Thiourea and hydrogen peroxide priming improved K⁺ retention and source-sink relationship for mitigating salt stress...

Plant bioregulators (PBRs) represent low-cost chemicals for boosting plant defense, especially under stress conditions. In the present study, redox based PBRs such as thiourea (TU; a non-physiological thiol-based ROS scavenger) and hydrogen peroxide (H₂O₂; a prevalent biological ROS) were assessed for their ability to mitigate NaCl stress in rice variety IR 64. Despite their contrasting redox chemistry, TU or H₂O₂ supplementation under NaCl [NaCl + TU (NT) or NaCl + H₂O₂ (NH)] generated a reducing redox environment in planta, which improved the plant growth compared with those of NaCl alone treatment. This was concomitant with better K⁺ retention and upregulated expression of NaCl defense related genes including HAK21, LEA1, TSPO and EN20 in both NT and NH treated seedlings. Under field conditions, foliar applications of TU and H₂O₂, at vegetative growth, pre-flowering and grain filling stages, increased growth and yield attributes under both control and NaCl stress conditions. Principal component analysis revealed glutathione reductase dependent reduced ROS accumulation in source (flag leaves) and sucrose synthase mediated sucrose catabolism in sink (developing inflorescence), as the key variables associated with NT and NH mediated effects, respectively. In addition, photosystem-II efficiency, K⁺ retention and source-sink relationship were also improved in TU and H₂O₂ treated plants. Taken together, our study highlights that reducing redox environment acts as a central regulator of plant's tolerance responses to salt stress. In addition, TU and H₂O₂ are proposed as potential redox-based PBRs for boosting rice productivity under the realistic field conditions.