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Article

Exogenous Substances Improved Salt Tolerance in Cotton

by
Zhiduo Dong
1,2,†,
Ajing Meng
1,2,†,
Tong Qi
1,2,*,
Jian Huang
1,2,*,
Huicong Yang
1,2,
Aziguli Tayir
1,2 and
Bo Wang
1,2
1
Institute of Soil Fertilizer and Agricultural Water Saving, Xinjiang Academy of Agricultural Sciences, Urumqi 830091, China
2
Key Laboratory of Saline-Alkali Soil Improvement and Utilization (Saline-Alkali Land in Arid and Semi-Arid Regions), Ministry of Agriculture and Rural Affairs, Urumqi 830091, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Agronomy 2024, 14(9), 2098; https://doi.org/10.3390/agronomy14092098
Submission received: 2 August 2024 / Revised: 12 September 2024 / Accepted: 13 September 2024 / Published: 14 September 2024
(This article belongs to the Special Issue Bioactive Compounds for Plant Health and Protection)
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Versions Notes

Abstract

:
Soil salinization is a major limiting factor for cotton growth in Southern Xinjiang. Studying technologies and mechanisms to improve cotton salt tolerance is of significant importance for the development and utilization of saline–alkaline land. In this study, ‘Xinluzhong 40’ cotton was used as the material, and 150 mmol·L−1 sodium chloride (NaCl) and 1.2% natural saline–alkaline soil extract were employed to simulate single-salt (SS) and mixed-salt (MS) stresses, respectively. The effects of different exogenous substances (sodium nitrophenolate, 24-epibrassinolide, and γ-aminobutyric acid) on the growth characteristics of cotton under salt stress were investigated. The results show that: (1) Under salt stress, the height and biomass of cotton (50 d old) were reduced. Both SS and MS stresses led to increased superoxide dismutase (SOD) activity, elevated proline (PRO) content (with an increase of 50.01% and no significant difference), and increased malondialdehyde (MDA) content (with increases of 63.14% and 32.42%, respectively). At the same time, catalase (CAT) activity decreased, Na+ and Cl− contents increased, K+ content decreased, and the K+/Na+ ratio was reduced. (2) Application of sodium nitrophenolate (S), 24-epibrassinolide (E), and γ-aminobutyric acid (G) significantly improved SOD activity and PRO content while reducing MDA content (decreased by 29.33%, 25.48%, and 30.47% compared to SS treatment; and 1.68%, 5.21%, and 5.49% compared to MS treatment, respectively). They also increased CAT activity (increased by 75.97%, 103.24%, and 80.79% compared to SS treatment; and 91.06%, 82.43%, and 119.68% compared to MS treatment, respectively) and K+/Na+ ratio (increased by 57.59%, 66.35%, and 70.50% compared to SS treatment; and 38.31%, 42.97%, and 66.66% compared to MS treatment, respectively), reduced Cl− content, and promoted increases in plant height and biomass. The effects of exogenous substances on antioxidant capacity and ion balance under salt stress were significant, particularly under SS stress. (3) Principal component analysis revealed that under SS and MS stresses, principal component 1 mainly reflects cotton’s antioxidant capacity, with SOD, CAT, and PRO having high weights; principal component 2 mainly reflects cotton’s ion balance and nutrient absorption, with root Na+, stem Na+, leaf Na+, root K+, and root Cl− having high weights. These findings highlight the potential of exogenous substances to improve cotton salt tolerance and provide scientific evidence for cotton cultivation on saline–alkaline land, offering new insights into cultivation techniques from an applied research perspective.

