Radio-tolerance of finger millet Eleusine coracana (L.) Gaertn cultivars to ionizing radiation

In the current study, the basis of differential radio-tolerance to γ-irradiation of two cultivars of finger millet, Eleusine coracana (L.) Gaertn was established as assayed from their genotoxicity and oxidative stress responses. Seeds of E. coracana cultivars, cv. Bhairabi and cv. Suvra, were γ-irradiated at doses in the range 0–2.5 kGy. The mitotic index and frequency of chromosomal aberrations and micronuclei in root meristem cells of germinating seeds were determined. The formation of reactive oxygen species (ROS: H₂O₂, O₂ •⁻, •OH), cell death, lipid peroxidation, activities of antioxidant enzymes: catalase, superoxide dismutase, guaiacol peroxidase, ascorbate peroxidase and glutathione reductase, levels of chlorophyll a and b, carotenoids, and total phenols, and the ROS-scavenging ability were determined in the leaves of six-day old seedlings. γ-Irradiation of seeds, in a dose-dependent fashion, significantly inhibited seedling growth and induced genotoxicity in the root meristem cells, and induced formation of ROS, cell death, lipid peroxidation, activation of antioxidant enzymes, and depleted photosynthetic pigments, phenols, and free radical scavengers in the leaf tissue. The threshold doses determined on the basis of lethal dose hundred (LD₁₀₀) and dose fifty (D₅₀) on the basis of seedling growth, the highest ineffective threshold dose (HITD) and the lowest effective threshold dose (LETD) on the basis of genotoxicity established higher radio-tolerance in cv. Bhairabi (LD₁₀₀ = 2.0, D₅₀ = 1.01, HITD =0.075, LETD =0.1 kGy) compared to cv. Suvra (LD₁₀₀ = 1.0, D₅₀ = 0.38, HITD =0.025, LETD =0.05 kGy). The genotoxicity assay validated the non-linear threshold (NLT) dose-response to γ-irradiation as opposed to the prevailing linear no-threshold (LNT) dose-response concept. The antioxidant response to γ-irradiation was correspondingly more pronounced in seedlings of the cv. Bhairavi than cv. Suvra. The differential radio-tolerance of the E. coracana cultivars appeared to be due to the differences in their antioxidative potentials.