Interactive effect of selenium and sulfur on micronutrient uptake, together with zinc transporters expression, and antioxidant enzymes under sulfate salinity in crop plants

A set of three separate experiments was conducted to assess the interaction between Se and S in plants, with a primary focus on promoting micronutrient translocation and uptake, improving nutritional quality, and protecting against oxidative damage under salinity stress. Our findings indicated that under S deficiency, foliar Se negatively affects the levels of vital micronutrients in spinach. However, at the modest Se level (0.5 µM) and the sufficient S level (1 mM) or high S level (5 mM) exerts a synergistic influence on micronutrients (including Se) uptake in spinach. In addition, moderate Se in S availability at adequate or high levels also promoted the accumulation of proteins, water-soluble sugars, and organic acids, thereby improving the nutritional status and food quality of vegetables, such as spinach. In the second study, our findings indicated that Se at moderate level (10 µM) significantly induces the activity of antioxidant enzymes such as GPX, CAT, and SOD in maize plants exposed to NaCl. Moreover, a similar moderate Se level markedly enhanced the activities of the all studied antioxidant enzymes (APX, GR, GPX, CAT, and SOD) in plants under Na₂SO₄ salinization. The notable increase in Zn, Mn, Fe, and Cu by Se moderate level was observed under Na₂SO₄ salt form, which acts as cofactors for abovementioned enzymes, thus suggesting the beneficial role of Se in boosting defense mechansim, in order to resist abiotic stress. In third study, our findings revealed that the transcript levels of genes ZIP2, ZIP4, ZIP5, ZIP1, and HMA3 were strongly induced by Se supplementation (10 µM) in sulfate-salinized plants compared with their counterparts in non-saline plants. However, in the absence of Se, no substantial variation in the transcript abundance was noticed in similarly treated plants. This very trend was observed in micronutrient concentrations in xylem sap and in nutrient concentrations in roots under sulfate-salinity. This suggests that Se at the moderate level (10 µM) strongly promotes the expression of metal transporters, such as ZIP gene transporters and heavy metal ATPases, thereby enabling plants to translocate and uptake the crucial micronutrients (Zn, Mn, Fe, and Cu) under sulfate salinity conditions.