1. Introduction

Xinjiang, located in the arid inland region of northwest China, is characterized by scarce precipitation and limited freshwater resources [1]. Approximately 10.1 million hectares of this region are classified as saline–alkaline land, with saline–alkaline soils covering around 7.27 million hectares. Severe land degradation has led to significant soil salinization, affecting about one-third of the arable land and severely restricting local agricultural productivity [2]. Despite these challenges, Xinjiang remains a crucial high-quality cotton production base in China [3,4]. Cotton farming is not only a key driver of the local economy but also a major contributor to the national cotton supply, underscoring its strategic importance for both national food security and cotton supply [5,6].
Cotton is considered a moderately salt-tolerant crop with a salt threshold of 7.7 dS·m−1, but it is often significantly affected by salt stress [7,8]. Salt stress impacts cotton through several mechanisms, including osmotic imbalance, ion toxicity, and oxidative damage [9]. Osmotic stress hinders the absorption of water and nutrients by cotton seeds and roots. Elevated levels of Na+ and Cl− ions interfere with cellular metabolism and compromise cell membrane integrity, ultimately leading to cellular dysfunction or death [8,10,11,12]. Moreover, prolonged exposure to high salt concentrations leads to excessive production of reactive oxygen species (ROS), which causes lipid peroxidation of cell membranes, damage to DNA and proteins, and can impair plant growth or even cause plant death [13,14,15]. Research indicates that increasing salt concentrations negatively affect cotton seed germination and seedling growth [8,13]. For example, in sand culture, cotton seed germination rates were 68–89% at a salt concentration of 150 mmol·L−1, but fell to 24–40% at 250 mmol·L−1; in soil, the germination rates were 72–89% at 15 dS·m−1, decreasing to 20–53% at 25 dS·m−1 [8]. Additionally, studies have shown that low salt concentrations (≤1.2%) have minimal impact on cotton germination, while higher concentrations (≥1.2%) significantly inhibit it [16]. These findings underscore the varying impact of salt concentrations on cotton growth. Despite its moderate salt tolerance, cotton is especially vulnerable to salt stress during germination and seedling stages, making it essential to improve its adaptability to saline–alkali soils during these critical growth periods [13,17].
Exogenous substances can enhance salt tolerance in plants by modulating their physiological responses to stressful conditions and are increasingly utilized in agricultural practices [18]. Several exogenous substances, including sodium nitrophenolate, 24-epibrassinolide, and γ-aminobutyric acid, have been extensively researched for their roles in alleviating plant stress. These substances improve plant resilience against environmental stressors, particularly under saline conditions, by influencing crucial physiological processes. Sodium nitrophenolate, a water-soluble phenolic compound, helps plants withstand stress by promoting the synthesis of proline and polyols, making it both effective and cost-efficient [19]. For instance, under salt stress (1000, 2000, and 3000 ppm), applying 2 mL·L−1 of sodium nitrophenolate markedly improved the growth of Calendula officinalis, enhancing its chlorophyll content, number of ray florets, inflorescence diameter, total flavonoid content, and catalase activity [20]. 24-epibrassinolide, a plant sterol classified by many physiologists as a growth-promoting hormone, is widely applied in agriculture [21,22]. Under 3 g·L−1 sodium chloride (NaCl) stress, soaking seeds in 0.1 mg·L−1 24-epibrassinolide significantly increased levels of indoleacetic acid, zeatin, and salicylic acid in rice seedlings, while decreasing abscisic acid content. This treatment mitigated growth inhibition due to salt stress, as evidenced by significant improvements in root length and plant height, and helped maintain normal photosynthetic metabolism [21]. γ-aminobutyric acid, a four-carbon non-protein amino acid, functions as both a defense substance and a signaling molecule, aiding plants in managing both biotic and abiotic stresses [23]. Under 100 mmol·L−1 NaCl stress, soaking seeds in 1 µmol·L−1 γ-aminobutyric acid activated H+-ATPase, maintained cellular K+, excluded Na+, and enhanced antioxidant enzyme activity, thereby reducing salt stress damage in clover seedlings [14].
While numerous studies have demonstrated the effectiveness of sodium nitrophenolate, 24-epibrassinolide, and γ-aminobutyric acid in enhancing plant salt tolerance, their specific effects on cotton remain underexplored. Most of the existing research utilizes NaCl as the stress agent to assess salt tolerance, given its prevalence as one of the most common salts in saline–alkaline soils [17,24]. Typically, studies investigating the enhancement of cotton salt tolerance with exogenous substances use 150 mmol·L−1 NaCl to simulate salt stress [13,25]. However, fewer studies have employed natural saline–alkaline soil extracts as stress agents to better mimic field conditions. In Southern Xinjiang, where cotton cultivation occupies two-thirds of the region’s cotton-growing area [26]. understanding the impacts of these exogenous substances is crucial. This study investigates the effects of sodium nitrophenolate, 24-epibrassinolide, and γ-aminobutyric acid on the germination, seedling growth, and physiological characteristics of Xinluzhong 40 (Gossypium hirsutum L.) cotton under two types of salt stress (single-salt and mixed-salt conditions). The findings aim to provide practical insights for cotton cultivation in saline–alkaline soils.

2. Materials and Methods

2.1. Experimental Location and Materials

The experiment was conducted from August to October 2023 in the climate chamber of the Baicheng Agricultural Experimental Station, Xinjiang Academy of Agricultural Sciences (81°87′ N, 41°80′ E). The artificial climate chamber conditions were set at 25 °C, 70% relative humidity, 12 h of light/12 h of darkness, with a light intensity of 284 μmol·m−2·s−1. The test material upland cotton variety ‘Xinluzhong 40’ was provided by Aksu Kerun Seed Industry Co., Ltd. (Alar, China), with a thousand-grain weight of 91.97 g and a germination rate of about 93.33%. Each seedling tray has 50 cells, with each cell having a top diameter of 48 mm, a bottom diameter of 18 mm, and a depth of 93 mm. sodium nitrophenolate was obtained from Jining Runtian Biological Technology Co., Ltd. (Jining, China). 24-epibrassinolide was acquired from Hebei Lansheng Biotechnology Co., Ltd. (Jinzhou, China). γ-aminobutyric acid was obtained from Shanghai McLean Biochemical Technology Co., Ltd. (Shanghai, China). Sodium chloride was obtained from Tianjin Xinbote Chemical Co., Ltd. (Tianjin, China). The natural saline–alkaline soil extract was prepared by diluting a 27.21% high-salt solution obtained through leaching salt–alkali soil from Yuepuhu County (76°77′ N, 39°19′ E), Kashgar, with a salt content of 272.1 g·kg−1. The pH value, mineralization, and concentrations of the eight major ions are presented in Table 1. The pH value was determined using a digital pH meter (pHS.25 type), and conductivity was measured using a conductivity meter (PE38). The ion determination methods used were as follows: HCO3− and CO32− were determined using double indicator titration, Cl− was determined through AgNO3− titration, SO42− was determined through EDTA indirect titration, Ca2+ and Mg2+ were determined through EDTA complexometric titration, and K+ and Na+ were determined using flame photometry.

