Cytotoxic Effects of Ethidium Bromide on Onion (Allium cepa) Root Meristem Cells
DOI:
https://doi.org/10.67601/njbls.v3i2b.70Keywords:
Ethidium bromide, Allium cepa, Cytogenetic bioassay, Cells, Concentrations, Chromosomal aberrationsAbstract
Ethidium bromide (EtBr) is a widely used nucleic acid-intercalating dye with well-documented mutagenic potential, yet its cytogenetic effects on plant model systems remain poorly characterised. This study evaluated the cytotoxic effects of EtBr on Allium cepa root meristem cells using the Allium bioassay. Uniformly graded onion bulbs were exposed for ten days to five graded concentrations of EtBr (2–10 µL of stock solution per 100 mL distilled water) alongside an untreated control, after which root tips were fixed, hydrolysed and stained for microscopic examination. Germination rate was highest in control (4.67±1.80) and progressively decline as EtBr increases with the least observed in 10 µL (0.20±1.80), and the total mean value of roots growth was highest in control (4.67±1.80) while the least was observed in 10 µL (0.20±1.80). The control of the mitotic phase distribution had 14 dividing cells and normal cells in all the phases of 2.80±0.83, with zero abnormal cells, while the number of abnormal cells increases and normal cells declined as EtBr concentration increase, and at 10 µL EtBr (0.00±0.00), there was zero normal cells observed. The frequency of chromosomal aberrations (CAs) was more pronounced in 10 µL EtBr (42), while in the control and 2 µL EtBr had little to no chromosomal aberrations (2 and 6 respectively). EtBr produced a concentration-dependent decline in both root traits and mitotic phase distribution, indicating suppressed cell proliferation. Chromosomal aberrations, including fragmented chromosomes, multinucleated cells, sticky prophase and metaphase, bridges in anaphase, and abnormalities in metaphase during the various mitotic phases, rose significantly with increasing dosage of EtBr, and the highest concentration tested produced the most pronounced clastogenic damage. These findings confirmed that EtBr is cytotoxic to A. cepa root cells, underscore the environmental risk posed by the handling and release of EtBr as laboratory effluent, and support the continued use of the Allium cepa assay as a sensitive, low-cost bioindicator for chromosome-damaging agents.
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