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Influence of polyethylene microplastics on Brassica rapa: Toxicity mechanism investigation
Summary
Researchers exposed the fast-growing plant Brassica rapa (related to turnip and cabbage) to polyethylene microplastics that had been degraded by sunlight, finding that the plastics stunted plant growth by up to 51% and triggered cellular stress responses. Genetic analysis revealed the microplastics disrupted the plant's immune and growth pathways, providing insight into how plastic pollution in agricultural soil could affect food crops.
Polyethylene microplastics (PE-MPs) have toxicity to ecological environment, including animals and plants. This study investigated the toxicity of photodegraded PE-MPs on Brassica rapa, which is a typical model plant and only have around a 30-day life cycle. It is noted that the presence of photodegraded PE-MPs inhibited Brassica rapa growth since the stem length decreased by 11.94%-51.11% while the fresh weight and dry weight decreased by 18.56%-27.46% and 1.90% -6.91% respectively, compared to the blank group. PE-MPs receiving more light radiation became more hydrophobic. This inhibited PE-MPs entering the plant body along with the process of plant absorbing water. Furthermore, when PE-MPs were located in the lower soil layers, Brassica rapa reaching them needs a longer time, hence showing lower toxicity effect than the case of PE-MPs located in the upper soil layer. The research outcomes also indicated that malondialdehyde (MDA) contents in photodegraded PE-MPs exposure group increased by 1.37%-7.28% while the catalase activity (CAT) increased by 60.11%. This means that PE-MPs caused oxidative stress response in plants, inducing plants to resist external stress. Transcriptomic analysis results showed that Brassica rapa, which was affected by PE-MPs, significantly up-regulated genes related to the plant-pathogen interaction pathway while the ribosome pathway genes were significantly down-regulated. This led to a decrease in growth rate and a decrease in the homeostatic level of the ribosomal subunit and hence resulting in abnormal leaf vein development. These conclusions indicated the toxic effect and damage mechanism of photodegraded PE-MPs on Brassica rapa. The novelty of this study was to use both univariate analysis and transcriptomic analysis to investigate how photodegraded PE-MPs exert toxicity on Brassica rapa. The results can provide a theoretical basis for revealing the influence of MPs on plant growth.