Salt-tolerance induced by leaf spraying with H2O2 in sunflower is related to the ion homeostasis balance and reduction of oxidative damage

Salinity is still one of the main factors that limit the growth and production of crops. However, currently, hydrogen peroxide (H2O2) priming has become a promising technique to alleviate the deleterious effects caused by salt. Therefore, this study aimed to test different leaf spraying strategies with H2O2 for acclimation of sunflower plants to salt stress, identifying the main physiological and biochemical changes involved in this process. The experiment was conducted in a completely randomized design, with four replications. Initially, four concentrations of H2O2 were tested (0.1; 1; 10 and 100 mM) associated with different applications: 1AP - one application (48 h before exposure to NaCl); 2AP - two applications (1AP + one application 7 days after exposure to NaCl) and 3AP - three applications (2AP + one application 14 days after exposure to NaCl), besides this two reference treatments were also added: control (absence of NaCl and absence of H2O2) and salt control (presence of 100 mM of NaCl and absence of H2O2). The experiment was conducted in hydroponic system containing Furlani's nutrient solution. Salt stress reduced the growth of sunflower plants, however, the H2O2 priming through leaf spraying was able to reduce the deleterious effects caused by salt, especially in the 1 mM H2O2 treatment with one application. H2O2 acts as a metabolic signal assisting in the maintenance of ionic and redox homeostasis, and consequently increasing the tolerance of plants to salt stress.