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The effect of microplastics on root growth and on mitotic cell division in onion
Summary
This study investigated how microplastics affect root growth and cell division in onion (Allium cepa), a standard model organism for plant toxicology testing. The results help evaluate whether microplastic exposure in soil can impair plant growth, which is relevant to understanding agricultural risks from microplastic-contaminated soils.
Pollution of the freshwater and terrestrial environment with microplastics is a major problem. Nowadays, there is still a lack of knowledge about how microplastics affect plants. With the onion test, we wanted to determine whether the onions (Allium cepa) that grow in the microplastic suspension have a smaller number and length of the roots, as well as whether the frequency of cell division in the roots is smaller and the number of mitotic aberrations is greater than in control group onions, which were grown in distilled water. We also wanted to find out the difference in the inhibitory effect of two types of microplastic, namely, microplastics isolated from the cosmetic product and untreated microplastics, and whether the result is influenced by the age of the bulbs. For this purpose, we grew onions in two independent experiments for 24 hours and 5 days in microplastic suspensions, and after the experiment was completed, we counted and measured onion roots and prepared squeezed preparations of root tips, which were examined under a microscope. We found that the microplastic suspension in which the bulbs were grown did not cause a statistically significant reduction in the number and length of the roots and did not significantly reduce the value of the mitotic index. Chromosomal aberrations were more frequent in onions grown in microplastic suspensions, but differences in effects between different types of microplastic were not statistically significant. We also found that the age of the bulbs has a marked influence on the result. For elderly bulbs with less stagnant substances, root growth and mitotic index in control groups were worse than in younger bulbs with several stagnant substances. The older control bulbs also had a higher proportion of control in older chromosome aberrations, and consequently a higher influence of microplastic in the suspension was observed in this group. Therefore, we suggest that the same old bulbs are used in the tests.