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

Abstract

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.

Keywords: Agricultural water management; Crop biomass; Crop production; Cross-talk; H2O2; Helianthus annuus L.; Oxidative stress; Physiological parameters; Plant growth; Plant physiology; Salinity.

Figure 1

Effect of salt stress (100 mM NaCl) and leaf spraying with H₂O₂ (1 mM H₂O₂ 1AP^∗) on the shoot dry mass (ShDM) (at 21 and 35 days) (A) and on the net CO₂ assimilation rate (P_N) (at 35 days) (B) of sunflower plants grown in nutrient solution. Means of four repetitions ±standard error. Means followed by the same letters, on each date, do not differ statistically from each other, using the Tukey's test (p ≤ 0.05). ^∗1AP - one application by leaf spraying 48 h before exposure to NaCl.

Figure 2

Effect of salt stress (100 mM NaCl) and leaf spraying with H₂O₂ (1 mM H₂O₂ 1AP^∗) on the content of chlorophyll a (Chl a) (A), chlorophyll b (Chl b) (B), chlorophyll a + b (Chl a + b) (C) and carotenoids (Car) (D) of sunflower plants grown in nutrient solution, at 21 and 35 days. Means of four repetitions ±standard error. Means followed by the same letters, on each date, do not differ statistically from each other, using the Tukey's test (p ≤ 0.05). ^∗1AP - one application by leaf spraying 48 h before exposure to NaCl.

Figure 3

Effect of salt stress (100 mM NaCl) and leaf spraying with H₂O₂ (1 mM H₂O₂ 1AP^∗) on the relative water content (RWC) (A), electrolyte leakage (EL) (B), water saturation deficit (WSD) (C), water content at saturation (WCS) (D), leaf succulence (SUC) (E) and sclerophylly index (SI) (F) of the leaves of sunflower plants grown in nutrient solution, at 21 and 35 days. Means of four repetitions ±standard error. Means followed by the same letters, on each date, do not differ statistically from each other, using the Tukey's test (p ≤ 0.05). ^∗1AP - one application by leaf spraying 48 h before exposure to NaCl.

Figure 4

Effect of salt stress (100 mM NaCl) and leaf spraying with H₂O₂ (1 mM H₂O₂ 1AP^∗) on the contents of Na⁺ (A and B), K⁺ (C and D), Cl⁻ (E and F) in leaves and roots, respectively, of sunflower plants grown in nutrient solution, at 21 and 35 days. Means of four repetitions ±standard error. Means followed by the same letters, on each date, do not differ statistically from each other, using the Tukey's test (p ≤ 0.05). ^∗1AP - one application by leaf spraying 48 h before exposure to NaCl.

Figure 5

Effect of salt stress (100 mM NaCl) and leaf spraying with H₂O₂ (1 mM H₂O₂ 1AP^∗) on the levels of soluble carbohydrates (A and B), free amino acids (C and D), free proline (E and F), and soluble proteins (G and H) in leaves and roots, respectively, of sunflower plants grown in nutrient solution, at 21 and 35 days. Means of four repetitions ±standard error. Means followed by the same letters, on each date, do not differ statistically from each other, using the Tukey's test (p ≤ 0.05). ^∗1AP - one application by leaf spraying 48 h before exposure to NaCl.

Figure 6

Effect of salt stress (100 mM NaCl) and leaf spraying with H₂O₂ (1 mM H₂O₂ 1AP^∗) on the activity of ascorbate peroxidase (APX) (A and B), catalase (CAT) (C and D), superoxide dismutase (SOD) (E and F), and lipid peroxidation (LP) (G and H) in leaves and roots, respectively, of sunflower plants grown in nutrient solution, at 21 and 35 days. Means of four repetitions ±standard error. Means followed by the same letters, on each date, do not differ statistically from each other, using the Tukey's test (p ≤ 0.05). ^∗1AP - one application by leaf spraying 48 h before exposure to NaCl.