Standardization of the <i>Allium cepa</i> assay: a useful tool in the genotoxic evaluation of plant extracts

BACKGROUND: The Allium cepa (onion) test is a sensitive tool for genotoxicity studies used worldwide to assess environmental contamination and potential toxicity of natural products. OBJECTIVES: To standardize and validate the experimental parameters of the Allium cepa assay and apply the standardized protocol to six ethanolic plant extracts from the Colombian Caribbean flora. METHODS: Key experimental variables were systematically evaluated: onion supplier, type of onion, environmental conditions, stimulation phase, water replacement, type of water, and Cd+2 concentration as positive control. Genotoxicity was assessed through the mitotic index (MI) and aberration index (AI) in root meristems. RESULTS: The optimal conditions were white onions from chain store P2, bottled drinking water with total replacement every 24 h, 24±1°C with indirect fluorescent lighting, a 72-h stimulation phase, nine onions per concentration, a 72-h exposure phase, and Cd+2 at 5 mg/L as positive control. Under these conditions, ethanolic extracts of Chenopodium ambrosioides, Momordica charantia, and Tabebuia ochracea induced significant genotoxic effects, whereas Crescentia cujete, Cordia dentata, and Heliotropium indicum showed no adverse effects. CONCLUSIONS: A reproducible and validated protocol was obtained for the Allium cepa genotoxicity assay. Its application revealed significant genotoxic activity in C. ambrosioides, M. charantia, and T. ochracea, as evidenced by decreased MI and increased AI, underscoring the need for further toxicological assessment of these species.