Deciphering Reserve Mobilization, Antioxidant Potential, and Expression Analysis of Starch Synthesis in Sorghum Seedlings under Salt Stress

Abstract

Salt stress is one of the major constraints affecting plant growth and agricultural productivity worldwide. Sorghum is a valuable food source and a potential model for studying and better understanding the salt stress mechanics in the cereals and obtaining a more comprehensive knowledge of their cellular responses. Herein, we examined the effects of salinity on reserve mobilization, antioxidant potential, and expression analysis of starch synthesis genes. Our findings show that germination percentage is adversely affected by all salinity levels, more remarkably at 120 mM (36% reduction) and 140 mM NaCl (46% reduction) than in the control. Lipid peroxidation increased in salt-susceptible genotypes (PC-5: 2.88 and CSV 44F: 2.93 nmloe/g.FW), but not in tolerant genotypes. SSG 59-3 increased activities of α-amylase, and protease enzymes corroborated decreased starch and protein content, respectively. SSG 59-3 alleviated adverse effects of salinity by suppressing oxidative stress (H₂O₂) and stimulating enzymatic and non-enzymatic antioxidant activities (SOD, APX, CAT, POD, GR, and GPX), as well as protecting cell membrane integrity (MDA, electrolyte leakage). A significant increase (p ≤ 0.05) was also observed in SSG 59-3 with proline, ascorbic acid, and total carbohydrates. Among inorganic cations and anions, Na⁺, Cl^-, and SO₄^2- increased, whereas K⁺, Mg²⁺, and Ca²⁺ decreased significantly. SSG 59-3 had a less pronounced effect of excess Na⁺ ions on the gene expression of starch synthesis. Salinity also influenced Na+ ion efflux and maintained a lower cytosolic Na⁺/K⁺ ratio via concomitant upregulation of SbNHX-1 and SbVPPase-I ion transporter genes. Thus, we have highlighted that salinity physiologically and biochemically affect sorghum seedling growth. Based on these findings, we highlighted that SSG 59-3 performed better by retaining higher plant water status, antioxidant potential, and upregulation of ion transporter genes and starch synthesis, thereby alleviating stress, which may be augmented as genetic resources to establish sorghum cultivars with improved quality in saline soils.

Keywords: germination; ion transporters; proline; reserve food; salinity; sorghum; starch; α-amylase.

Figure 1

Germination experiment in sorghum genotypes under salt stress. (a): Petri plate experiment; (b): between-paper experiment.

Figure 2

Effect of salt stress on (a) relative water content, (b) photochemical quantum yield (F_v/F_m), and (c) chlorophyll stability index of sorghum genotypes. ^a–f Values with different superscripts in the same row are significantly different at p < 0.05.

Figure 3

Effect of salinity on (a) MDA, (b) ascorbic acid, (c) proline, and (d) total soluble carbohydrates of sorghum seedlings under saline stress. Values represent means ± S.E. ^a–f Values with different superscripts in the same row are significantly different at p < 0.05.

Figure 3

Effect of salinity on (a) MDA, (b) ascorbic acid, (c) proline, and (d) total soluble carbohydrates of sorghum seedlings under saline stress. Values represent means ± S.E. ^a–f Values with different superscripts in the same row are significantly different at p < 0.05.

Figure 4

Accumulation of inorganic cations and anions of sorghum seedlings due to oxidative stress. (a) Na⁺ content; (b) K⁺ content; (c) Mg²⁺ content; (d) Ca²⁺ content; (e) Cl⁻ content; (f) SO₄²⁻ content. Values represent means ± S.E. ^a–f Values with different superscripts in the same row are significantly different at p < 0.05.

Figure 4

Accumulation of inorganic cations and anions of sorghum seedlings due to oxidative stress. (a) Na⁺ content; (b) K⁺ content; (c) Mg²⁺ content; (d) Ca²⁺ content; (e) Cl⁻ content; (f) SO₄²⁻ content. Values represent means ± S.E. ^a–f Values with different superscripts in the same row are significantly different at p < 0.05.

Figure 5

Effect of salinity on (a) starch and (b) protein content in germinating seeds of sorghum. Each value is the mean of triplicate. ^a–f Values with different superscripts in the same row are significantly different at p < 0.05.

Figure 6

Effect of salinity on (a) α-amylase and (b) protease activity in germinating sorghum seedlings. Each value is the mean of triplicate. ^a–f Values with different superscripts in the same row are significantly different at p < 0.05.

Figure 7

Effect of salt stress on (a) superoxide dismutase (SOD), (b) catalase (CAT), (c) peroxidase (POD), (d) ascorbate peroxidase (APX), (e) glutathione peroxidase (GPX), and (f) glutathione reductase (GR) of sorghum genotypes. Values are means of at least three replicates and significant differences between means, as determined by Tukey’s test (p < 0.05).

Figure 7

Effect of salt stress on (a) superoxide dismutase (SOD), (b) catalase (CAT), (c) peroxidase (POD), (d) ascorbate peroxidase (APX), (e) glutathione peroxidase (GPX), and (f) glutathione reductase (GR) of sorghum genotypes. Values are means of at least three replicates and significant differences between means, as determined by Tukey’s test (p < 0.05).

Figure 8

Relative quantification of: (a) Sucrose synthase (SS), (b) granule-bound starch synthase (GBSS), (c) cysteine protease (XCP1), (d) α-amylase synthesis (α-amy), (e) sodium proton antiporter (NHX-1), (f) vacuolar-proton pyrophosphatase (VPPase-I), (g) actin (Act), and (h) PP2A.

Figure 9

Plots of principal components of four sorghum lines. (a) scree plot; (b) loading plot; (c) biplot; (d) score plot.