Interactive role of epibrassinolide and hydrogen peroxide in regulating stomatal physiology, root morphology, photosynthetic and growth traits in Solanum lycopersicum L. under nickel stress

Nickel (Ni) is a fundamental component that assumes a vital role in managing plant growth and development. Its acquisition in soil is presently viewed as a consequential ecological issue imperilling crop productivity globally. Brassinosteroid and low concentration of H2O2 as signalling molecule could modify stomatal movement, root morphology, photosynthetic effectiveness and generation of antioxidants and finally growth traits to make the tomato plants more tolerant to Ni stress. Therefore, a study was conducted to study the effect of exogenously applied epibrassinolide (EBL; foliar spray) and H2O2 (root dipping) to nickel (Ni) stressed plants. EBL and H2O2 applied through different modes modified stomatal movement, root morphology, photosynthetic effectiveness and growth traits of Solanum lycopersicum L. plants grown under stress free and surplus Ni. The increased Ni- tolerance of tomato plants caused by EBL and H2O2 could be attributed to its capability to restrict Ni uptake, reduce Ni- inflicted oxidative burst as illustrated by lower levels of hydrogen peroxide, superoxide and electrolyte leakage in Ni- stressed plants. In addition, EBL and H2O2 increased the antioxidant capability in Ni stressed plants by sustaining increased activities of enzymes for ROS-detoxification, particularly catalase (CAT), guaiacol peroxidase (GPOX) and superoxide dismutase (SOD) and proline accumulation. These improved activities of antioxidant enzymes and accumulation of proline (osmolyte) elicited by the blend of EBL and H2O2, would have retained the ability to confer resilience to Solanum lycopersicum plants exposed to higher doses of Ni. This study further affirms that the combined application of EBL and H2O2 in various ways proved very effective to ameliorate the effects of Ni toxicity in tomato plants through modification of stomatal movement, root morphology, photosynthetic effectiveness and growth traits.