Unraveling the impact of nano-microscale polyethylene and polypropylene plastics on Nicotiana tabacum: Physiological responses and molecular mechanisms

Abstract

Plastics, as emerging pollutants, are increasingly found in soil, yet their systemic impact on soil ecosystems and plants remains poorly understood. This study explores the impacts of Polypropylene (PP) and Polyethylene (PE) microplastics, of varying sizes (20 nm and 100 µm) and doses (100 and 1000 mg/kg), on tobacco plant growth. Over a 55-d exposure period, PP and PE MPs exhibited a dose-dependent effect on the growth of tobacco plants. Notably, both PE and PP exposures significantly suppressed plant height, as well as fresh and dry biomass, with PP demonstrating greater toxicity. However, an exception was observed in the PP treatment, with marginal yet notable increase in growth indicators was recorded at a 20 nm particle size under high-concentration exposure. Further investigations revealed that MPs exposure at varying concentrations negatively impacted photosynthetic activity and triggered oxidative stress in leaves, with higher-dose treatments leading to a more pronounced accumulation of reactive oxygen species (ROS). To elucidate the molecular response mechanisms of tobacco leaves under PP-MP stress, a co-omics analysis was conducted. The analysis identified key pathways involved in the plant’s response to PP-MP stress, including plant hormone signal transduction, the MAPK signaling, flavonoid and phenylpropanoid biosynthesis, and photosynthesis antenna proteins. A comprehensive assessment of genes and metabolites revealed significant alterations in the biosynthesis of several plant hormones and flavonoids, including auxin, cytokinin, abscisic acid (ABA), and jasmonic acid. These findings suggest that plastics may impair photosynthetic efficiency, alter hormonal responses, and cause redox imbalance, ultimately affecting plant growth and resilience.