2.2. Experimental Design

To better simulate the actual conditions of field production in Xinjiang, we employed a “dry sowing, wet emergence” drip irrigation cultivation model to reflect the common salt stress environments in the region. In this experimental design, we selected cotton seeds that were full and uniform in size. The seeds were first sown in cell trays with a vermiculite substrate [27], with one seed per cell. After sowing, 35 mL of treatment solution was added to each cell (the volume of 35 mL was determined through preliminary experiments to ensure that the mixture did not drip when squeezed). The treatment solution, a mixture of salts and exogenous substances, was covered with a layer of plastic wrap. The plastic wrap was removed on the third day after sowing, at which point the germination rate of the cotton seeds in the control group reached 85%.
To simulate the salt stress environment, we used a 150 mmol·L−1 NaCl solution and a 1.2% natural saline–alkali soil extract. The salt concentration of the 150 mmol·L−1 NaCl solution was approximately 8.77 g·L−1, which is a common and controllable laboratory method for simulating salt stress and significantly impacts cotton growth and development [13]. Additionally, we used a 1.2% natural saline–alkali soil extract, which contained various salts and minerals, including calcium ions (Ca2+), magnesium ions (Mg2+), potassium ions (K+), and other trace elements. The presence of these minerals could potentially promote cotton growth, as the interactions between trace elements and salts may mitigate salt-induced damage to the plants.
The concentrations of the treatment solutions were determined through preliminary experiments and included 12 mg·L−1 sodium nitrophenolate, 0.15 mg·L−1 24-epibrassinolide, and 309.3 mg·L−1 (2 mmol·L−1) γ-aminobutyric acid, with distilled water used as the control. Each set of 10 cotton seedlings constituted one replicate, and each treatment was replicated three times [28]. This design effectively simulated the actual conditions under salt stress and allowed for a detailed assessment of the effects of different treatments on cotton growth.

2.3. Index Determination and Methods

2.3.1. Growth Index Determination

At 50 d after sowing, three seedlings were randomly selected from each treatment group. The height from the ground to the cotyledon node was measured using a ruler to determine the plant height [28]. The seedlings were then separated into roots, stems, and leaves. Each part was blanched at 105 °C for 30 min, and then dried in an electric oven at 80 °C until a constant weight was reached [27]. Finally, each part was weighed to obtain the dry weight.

2.3.2. Physiological Index Measurement

To determine the proline content, we first took 0.5 g of leaves and mixed them with 5 mL of a 3% sulfosalicylic acid solution, ensuring that the process was carried out under cold conditions. The mixing was performed using a mortar and pestle, following the method described by Lu et al. [9]. Subsequently, we placed the mixture in a centrifuge and centrifuged it at 10,000× g for 12 min to obtain the supernatant. Next, we took 1 mL of the supernatant and mixed it thoroughly with 1 mL of acid ninhydrin and 1 mL of glacial acetic acid. The mixture was then incubated at 95 °C in a hot water bath for 10 min. After the incubation, the mixture solution was transferred to a clean test tube and placed in an ice-containing box for proper cooling. Following that, 2 mL of toluene were added to the cooled solution, and the solution was thoroughly vortexed. Finally, we recorded the absorbance of the toluene containing the chromophore spectrophotometrically at a wavelength of 520 nm, and the proline content was estimated using a standard curve generated from known concentrations.
To determine the content of malondialdehyde (MDA), following the method described by Keya et al. [29]. was followed. Initially, 0.5 g of leaves was taken and incubated with 5 mL of thiobarbituric acid (TBA) at 95 °C in a water bath. After 30 min of incubation, the mixture was transferred to a new transparent test tube and appropriately cooled in an ice-containing box. Subsequently, centrifugation was carried out at 10,000× g for 10 min at 25 °C. Next, 200 μL of the supernatant was pipetted into a micro quartz cuvette or a 96-well plate, and the absorbance at 532 nm and 600 nm was measured using a UV-visible spectrophotometer (Beijing Persee General Instrument Co., Ltd., Beijing, China). Finally, the content of MDA was estimated by calculating the difference in absorbance between 532 nm and 600 nm, allowing for the determination of the degree of lipid peroxidation in leaves.
To determine enzyme activity, we need to obtain clean leaf samples and immediately cool them with liquid nitrogen after sampling. After cooling, the samples are stored in a −80 °C freezer for later use. In the analysis of antioxidant enzymes, we used 0.5 g of cotton seedling leaves. First, fresh leaf tissues are ground in a cold water bath and mixed with pH 7.4, 0.05 mol·L−1 phosphate-buffered saline. Subsequently, the supernatant obtained by centrifugation at 8000× g for 10 min at 4 °C is used for the subsequent analysis of antioxidant enzyme activity. Superoxide dismutase (SOD) activity is determined using the nitroblue tetrazolium (NBT) photoreduction method [30]. Additionally, catalase (CAT) activity was measured using the ultraviolet absorption method [15]. To determine the activity of superoxide dismutase (SOD) and catalase (CAT), we utilized specific assay kits, namely SOD-1-W and CAT-1-Y, respectively. These assay kits were provided by Suzhou Keming Biotechnology Co., Ltd. (Suzhou, China).
After drying and weighing, the samples are ground and sieved. To measure chloride ion content, we use a chlorine (Cl−) kit from Suzhou Keming Biotechnology Co., Ltd. (Suzhou, China). Sodium (Na+) and potassium (K+) ion contents in the plants are determined using flame photometry [9].

2.4. Statistical Analysis

Experimental data management was carried out using Excel 2016. Single-factor analysis of variance (ANOVA) was performed using SPSS 26.0, followed by Duncan’s post hoc test to determine the significance of differences (p < 0.05 is considered significant). Bar charts were created using Origin 2018. Principal component analysis (PCA) was carried out using RStudio IDE (version 2023.06.0+421) and R (version 4.3.1). The first two principal components (PC1 and PC2) were extracted.

