Revealing the mechanistic basis of differential salt-induced oxidative stress tolerance between Oryza sativa and Oryza coarctata

Oryza coarctata is the only halophytic relative in the genus Oryza ( Oryza sp.) that is tolerant to high salinity levels lethal to cultivated rice varieties. An excessive accumulation of reactive oxygen species (ROS) caused by salinity leads to oxidative stress, although certain ROS also play important signaling roles. This work investigated differences in root redox and ionic homeostasis between cultivated ( O. sativa ) and wild ( O. coarctata ) rice species. Root treatment with 10 mM H₂O₂ decreased cell viability in cultivated but not wild rice, and histochemical staining showed greater H₂O₂ accumulation in wild rice roots under non-saline conditions, suggesting a signaling role. Wild rice showed higher superoxide dismutase (SOD) activity that lowers superoxide (O₂^-) accumulation. Cultivated rice showed greater K⁺ loss from the root mature zone through ROS-activated cation channels accompanied by stronger Ca²⁺ uptake in response to H₂O₂ application, while wild rice possessed better Ca²⁺ homeostasis with less H₂O₂-induced K⁺ leakage. Cultivated rice also demonstrated much higher sensitivity to hydroxyl radicals (^●OH). Wild rice effectively controlled cytosolic Ca²⁺ homeostasis by Ca²⁺ efflux systems such as Ca²⁺-ATPase and CAX, while cultivated rice downregulated RBOH expression that may affect operation of the “ROS-Ca²⁺ hub” and signaling cascades under salinity.