Exclusion versus Detoxification: Contrasting Molecular Strategies of Aluminium Tolerance in Rice Landraces of Northeast India

Aluminium (Al) toxicity affects rice cultivation in acidic soils, largely by hindering root development and diminishing crop yield. This study investigated 53 rice genotypes from Northeast India under hydroponic conditions to assess their morpho-physiological and molecular responses to aluminium stress. Nine characteristics, including as root length, root tolerance index, relative root elongation, and biomass, were measured to categorise genotypes into tolerant, moderately tolerant, intermediate, moderately susceptible, and susceptible classifications. Root characteristics proved to be the most sensitive predictors of tolerance, with cluster and principal component analyses reliably distinguishing tolerant from susceptible genotypes. SSR marker study (33 polymorphic markers, 103 alleles, mean PIC = 0.48) indicated substantial genetic variety, although did not entirely align with phenotypic grouping. Gene expression profiling revealed divergent molecular strategies: tolerant genotypes upregulated OsSTAR1, OsSTAR2, and OsFRDL4, facilitating aluminium exclusion through cell wall modification and citrate efflux, whereas susceptible genotypes demonstrated increased expression of OsNRAT1 and OsALS1, indicating dependence on internal sequestration. These findings highlight root-based exclusion mechanisms as the principal factor influencing Al tolerance in rice.