3. Results

3.1. Growth Characteristics

Under salt stress conditions, cotton growth parameters showed a general decline (Table 2). Compared to the control (CK), both single-salt (SS) and mixed-salt (MS) treatments inhibited the height and dry biomass of cotton seedlings. The SS treatment reduced the plant height by 14.66%, while the MS treatment decreased it by 12.86%, demonstrating a clear inhibitory effect of salt stress on plant growth. Regarding dry biomass, the SS treatment significantly reduced root dry weight by 56.54% and leaf dry weight by 30.24%, whereas the stem dry weight only decreased by 5.16%, indicating that SS stress had a more severe impact on roots and leaves. In contrast, the MS treatment caused smaller reductions in root dry weight (40.26%), stem dry weight (2.66%), and leaf dry weight (13.91%), with no significant differences, suggesting that the overall impact of mixed-salt stress was relatively mild.
Under the treatment with exogenous substances, cotton seedlings showed noticeable improvement in growth. Application of sodium nitrophenolate (S), 24-epibrassinolide (E), and γ-aminobutyric acid (G) significantly increased plant height under both SS and MS stress. Compared to the SS treatment, SS+S, SS+E, and SS+G treatments increased plant height by 14.59%, 11.83%, and 15.07%, respectively; compared to the MS treatment, MS+S, MS+E, and MS+G treatments increased plant height by 11.11%, 8.41%, and 14.29%, respectively. These results indicate that exogenous substances can effectively mitigate the inhibitory effects of salt stress on plant height.
Although changes in dry biomass did not reach statistical significance, compared to the SS treatment, the root dry weight was increased by 29.05%, 8.49%, and 54.77% for the SS+S, SS+E, and SS+G treatments, respectively. Compared to the MS treatment, root dry weight increased by 11.60%, 5.04%, and 33.11% for MS+S, MS+E, and MS+G treatments, respectively. The increases in stem dry weight and leaf dry weight were relatively small but still showed a positive trend. For example, the leaf dry weight increased by 10.62%, 15.73%, and 22.42% for SS+S, SS+E, and SS+G treatments compared to the SS treatment; for MS+S, MS+E, and MS+G treatments, leaf dry weight increased by 2.76%, 2.81%, and 5.92% compared to the MS treatment.
Overall, salt stress significantly inhibited cotton growth, while the application of exogenous substances (sodium nitrophenolate, 24-epibrassinolide, and γ-aminobutyric acid) notably improved plant height and to some extent promoted the accumulation of dry biomass in roots, stems, and leaves, with a particularly significant effect on height recovery.

3.2. Proline Content

Under salt stress conditions, the proline (PRO) content in cotton leaves showed significant changes. Single-salt (SS) treatment significantly increased PRO content, with an increase of 50.01% compared to the control (CK) (p < 0.05), indicating that single-salt stress had a notable impact on the osmotic regulation capacity of cotton seedling leaves. In contrast, the PRO content under mixed-salt (MS) treatment did not show a significant difference compared to the control (CK) (Figure 1).
Under SS and MS stress, the exogenous treatments with sodium nitrophenolate (S), 24-epibrassinolide (E), and γ-aminobutyric acid (G) further increased the PRO content in cotton leaves. The increase in PRO content among the treatment groups followed the order of G > E > S. Specifically, G treatment increased PRO content by 17.84% and 27.80% under SS and MS stress, respectively; E treatment increased it by 12.55% and 20.21%; and S treatment showed a relatively smaller increase of 7.01% and 5.08%, respectively. These results suggest that the application of exogenous substances, especially γ-aminobutyric acid (G), significantly enhanced the osmotic regulation capacity of cotton leaves, effectively alleviating the negative effects of salt stress.

3.3. Malondialdehyde Content

Under salt stress conditions, the malondialdehyde (MDA) content in cotton seedling leaves significantly increases, indicating a marked impact of salt stress on lipid peroxidation. Compared to the control (CK), the MDA content in leaves subjected to single-salt (SS) and mixed-salt (MS) treatments was notably higher. Specifically, the MDA content increased by 63.14% under SS treatment and by 32.42% under MS treatment (Figure 2).
Under single-salt stress, the application of sodium nitrophenolate (S), 24-epibrassinolide (E), and γ-aminobutyric acid (G) significantly reduced the MDA content. In detail, treatments SS+S, SS+E, and SS+G reduced MDA content by 29.33%, 25.48%, and 30.47%, respectively, compared to SS treatment. In contrast, under mixed-salt stress, the reduction in MDA content with S, E, and G treatments was relatively modest, with reductions of 1.68%, 5.21%, and 5.49% compared to MS treatment, respectively. These results indicate that exogenous treatments, particularly γ-aminobutyric acid (G), are effective in reducing lipid peroxidation damage in cotton leaves caused by salt stress, especially under single-salt stress conditions.

3.4. Antioxidant Enzyme Activity

Under salt stress conditions, the activity of superoxide dismutase (SOD) in cotton leaves is significantly higher compared to the control (CK), with SOD activity in the single-salt (SS) and mixed-salt (MS) treatments being 22.57% and 13.56% higher than that of the control, respectively (Figure 3A). Conversely, the activity of catalase (CAT) in both the SS and MS treatments is notably lower than in the CK, with reductions of 56.79% and 45.32%, respectively (Figure 3B).
Under SS and MS stress conditions, the application of sodium nitrophenolate (S), 24-epibrassinolide (E), and γ-aminobutyric acid (G) significantly enhances the SOD and CAT activities in cotton. Under SS stress, the SOD activity in the SS+S, SS+E, and SS+G treatments increased by 12.73%, 9.32%, and 3.20% compared to the SS treatment, with SS+S showing a significant difference. Under MS stress, the SOD activity in the MS+S, MS+E, and MS+G treatments increased by 11.23%, 0.97%, and 7.32%, respectively.
Regarding CAT activity, the application of exogenous substances resulted in significant improvements. Under SS stress, the CAT activity in the SS+E, SS+G, and SS+S treatments increased by 103.24%, 80.79%, and 75.97%, respectively, compared to the SS treatment. Under MS stress, the CAT activity in the MS+G, MS+S, and MS+E treatments increased by 119.68%, 91.06%, and 82.43%, respectively, compared to the MS treatment. These results indicate that the application of exogenous substances can effectively enhance the antioxidant capacity of cotton seedlings under salt stress.

