Microspatial distribution and multi-omics insights into root Nickel accumulation and tolerance in Leersia hexandra Swartz.

Nickel (Ni) contamination has become an increasingly important environmental issue, and phytoremediation is considered a sustainable strategy for its remediation. Leersia hexandra Swartz shows strong tolerance to multiple heavy metals, yet the mechanisms underlying its root response to Ni stress remain poorly understood. In this study, L. hexandra was exposed to Ni concentration gradient treatments, followed by inhibitor assays, synchrotron-based microspatial imaging, and integrated root transcriptomic and metabolomic analyses of roots to investigate its root-level responses to Ni stress. Ni accumulation in L. hexandra increased with external Ni concentration, with roots serving as the predominant site of Ni retention. Inhibitor assays showed that TEA and metabolic inhibitors significantly reduced root Ni accumulation in root, suggesting that root Ni accumulation may be associated with energy-dependent processes and TEA-sensitive cation transport systems. Microspatial imaging revealed strong Ni signals in the root apex and stele, indicating a heterogeneous spatial distribution of Ni and its potential radial movement within root tissues. Integrated multi-omics analyses nidicated that short-term Ni exposure was mainly associated with changes in transport regulation, signal transduction, and antioxidant defense, whereas prolonged exposure was characterized by sustained regulation of transporter-related genes, metabolic reprogramming, and changes in hormone-related pathways. These results indicate that Ni tolerance in L. hexandra is closely associated with a coordinated root-based strategy involving Ni uptake, redistribution, retention, and metabolic buffering. This study provides a mechanistic basis for understanding Ni tolerance in wetland accumulator plants and for the application of L. hexandra in phytoremediation of Ni-contaminated environments.