Selenium increases the capacity of antioxidative defense and their accompanying metal cofactors in maize under sulfate salinity

• Selenium demonstrates a protective and antioxidative role under Cl − and SO 4 2− salinity. • Moderate selenium supply under high SO 4 2− availability increases the absorption of metal cofactors. • Moderate selenium level under SO 4 2− salinity reduces ROS toxicity by enhancing the enzymatic machinery inside the salt-affected plants. The most prevalent salts in saline soils are sodium salts like NaCl and Na 2 SO 4 . Various salinity forms are the most harmful abiotic stress, which can affect plants' growth, uptake of nutrients, and antioxidant machinery. Selenium (Se) confers resistance to salinity by stimulating the ROS detoxification, which are over-accumulated due to stress. Three doses of Se (0, 10, and 50 µM) were applied to hydroponically grown maize under both Cl − and SO 4 2− -salinity at an equimolar Na + concentration of 100 mM to evaluate the impact of Se on important enzyme activities and nutrient uptake. Higher levels of MDA content under Cl − -salinity were associated with higher levels of oxidative stress in plants, demonstrating that Cl − -salinity has more harmful effects than SO 4 2− -salinity. Se application considerably increased the Se concentration in plant tissues, but SO 4 2− -salinity caused less absorption due to competition. Compared to Se-free shoots, moderate Se dramatically increased the levels of metals, including Zn, Mn, Fe, and Cu, essential for enzyme function under SO 4 2− -salinity conditions. In contrast, no significant effects were observed under Cl − -salinity conditions. Se at a moderate level promoted antioxidant capacity by significantly inducing the enzymatic activities (APX, CAT, GR, SOD, and GPX) in similar patterns under the SO 4 2− -salinity condition. Whereas, compared to Se0, moderate Se level elevated SOD, CAT, and GPX activities under Cl − -salinity, indicating Se's protective and antioxidative role under salinity. The results suggest that even with low uptake due to high SO 4 2− availability, moderate Se supply increases the absorption of metal cofactors (micronutrients). This, in turn, enhances antioxidative defenses, enabling maize crops to better tolerate salt stress.