3.5. Ionic Content and K+/Na+ Ratio

Under salt stress conditions, the Cl− (Figure 4A) and Na+ contents (Figure 4B) in cotton seedlings significantly increased, while the K+ content decreased (Figure 4C). Compared to the control (CK), single-salt (SS) treatment increased Cl− content by 35.49%, 49.78%, and 36.12% in the roots, stems, and leaves, respectively. Na+ content increased by 115.27%, 93.87%, and 130.91%, while K+ content decreased by 28.54%, 27.83%, and 21.99%. Under mixed-salt (MS) treatment, Cl− content increased by 20.63%, 38.06%, and 32.21% in the roots, stems, and leaves, respectively. Na+ content increased by 91.05%, 77.00%, and 124.32%, while K+ content decreased by 23.79%, 21.55%, and 17.49% (Figure 4).
Under salt stress, the application of sodium nitrophenolate (S), 24-epibrassinolide (E), and γ-aminobutyric acid (G) effectively reduced the Cl− and Na+ contents in various parts of the cotton and increased the K+ content. For Cl− content, SS+G treatment resulted in the greatest reduction in the roots, with a decrease of 19.18%; MS+S treatment showed the largest reduction in the roots, with a decrease of 12.43%. In the stems, SS+E treatment led to the maximum reduction in Cl− content, with a decrease of 27.06%; MS+E treatment showed the greatest reduction, with 20.92%. In the leaves, SS+E treatment reduced Cl− content by 22.12%, while MS+G treatment had the largest reduction, with 16.23%.
For Na+ content, G treatment resulted in the greatest reduction in the roots, with SS+G treatment reducing Na+ by 16.75% compared to SS treatment; MS+G treatment reduced Na+ by 10.96% compared to MS treatment. In the stems, E treatment had the largest reduction, with SS+E treatment reducing Na+ by 27.92% compared to SS treatment; MS+E treatment reduced Na+ by 21.82% compared to MS treatment. In the leaves, SS+E treatment decreased Na+ content by 32.73%, while MS+G treatment showed the largest reduction at 34.10%.
The application of external substances also significantly affected K+ content. In the roots, S treatment resulted in the greatest increase under both salt stresses, with SS+S treatment increasing K+ by 33.31% compared to SS treatment; MS+S treatment increased K+ by 24.74% compared to MS treatment. In the stems, SS+E treatment showed the highest increase, with an increase of 19.39%; MS+G treatment showed the largest increase at 12.06%. In the leaves, G treatment led to the greatest increase under both salt stresses, with SS+G treatment increasing K+ by 15.32% compared to SS treatment; MS+G treatment increased K+ by 9.69% compared to MS treatment.
In summary, the application of sodium nitrophenolate, 24-epibrassinolide, and γ-aminobutyric acid significantly regulates the ion balance in cotton seedlings under salt stress, reducing Cl− and Na+ contents and increasing K+ content, thereby enhancing salt tolerance.

3.6. Principal Component Analysis

To further explore the relationships between treatments and various indicators, principal component analysis was performed under single-salt (Figure 5A) and mixed-salt (Figure 5B) stress. The analysis summarized the 17 indicators into two principal components, which explained 91.75% and 91.94% of the total variation, respectively. Under single-salt (SS) stress, indicators such as plant height (X1), root dry weight (X2), stem dry weight (X3), leaf dry weight (X4), malondialdehyde (MDA, X5), superoxide dismutase (SOD, X6), catalase (CAT, X7), proline (PRO, X8), root Na+ (X9), stem Na+ (X10), leaf Na+ (X11), root K+ (X12), stem K+ (X13), leaf K+ (X14), root Cl− (X15), stem Cl− (X16), and leaf Cl− (X17) all showed significant changes. Specifically, SS treatment caused the cotton to exhibit different distributions of indicators across quadrants. Treatments SS+ sodium nitrophenolate (S), SS+ 24-epibrassinolide (E), and SS+ γ-aminobutyric acid (G) significantly improved the salt tolerance of cotton, mainly reflected in the increased plant height, dry weight, and antioxidant indicators such as SOD and CAT. Under mixed-salt (MS) stress, X8, X6, X5, X9, and X10 concentrated in the first quadrant, indicating significant impacts of these indicators under MS stress. Compared to the control (CK) treatment, MS treatment caused changes in the indicators across all quadrants. Treatments MS+S and MS+E significantly improved the growth of cotton under MS stress, mainly reflected in the reduction in MDA content and the increase in antioxidant enzyme activity. Treatment MS+G also showed some improvement, particularly in increased plant height and dry weight. Overall, the analysis revealed that sodium nitrophenolate, 24-epibrassinolide, and γ-aminobutyric acid treatments effectively mitigated the adverse effects of salt stress on cotton to varying degrees. The key factors were the increase in antioxidant enzyme activities like SOD and CAT and the reduction in MDA content. Additionally, these substance treatments effectively regulated the ionic balance in cotton, reducing Na+ and Cl− content and increasing K+ content, thereby enhancing salt tolerance. Overall, substance treatments, especially sodium nitrophenolate and 24-epibrassinolide, demonstrated significant effects in improving the growth and physiological status of cotton seedlings under salt stress.

