Wheat roots adapt to potassium deficiency through coordinated antioxidant, hormonal, and metabolic reprogramming: Insight from morpho-physiological, biochemical, and transcriptomic analysis

• Low-K⁺ remodels root hierarchy • Low-K⁺ activates antioxidant-phytohormone responses and carbon metabolic reprogramming • Physiological-transcriptomic reveal ROS-hormone-K⁺ transporter network interplay in low-K⁺ • 0.1 μM NAA rescues low-K⁺ stress by synergizing root remodeling and K⁺ uptake efficiency Potassium (K) deficiency poses a significant threat to global wheat production, yet comprehensive investigations integrating physiological and transcriptomic responses to K-deficiency stress in wheat remain critically underexplored. This study investigated the physiological, biochemical, and transcriptomic adaptations of wheat under low-K conditions (0.01 mM K⁺) compared with a sufficient-K control (6 mM K⁺). Low-K stress severely inhibited plant growth, reducing shoot and root biomass by 37%-60% and 42%-64%, respectively, and impairing root morphology through decreases in root length, surface area, and tip number. Photosynthetic performance was also compromised, with significant reductions in chlorophyll content (6%-31%), stomatal conductance (37%-56%), and photosynthetic rate (17%-39%). Antioxidant defense systems were activated under K deficiency, as evidenced by elevated malondialdehyde (MDA) levels and increased activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX), alongside upregulated glutathione (GSH) and ascorbate (AsA) biosynthesis. Transcriptomic analysis identified 14,566 differentially expressed genes (DEGs) enriched in pathways including phenylpropanoid biosynthesis, plant hormone signaling, and glutathione metabolism. Key K⁺ transporters (HAK, HKT, AKT1) and calcium signaling components (CBLs, CIPKs) were strongly induced, suggesting central roles in K⁺ acquisition and stress adaptation. In addition, K deficiency promoted the accumulation of phytohormones (IAA, ABA, CTK, BR), which correlated with transcriptional activation of auxin- and ABA-responsive genes. Concurrently, exogenous application of auxin at specific concentrations mediates low-K⁺ stress alleviation through enhanced potassium uptake efficiency and root architectural remodeling. These findings reveal integrated physiological and molecular strategies that enable wheat to mitigate K deficiency, highlighting potential targets for breeding K-efficient cultivars to enhance sustainable wheat production.