Root iron sequestration and antioxidant regulation govern iron-toxicity tolerance in indigenous rice genotypes from Northeast India.

key messageRice genotypes exhibit differential iron-toxicity tolerance, where tolerant types maintain iron homeostasis through plaque formation, sequestration and antioxidant defense, while sensitive genotypes accumulate excess iron, causing oxidative damage and cellular dysfunction. Iron (Fe) toxicity is a major constraint to rice production in waterlogged acidic soils, where excessive accumulation of ferrous iron disrupts cellular homeostasis and limits crop productivity. Indigenous rice germplasm represents a valuable source of adaptive traits for improving stress tolerance; however, the mechanisms underlying Fe toxicity tolerance in traditional rice cultivars from Northeast India remain poorly understood. In this study, 55 indigenous rice genotypes from Assam were evaluated under hydroponic iron stress to identify physiological, biochemical, and molecular traits associated with tolerance. Considerable genotypic variation was observed in germination, seedling growth, biomass retention, root and shoot tolerance indices, and leaf bronzing symptoms. Tolerant genotypes, including Ahom Sali, Phul Pakhori, Prasad Bhog, and Mahsuri, maintained higher biomass, lower leaf bronzing, enhanced root iron plaque formation, restricted iron translocation to shoots, and greater antioxidant enzyme activities than susceptible genotypes. These responses were associated with reduced oxidative damage and improved maintenance of nutrient homeostasis under excess iron conditions. Gene expression analysis performed in one representative tolerant genotype (Ahom Sali) and one susceptible genotype (Ranjit Sub-1) revealed differential regulation of OsFer1, OsVIT2, OsIRT1, and OsFeSOD2, providing preliminary evidence that iron sequestration and antioxidant defense contribute to Fe toxicity tolerance. Overall, the study demonstrates that coordinated regulation of root iron sequestration, intracellular iron storage, and antioxidant defense underpins Fe toxicity tolerance in indigenous rice. The identified tolerant genotypes represent valuable genetic resources for developing Fe toxicity-resilient rice cultivars adapted to acid soil ecosystems.