4. Discussion

This study explores the impact of various exogenous substances—sodium nitrophenolate, 24-epibrassinolide, and γ-aminobutyric acid—on cotton growth and its underlying salt tolerance mechanisms under salt stress conditions. We evaluated the potential of these substances to mitigate salt stress and enhance cotton growth by simulating two distinct salt stress environments: a 150 mmol·L−1 NaCl solution and a 1.2% natural saline–alkaline soil extract.
Salt stress resulted in a reduction in both cotton biomass and plant height, which aligns with previous findings [9,28]. Our experimental results show that both the 150 mmol·L−1 NaCl solution and 1.2% natural saline–alkali soil extract caused a decrease in cotton biomass and height, with a more noticeable reduction observed in plant height. This adverse effect is mainly due to the high salt concentration disrupting normal cellular physiological functions, thereby inhibiting plant growth [13]. Under these simulated salt stress conditions, all three exogenous substances—sodium nitrophenolate, 24-epibrassinolide, and γ-aminobutyric acid—effectively enhanced cotton growth performance, as indicated by increases in biomass and plant height. This suggests that these exogenous substances can effectively mitigate the adverse effects of salt stress on cotton. Specifically, sodium nitrophenolate treatment improved cotton growth under salt stress, consistent with the findings of Li et al. [31]. Sodium nitrophenolate likely alleviates salt stress by promoting mineral absorption and reducing oxidative damage [32]. Similarly, treatment with 24-epibrassinolide increased cotton biomass and height, in agreement with the results of Sousa et al. [15]. 24-epibrassinolide may enhance salt tolerance by modulating ion transport within the plant. Additionally, γ-aminobutyric acid treatment boosted cotton dry weight and plant height, which is in line with the findings of Cheng et al. [14]. γ-aminobutyric acid likely enhances salt tolerance by increasing antioxidant enzyme activity and regulating Na+/K+ transport genes under salt stress.
Proline (PRO), a common organic osmotic regulator, plays a critical role in enhancing plant salt tolerance [13,17]. Previous studies have shown that under 150 mmol·L−1 NaCl stress, the PRO content in cotton significantly increases, indicating that cotton can initiate self-protection mechanisms by synthesizing osmotic adjustment substances [13,33]. Our study’s results align with these findings. Treatments with sodium nitrophenolate, 24-epibrassinolide, and γ-aminobutyric acid further elevated the PRO content in cotton, contributing to enhanced osmotic pressure and reduced salt stress damage to cotton seedlings. Similar studies have demonstrated that sodium nitrophenolate treatment increases PRO content in cucumber seedlings under stress, thereby boosting their stress resistance [32]. Additionally, 24-epibrassinolide treatment has been reported to increase PRO and other osmotic adjustment substances in barley under salt stress [34]. Furthermore, γ-aminobutyric acid treatment has been shown to elevate PRO content in ryegrass under salt stress [30].
Salt stress leads to the excessive accumulation of reactive oxygen species (ROS) in plants, causing membrane lipid peroxidation and damaging cell membrane structure [30]. Malondialdehyde (MDA), a byproduct of membrane lipid peroxidation, is commonly used as an indicator of the extent of damage to plant cell membranes [12,25]. In response to ROS, the activities of key protective enzymes, such as superoxide dismutase (SOD) and catalase (CAT), often change to mitigate oxidative stress [10,35,36,37,38]. In this study, both types of salt stress increased MDA levels in the leaves of cotton seedlings, which is consistent with previous research [13,33,37]. Under salt stress conditions, SOD activity increased while CAT activity decreased in cotton seedlings’ leaves, aligning with previous findings [33]. Exogenous substances were found to improve the activity of antioxidant enzymes like SOD and CAT, enhancing the plants’ ability to scavenge ROS, thereby reducing membrane lipid peroxidation and mitigating MDA accumulation [17]. In this study, all three exogenous substances—sodium nitrophenolate, 24-epibrassinolide, and γ-aminobutyric acid—enhanced the activity of both antioxidant enzymes, with CAT activity showing more sensitivity to hormonal changes. This may be attributed to its regulation being primarily controlled by genetic and environmental interactions [39]. Previous studies have shown that sodium nitrophenolate can increase SOD and CAT activities under stress conditions, thereby enhancing the ability to clear intracellular ROS and reducing MDA levels [31,32]. Similarly, 24-epibrassinolide pretreatment has been reported to increase SOD and CAT activities in tomatoes under salt stress, reducing ROS-induced cell damage [15]. Furthermore, γ-aminobutyric acid treatment has been shown to improve the activities of various antioxidant enzymes and related gene transcription levels, effectively reducing ROS production [14].
When excessive Na+ and Cl− ions enter plant cells, they disrupt the ionic balance in the cytoplasm, leading to damage in cell membrane structure and function. This impairment affects the plant’s ability to absorb and transport essential nutrients such as Ca2+ and K+ [17]. Under 150 mmol·L−1 NaCl stress, an increase in Na+ and Cl− content in cotton cells was observed, accompanied by a decrease in K+ content, and the K+/Na+ ratio decreased. These results are consistent with previous studies [10,33,40]. An increased K+/Na+ ratio in cotton is generally indicative of stronger salt tolerance [9,10]. In this study, all three exogenous substances—sodium nitrophenolate, 24-epibrassinolide, and γ-aminobutyric acid—increased the K+/Na+ ratio and reduced Cl− content in cotton, suggesting that these substances slow down the influx of harmful ions, thereby protecting cell structure. Similar studies have shown that sodium nitrophenolate can promote the uptake of nitrogen, phosphorus, potassium, calcium, and magnesium in cucumber under low-temperature stress conditions, contributing to stress resistance [32]. 24-epibrassinolide treatment has been reported to help maintain ionic balance and enhance nutrient absorption, thereby alleviating the adverse effects of salt stress [15,41]. γ-Aminobutyric acid treatment was also found to increase the transcription levels of genes related to Na+/K+ transporters under salt stress, helping maintain ionic balance and reduce ion toxicity [14,30].
Previous research indicates that the optimal concentration of exogenous substances varies depending on the type of stress, mainly due to differences in plant sensitivity to various stressors [36,42]. The effects of exogenous substances can vary under different stress conditions, reflecting the plant’s specific physiological responses [13,23]. Additionally, different exogenous substances enhance plant stress tolerance through distinct mechanisms, leading to differential effects on plant performance [25,31]. Studies have shown that the alleviating effects of exogenous substances tend to be more pronounced under more severe environmental conditions [9,14,32,36]. In this study, principal component analysis (PCA) was used to reduce the dimensionality of 17 indicators, resulting in two principal components that explained 91.75% of the total variance under NaCl stress and 91.94% under natural saline–alkaline soil extract stress. This demonstrates the substantial and consistent impact of exogenous substances on enhancing cotton’s salt tolerance. The results reveal that sodium nitrophenolate (S), 24-epibrassinolide (E), and γ-aminobutyric acid (G) effectively enhance cotton’s salt tolerance under various salt stress conditions. Specifically, treatments with SS+S, SS+E, and SS+G significantly improved plant height, dry weight, and antioxidant enzyme activities (such as SOD and CAT). In comparison, MS+S and MS+E treatments were particularly effective in reducing MDA content and increasing antioxidant enzyme activities, while MS+G treatment showed notable improvements in plant height and dry weight. Overall, sodium nitrophenolate and 24-epibrassinolide were especially effective in enhancing cotton’s salt tolerance. These treatments significantly improved growth performance and physiological status under salt stress by enhancing antioxidant enzyme activities, reducing MDA content, and regulating ion balance. This study provides strong theoretical support for the application of exogenous substances to mitigate salt stress in cotton.

