Gamma irradiation-induced metabolic reprogramming as a determinant of radiation tolerance in thai rice germplasm for space agriculture

Abstract Radiation beyond Earth’s atmosphere poses a major challenge for space agriculture by affecting seed viability and plant establishment. As a controllable terrestrial analogue of cosmic radiation, gamma (γ) irradiation provides a practical model for evaluating crop resilience. Although rice ( Oryza sativa ) is a promising space crop candidate, germination alone does not ensure developmental or metabolic stability under irradiation stress. Here, eight Thai rice cultivars were screened for radiation tolerance based on early seedling performance following γ-irradiation at 150, 300, and 900 Gy. All cultivars retained high germination capacity (> 90%) across all doses, whereas shoot and root elongation exhibited clear dose-dependent inhibition, with root growth showing greater sensitivity. Based on relative growth maintenance, cultivar 248HT was identified as the most γ-radiation tolerant genotype and selected for in-depth analysis. Untargeted metabolomics of roots and shoots revealed pronounced, tissue-specific metabolic reprogramming in response to irradiation. Roots displayed strong upregulation of metabolites associated with redox homeostasis, including NAD⁺ salvage intermediates and glutathione-related compounds, alongside suppression of nitrogen- and nucleotide-intensive pathways. Targeted phytohormone profiling further demonstrated a consistent reduction in gibberellic acid (GA₃) and accumulation of abscisic acid (ABA), resulting in a lowered GA₃:ABA ratio that aligned with reduced elongation growth. Collectively, these results indicate that radiation tolerance in rice is underpinned by coordinated hormonal recalibration and metabolic shifts that prioritise oxidative stress mitigation, DNA repair, and controlled growth. The superior performance of 248HT highlights it as a promising candidate for further space related radiation stress studies and provides metabolomic markers for selecting or engineering radiation-resilient rice varieties.