Synergistic Effects of Salicylic Acid and Melatonin on Modulating Ion Homeostasis in Salt-Stressed Wheat (Triticum aestivum L.) Plants by Enhancing Root H+-Pump Activity

Abstract

Salicylic acid (SA) and melatonin (MT) have been shown to play important roles in plant salt tolerance. However, the underlying mechanisms of SA-MT-interaction-mediated ionic homeostasis in salt-stressed plants are unknown. As a first investigation, this study aimed to clarify how SA-MT interaction affects H⁺-pump activity in maintaining the desired ion homeostasis under saline conditions and its relation to ROS metabolism. Wheat (Triticum aestivum L.) plants were grown under non-saline or saline conditions and were foliar sprayed with 75 mg L^-1 SA or 70 μM MT. The SA+MT combined treatment significantly increased N, P, K⁺, Fe, Zn, and Cu acquisition, accompanied by significantly lower Na⁺ accumulation in salt-stressed plants compared to non-stressed ones. Additionally, it significantly enhanced ATP content and H⁺-pump activity of the roots. The mitigation was also detected in the reduced superoxide radical content, electrolyte leakage, and lipoxygenase activity, as well as increased superoxide dismutase, catalase, peroxidase, and polyphenol oxidase activities; K⁺/Na⁺, Ca²⁺/Na⁺, and Mg²⁺/Na⁺ ratios; relative water content; membrane stability index; and free amino acid accumulation in treated plants. The novel evidence shows that the higher root H⁺-pump activity in treated plants is a tolerance mechanism that increases the salt tolerance via maintaining ionic homeostasis.

Keywords: antioxidant response; melatonin; nutrient uptake; root H+-pump activity; salicylic acid; salt stress; wheat (Triticum aestivum L.).

Figure 1

Influence of salicylic acid (SA, 75 mg L⁻¹), melatonin (MT, 70 μM), and SA (75 mg L⁻¹) + MT (70 μM) foliar application treatments on the concentrations of (a) nitrogen (N), (b) phosphorus (P), (c) potassium (K⁺), (d) sodium (Na⁺), (e) calcium (Ca²⁺), (f) magnesium (Mg²⁺), (g) iron (Fe), (h) zinc (Zn), and (i) copper (Cu) (mg g⁻¹ DW) in shoots of wheat plants grown under 0.1, 6, and 12dS m⁻¹ salinity levels. Data are means of four replicates (n = 4) and bars show standard errors (±SE). Asterisk represent significant differences between treatments at the p < 0.05 level according to LSD test.

Figure 2

Influence of salicylic acid (SA, 75 mg L⁻¹), melatonin (MT, 70 μM), and SA (75 mg L⁻¹) + MT (70 μM) foliar application treatments on the concentrations of (a) nitrogen (N), (b) phosphorus (P), (c) potassium (K⁺), (d) sodium (Na⁺), (e) calcium (Ca²⁺), (f) magnesium (Mg²⁺), (g) iron (Fe), (h) zinc (Zn), and (i) copper (Cu) (mg g⁻¹ DW) in grains of wheat plants grown under 0.1, 6, and 12dS m⁻¹ salinity levels. Data are means of four replicates (n = 4) and bars show standard errors (±SE). Asterisk represent significant differences between treatments at the p < 0.05 level according to LSD test.

Figure 3

Influence of salicylic acid (SA, 75 mg L⁻¹), melatonin (MT, 70 μM), and SA (75 mg L⁻¹) + MT (70 μM) foliar application treatments on the ratios of (a) K⁺/Na⁺, (b) Ca²⁺/Na⁺, and (c) Mg²⁺/Na⁺ in shoots, as well as (d) K⁺/Na⁺, (e) Ca²⁺/Na⁺, and (f) Mg²⁺/Na⁺ in grains of wheat plants grown under 0.1, 6, and 12 dS m⁻¹ salinity levels. Data are means of four replicates (n = 4) and bars show standard errors (±SE). Asterisk represent significant differences between treatments at the p < 0.05 level according to LSD test.

Figure 4

Influence of salicylic acid (SA, 75 mg L⁻¹), melatonin (MT, 70 μM), and SA (75 mg L⁻¹) + MT (70 μM) foliar application treatments on the (a) ATP content, (b) plasma membrane (PM) H⁺ -ATPase activity, (c) vacuole membrane (VM) H⁺ -ATPase activity, and (d) vacuole membrane (VM) H⁺-PPase activity in roots of wheat plants grown under 0.1, 6, and 12dS m⁻¹ salinity levels. Data are means of four replicates (n = 4) and bars show standard errors (±SE). Asterisk represent significant differences between treatments at the p < 0.05 level according to LSD test.

Figure 5

Influence of salicylic acid (SA, 75 mg L⁻¹), melatonin (MT, 70 μM), and SA (75 mg L⁻¹) + MT (70 μM) foliar application treatments on the (a) electrolyte leakage (%), (b) membrane stability index(%), and (c) lipoxygenase (LOX) activity levels in leaves of wheat plants grown under 0.1, 6, and 12 dS m⁻¹ salinity levels. Data are means of four replicates (n = 4) and bars show standard errors (±SE). Asterisk represent significant differences between treatments at the p < 0.05 level according to LSD test.

Figure 6

Influence of salicylic acid (SA, 75 mg L⁻¹), melatonin (MT, 70 μM), and SA (75 mg L⁻¹) + MT (70 μM) foliar application treatments on the activitylevels of (a) superoxide dismutase (SOD), (b) catalase (CAT), (c) peroxidase (POD), and (d) polyphenol oxidase (PPO) in leaves of wheat plants grown under 0.1, 6, and 12 dS m⁻¹ salinity levels. Data are means of four replicates (n = 4) and bars show standard errors (±SE). Asterisk represent significant differences between treatments at the p < 0.05 level according to LSD test.

Figure 7

Foliar applications of SA and MT alleviate salt stress impacts on wheat growth and productivity by improving the ATP content, root H⁺-pump activity, water content, and ROS detoxification, which in turn maintain the ionic homeostasis.