5. Conclusions

This study demonstrates that salt stress significantly inhibits the growth of cotton seedlings, characterized by reduced plant height and dry biomass, increased SOD activity and proline content, decreased catalase activity, elevated Na+ and Cl− levels, and reduced K+ content. Exogenous substances (sodium nitrophenolate, 24-epibrassinolide, and γ-aminobutyric acid) can significantly mitigate these negative effects, improving antioxidant capacity and ion balance and enhancing the salt tolerance of cotton. Principal component analysis shows that these exogenous substances have a notable effect on regulating cotton’s salt tolerance, especially under NaCl stress. These findings provide valuable scientific evidence for the cultivation of cotton in saline–alkaline soils.

Author Contributions

T.Q. and J.H. designed the experiment, Z.D., A.M., H.Y., A.T. and B.W. conducted the experiment, Z.D. and A.M. wrote the manuscript. A.M., T.Q. and J.H. provided laboratory and other technical support. T.Q. and J.H. critically reviewed and edited the manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

This study received funding from Major special projects of Xinjiang Autonomous Region (2022A02007-1) and the Xinjiang Province ‘Three Agriculture’ Key Talents Training Program (2022SNGGGCC026).

Data Availability Statement

The original contributions presented in the study are included in the article material, further inquiries can be directed to the corresponding authors.

