Experimental assessment of radioprotective efficiency of Rhizoplaca chrysoleuca (Sm.) Zopf extract against uranyl nitrate hexahydrate

Uranium is a radiotoxic heavy metal capable of causing severe biochemical and genetic disturbances in living organisms through both chemical toxicity and ionizing radiation. Due to increasing concerns about uranium exposure from nuclear industries and environmental contamination, the search for natural compounds with radioprotective properties has gained significant momentum. This study investigates the protective effects of Rhizoplaca chrysoleuca (Sm.) Zopf. lichen extract against the multi-faceted toxicity induced by uranyl nitrate hexahydrate (UNH) in Allium cepa L., a well-established model for environmental toxicity testing. A. cepa bulbs were exposed to 50 mg/L UNH alone and in combination with two concentrations of the lichen extract (0.5 g/L, and 1.0 g/L) for 72 h. Physiological endpoints such as germination rate, root length, and weight gain were assessed alongside cytogenetic markers including mitotic index, micronucleus frequency, chromosomal aberrations and DNA fragmentation (assessed by the Comet assay). Biochemical stress responses were evaluated through measurements of malondialdehyde, proline accumulation, antioxidant enzyme activities (superoxide dismutase and catalase), and chlorophyll a and b contents. Additionally, the phenolic composition of the extract was characterized by LC-MS/MS to identify protective bioactive compounds. Statistical analyses were performed using one-way ANOVA followed by Duncan’s test (p < 0.05). Uranyl nitrate hexahydrate exposure led to pronounced reductions in growth parameters, elevated oxidative stress biomarkers, extensive chromosomal abnormalities, and DNA fragmentation, confirming its high genotoxic and cytotoxic potential. However, co-treatment with R. chrysoleuca extract significantly mitigated these toxic effects in a concentration-dependent manner, restoring mitotic activity, reducing oxidative stress, and preserving cell structure and DNA integrity. LC-MS/MS analysis revealed high levels of phenolic compounds such as cinnamic acid, protocatechuic acid, and vanillin, which are known for their antioxidant and DNA-protective properties. These results highlight the potential of R. chrysoleuca as a bioresource for the development of plant-based radioprotective agents and highlight its applicability in environmental remediation and phytomedicine aimed at mitigating heavy metal-induced toxicity.