Influence of β-radiation dose rate on induced cytogenetic endpoints in Allium cepa cells

Ionizing radiation induces DNA damage, often resulting in mutations or cell death. The micronucleus (MN) assay in Allium cepa has become a gold standard for evaluating radiation-induced genomic damage. This study investigates the effects of beta radiation on Allium cepa root meristem cells by analyzing MN formation and the mitotic index (MI) at varying absorbed doses (0.72 Gy, 2 Gy, and 4 Gy) and dose rates (D˙₁ = 7.2 mGy/s, D˙₂ = 13.8 mGy/s, and D˙₃ = 19.5 mGy/s) using a homemade irradiator (Samara) with calibrated ⁹⁰Sr+⁹⁰Y sources. A control group was included for comparison. After irradiation, roots were fixed in Carnoy's solution, stained with acetic orcein, and analyzed under a microscope. MN frequency was determined by scoring 1000 interphase cells per root, and MI was calculated. Statistical analysis was performed using ANOVA and Tukey's test (p < 0.05). At the lowest dose rate (D˙₁), MN frequency increased in a dose-dependent manner, predominantly with cells containing a single MN. A similar trend was observed at the highest dose rate (D˙₃), with cells maintaining mitotic activity despite radiation-induced damage. At the intermediate dose rate (D˙₂), MN frequency decreased at higher doses, likely due to increased cell death. The study underscores the importance of considering both dose rate and MI in radiation dosimetry using Allium cepa, as higher doses at certain dose rates may lead to increased cell death, potentially underestimating radiation-induced damage.