Combined Application of 2,4-Epibrassinolide and K₂SO₄ Improved the Cadmium Tolerance in Tobaccos by Protecting Chloroplast and Reducing Cd Accumulation

Potassium sulfate (K₂SO₄) or 2,4-Epibrassinolide (EBL) mediated response to cadmium (Cd) stress in plants has been widely reported, but the joint effect both on plants in response to Cd stress remains obscure. Herein, our results showed the combined application of K₂SO₄ (10 mM) and EBL (0.2 μM) on tobacco plants under Cd stress (CdCl₂, 100 μM) relieved Cd toxicity by improving the activities of AOEs and reducing the contents of decreasing superoxide (H₂O₂ and O₂⁻) and cadmium ion. As a result, the synergetic application of K₂SO₄ and EBL protected the integrity of chloroplast, which ensured a normal process of photosynthesis without a significant decrease in photosynthetic pigment content. Additionally, the combined application of K₂SO₄ and EBL also inhibited the expression of the Cd transport-related gene NtNramp1 and enhanced the Cd efflux-related gene NtHMA2. Moreover, the combined treatment of EBL associated with K₂SO₄ also effectively reduced the Cd accumulation in tobacco leaves under Cd stress compared with the groups treated separately, which implied a potentially synergistic role of EBL and K₂SO₄ in alleviating Cd toxicity in tobacco plants. This study provides a theoretical reference for the further analysis of the molecular mechanism of K₂SO₄ and EBL in jointly mediating the response to heavy metals in plants.