24-Epibrassinolide (EBR) Confers Tolerance against NaCl Stress in Soybean Plants by Up-Regulating Antioxidant System, Ascorbate-Glutathione Cycle, and Glyoxalase System

Abstract

: The present research was performed to assess the effect of 24-epibrassinolide (EBR) on salt-stressed soybean plants. Salt stress suppressed growth, biomass yield, gas exchange parameters, pigment content, and chlorophyll fluorescence, but all these parameters were up-regulated by EBR supply. Moreover, salt stress increased hydrogen peroxide, malondialdehyde, and electrolyte leakage. EBR supplementation reduced the accumulation of oxidative stress biomarkers. The activities of superoxide dismutase and catalase, and the accumulation of proline, glycinebetaine, total phenols, and total flavonoids increased with NaCl stress, but these attributes further increased with EBR supplementation. The activities of enzymes and the levels of non-enzymatic antioxidants involved in the Asc-Glu cycle also increased with NaCl stress, and further enhancement in these attributes was recorded by EBR supplementation. Salinity elevated the methylglyoxal content, but it was decreased by the EBR supplementation accompanying with up-regulation of the glyoxalase cycle (GlyI and GlyII). Salinity enhanced the Na⁺ uptake in root and shoot coupled with a decrease in uptake of Ca²⁺, K⁺, and P. However, EBR supplementation declined Na⁺ accumulation and promoted the uptake of the aforementioned nutrients. Overall, EBR supplementation regulated the salt tolerance mechanism in soybean plants by modulating osmolytes, activities of key enzymes, and the levels of non-enzymatic antioxidants.

Keywords: 24-epibrassinolide; Asc-Glu cycle; NaCl stress; antioxidants; glyoxalase cycle; growth; mineral uptake; soybean.

Figure 1

Ameliorating role of 24-epibrassinolide (EBR) on (A) length, (B) fresh weight, and (C) dry weight of shoot and root under NaCl toxicity in soybean. Data presented are the means ± SE (n = 5) and significant difference calculated between the means at p ≤ 0.05 using the Duncan’s multiple range test.

Figure 2

Effect of 24-epibrassinolide (EBR) on (A) pigment content and (B) chlorophyll fluorescence parameters under NaCl toxicity in soybean. Data presented are the means ± SE (n = 5) and significant difference between the means calculated at p ≤ 0.05 using the Duncan’s multiple range test.

Figure 3

Effect of exogenously applied 24-epibrassinolide (EBR) on (A) CO₂ assimilation rate (A), (B) transpiration rate (E), and (C) stomatal conductance (g_s) in soybean under NaCl toxicity. Data presented are the means ± SE (n = 5) and significant difference between the means calculated at p ≤ 0.05 using Duncan’s multiple range test.

Figure 4

Exogenously applied 24-epibrassinolide (EBR) enhanced the proline (A) and glycine betaine (GB) (B) content in soybean under NaCl stress. Data presented are the means ± SE (n = 5) and significant difference between the means calculated at p ≤ 0.05 using the Duncan’s multiple range test.

Figure 5

Exogenously applied 24-epibrassinolide (EBR) reduced the H₂O₂ (A) and malondialdehyde (MDA) (B) contents as well as electrolyte leakage (EL) (C) in soybean plants under NaCl stress. Data presented are the means ± SE (n = 5) and significant difference between the means calculated at p ≤ 0.05 using the Duncan’s multiple range test.

Figure 6

Exogenously applied 24-epibrassinolide (EBR) enhanced the activities of (A) superoxide dismutase (SOD), (B) catalase (CAT), (C) ascorbate peroxidase (APX), (D) glutathione reductase (GR), (E) Dehydroascorbate reductase (DHAR), (F) manodehydroascorbate reductase (MDHAR), (G) ascorbate (AsA) content, (H) glutathione (GSH) content, and (I) GSSG content in soybean plants under NaCl stress. Data presented are the means ± SE (n = 5) and significant difference between the means calculated at p ≤ 0.05 using the Duncan’s multiple range test.

Figure 7

24-epibrassinolide (EBR) declines methylglyoxal (MG) content (A) and enhances GlyI and GlyII (B) under NaCl toxicity in soybean. Data presented are the means ± SE (n = 5) and significant difference between the means calculated at p ≤ 0.05 using the Duncan’s multiple range test.

Figure 8

Effect of 24-epibrassinolide (EBR) on (A) total phenol content and (B) total flavonoid content in soybean plants under NaCl stress. Data presented are the means ± SE (n = 5) and significant difference between the means calculated at p ≤ 0.05 using the Duncan’s multiple range test.

Figure 9

Effect of 24-epibrassinolide (EBR) on shoot and root mineral contents (A) Na content, (B) K content, (C) K/Na ratio, (D) Ca content, and (E) P content in soybean plants under NaCl stress. Data presented are the means ± SE (n = 5) and significant difference between the means calculated at p ≤ 0.05 using the Duncan’s multiple range test.