research for their impacts on mammalian health, as well as limited exploration into how they affect plant growth and physiology. To explore how plasticisers affect plant growth, and the mechanisms behind this, Arabidopsis thaliana was exposed to a selection of plasticisers with different uses and chemical structures. Seedlings were grown in agar containing a range of concentrations of plasticiser, and primary root length and secondary root number were recorded. The chemicals that impacted root architecture were used in further experiments, these were benzyl butyl phthalate (BBP), dimethyl phthalate (DMP), and dibutyl sebacate (DBS). Calcium signalling using bioluminescence, and auxin signalling using fluorescence were measured. 80 µg mL-1 of plasticiser had no impact on calcium signalling, but 800 µg mL-1 DMP induced higher calcium signalling over time and a signalling peak that was absent in other plasticiser and control experiments. In response to reactive oxygen species stress, plants grown in BBP and DMP had lower peak calcium signalling but elevated prolonged calcium signalling. Auxin signalling was elevated in the primary root of DMP-treated plants, and the secondary roots of those treated with BBP, DBS and DMP. These results implicate auxin accumulation and hydrogen peroxide stress in causing changes in root architecture observed from chronic plasticiser exposure, as well as demonstrate that DBS is harmful to plant growth, despite being previously characterised as a green alternative to plasticisers. This study provides a basis for further experiments into plasticiser interactions in soils and their effects on long-term plant development.