Differential cellular and DNA damage responses of meristematic cells to trace and excess Selenium exposure

Selenium (Se) is an element that can be beneficial to plants in trace amounts, but can exhibit toxicity beyond these trace amounts. This study aimed to determine the dose-dependent toxic effects of different Se doses on Allium cepa meristem cells; cytogenetic, anatomical, biochemical, and physiological changes were evaluated using a holistic approach. For this purpose, Allium bulbs were exposed to Se concentrations of 1.5, 3, 10, 20, and 50 µM. Genotoxicity was assessed using the mitotic index, micronucleus frequency, chromosomal abnormalities, and comet test; oxidative stress indicators, as well as anatomical and physiomorphological changes, were also analyzed. The findings revealed that Se exhibits a significant dose-response relationship in A. cepa cells. Low doses of Se (1.5-3 µM) did not produce genotoxic effects; cell division and DNA integrity were preserved at these doses. In contrast, at doses of 10 µM and above, the mitotic index decreased significantly, while micronucleus formation, chromosomal abnormalities, and DNA damage increased significantly. Comet analysis results showed sharp increases in tail DNA percentage, tail length, and tail moment, and advanced DNA fragmentation occurred, especially at 20 and 50 µM Se applications. The observed genotoxic effects are accompanied by oxidative stress, characterized by increased lipid peroxidation, decreased reduced glutathione levels, and increased antioxidant enzyme activities. Anatomical studies also confirmed that structural damage in the root meristem tissue increased in a dose-dependent manner at high doses of Se. All these negative effects also caused regression in physiological development. In conclusion, this study clearly demonstrates that Se does not exhibit genotoxic effects at low doses in Allium cepa meristem cells, but causes severe genotoxicity and DNA damage above a certain threshold. The findings highlight that dose is a critical determinant in Se applications in plants and contribute to the understanding of Se-induced genetic damage mechanisms.