Acknowledgments

We appreciate and thank the anonymous reviewers for helpful comments that led to an overall improvement of the manuscript. We also thank the Journal Editor Board for their help and patience throughout the review process.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Bai, Z.T.; Bai, W.Q.; Xie, C.; Yu, J.; Dai, Y.L.; Pei, S.Z.; Zhang, F.c.; Li, Y.X.; Fan, J.L.; Yin, F. Irrigation depth and nitrogen rate effects on seed cotton yield, fiber quality and water-nitrogen utilization efficiency in southern Xinjiang, China. Agric. Water Manag. 2023, 290, 108583. [Google Scholar] [CrossRef]
  2. Wang, R.S.; Kang, Y.H.; Wan, S.Q. Effects of different drip irrigation regimes on saline–sodic soil nutrients and cotton yield in an arid region of Northwest China. Agric. Water Manag. 2015, 153, 1–8. [Google Scholar] [CrossRef]
  3. Lin, S.D.; Wang, Q.J.; Deng, M.J.; Su, L.J.; Wei, K.; Guo, Y.; Zhang, J.H. Assessing the influence of water fertilizer, and climate factors on seed cotton yield under mulched drip irrigation in Xinjiang Agricultural Regions. Eur. J. Agron. 2024, 152, 127034. [Google Scholar] [CrossRef]
  4. Hou, X.H.; Fan, J.L.; Zhang, F.C.; Hu, W.H.; Xiang, Y.Z. Optimization of water and nitrogen management to improve seed cotton yield, water productivity and economic benefit of mulched drip-irrigated cotton in southern Xinjiang, China. Field Crops Res. 2024, 308, 109301. [Google Scholar] [CrossRef]
  5. Zhu, Y.Q.; Sun, L.; Luo, Q.Y.; Chen, H.Y.; Yang, Y.D. Spatial optimization of cotton cultivation in Xinjiang: A climate change perspective. Int. J. Appl. Earth Obs. Geoinf. 2023, 124, 103523. [Google Scholar] [CrossRef]
  6. Xiao, C.; Ji, Q.Y.; Zhang, F.C.; Li, Y.; Fan, J.L.; Hou, X.H.; Yan, F.L.; Liu, X.Q.; Gong, K.Y. Effects of various soil water potential thresholds for drip irrigation on soil salinity, seed cotton yield and water productivity of cotton in northwest China. Agric. Water Manag. 2023, 279, 108172. [Google Scholar] [CrossRef]
  7. Ashraf, M. Salt tolerance of cotton: Some new advances. Crit. Rev. Plant Sci 2002, 21, 1–30. [Google Scholar] [CrossRef]
  8. Maryum, Z.; Luqman, T.; Nadeem, S.; Khan, S.M.U.D.; Wang, B.; Ditta, A.; Khan, M.K.R. An overview of salinity stress, mechanism of salinity tolerance and strategies for its management in cotton. Front. Plant Sci. 2022, 13, 907937. [Google Scholar] [CrossRef]
  9. Lu, K.S.; Yan, L.; Riaz, M.; Babar, S.; Hou, J.Y.; Zhang, Y.L.; Jiang, C. Exogenous boron alleviates salt stress in cotton by maintaining cell wall structure and ion homeostasis. Plant Physiol. Biochem. 2023, 201, 107858. [Google Scholar] [CrossRef]
  10. Chen, L.; Li, L.T.; Lu, B.; Ma, T.T.; Jiang, D.; Li, J.; Zhang, K.; Sun, H.C.; Zhang, Y.J.; Bai, Z.Y.; et al. Exogenous melatonin promotes seed germination and osmotic regulation under salt stress in cotton (Gossypium hirsutum L.). PLoS ONE 2020, 15, e0228241. [Google Scholar] [CrossRef]
  11. Ren, F.T.; Yang, G.; Li, W.J.; He, X.L.; Gao, Y.L.; Tian, L.J.; Li, F.D.; Wang, Z.L.; Liu, S.H. Yield-compatible salinity level for growing cotton (Gossypium hirsutum L.) under mulched drip irrigation using saline water. Agric. Water Manag. 2021, 250, 106859. [Google Scholar] [CrossRef]
  12. Sheri, V.; Kumar, M.; Jaconis, S.; Zhang, B.H. Antioxidant defense in cotton under environmental stresses: Unraveling the crucial role of a universal defense regulator for enhanced cotton sustainability. Plant Physiol. Biochem. 2023, 204, 108141. [Google Scholar] [CrossRef] [PubMed]
  13. Li, H.P.; Sun, H.C.; Ping, W.C.; Liu, L.T.; Zhang, Y.J.; Zhang, K.; Bai, Z.Y.; Li, A.C.; Zhu, J.J.; Li, C.D. Exogenous ethylene promotes the germination of cotton seeds under salt stress. J. Plant Growth Regul. 2023, 42, 3923–3933. [Google Scholar] [CrossRef]
  14. Cheng, B.Z.; Li, Z.; Liang, L.L.; Cao, Y.; Zeng, W.H.; Zhang, X.Q.; Ma, X.; Huang, L.K.; Nie, G.; Liu, W. The γ-aminobutyric acid (GABA) alleviates salt stress damage during seeds germination of white clover associated with Na+/K+ transportation, dehydrins accumulation, and stress-related genes expression in white clover. Int. J. Mol. Sci. 2018, 19, 2520. [Google Scholar] [CrossRef]
  15. Sousa, V.Q.; Messias, W.F.S.; Pereira, Y.C.; da Silva, B.R.S.; Lobato, E.M.S.G.; Alyemeni, M.N.; Ahmad, P.; Lobato, A.K.d.S. Pretreatment with 24-epibrassinolide synergistically protects root structures and chloroplastic pigments and upregulates antioxidant enzymes and biomass in Na+-stressed tomato plants. J. Plant Growth Regul 2021, 41, 2869–2885. [Google Scholar] [CrossRef]
  16. Wang, J.J.; Ye, W.W.; Zhou, D.Y.; LV, Y.J.; FAN, B.X.; Song, L.Y. Studies on germinationcharacteristics of diferent salinity-resistant cotton under salt stress. Cotton Sci. 2007, 19, 315–317. [Google Scholar] [CrossRef]
  17. Khan, M.O.; Irfan, M.; Muhammad, A.; Ullah, I.; Nawaz, S.; Khalil, M.K.; Ahmad, M. A practical and economical strategy to mitigate salinity stress through seed priming. Front. Environ. Sci. 2022, 10, 1–14. [Google Scholar] [CrossRef]
  18. Gupta, S.; Doležal, K.; Kulkarni, M.G.; Balázs, E.; Van Staden, J. Role of non-microbial biostimulants in regulation of seed germination and seedling establishment. Plant Growth Regul. 2022, 97, 271–313. [Google Scholar] [CrossRef]
  19. Batool, Z.; Ishfaq, M.; Akbar, N.; Zulfiqar, U.; Anjum, S.A.; Shafiq, M.; Nazir, S.; Aziz, A. Exogenous application of Atonik (sodium nitrophenolate) under skip irrigation regimes modulated the physiology, growth and productivity of Zea mays L. Arch. Agron. Soil Sci. 2023, 69, 2325–2339. [Google Scholar] [CrossRef]
  20. Swaefy, H.M.; El-Ziat, R.A. Calendula response to salinity stress. New Perspect. Agric. Crop Sci. 2020, 3, 978. [Google Scholar] [CrossRef]
  21. Mu, D.W.; Feng, N.J.; Zheng, D.F.; Zhou, H.; Liu, L.; Chen, G.J.; Mu, B.M. Physiological mechanism of exogenous brassinolide alleviating salt stress injury in rice seedlings. Sci. Rep. 2022, 12, 20439. [Google Scholar] [CrossRef] [PubMed]
  22. Wang, X.; Chai, J.L.; Liu, W.Y.; Zhu, X.L.; Liu, H.X.; Wei, X.H. Promotion of Ca2+ Accumulation in Roots by Exogenous Brassinosteroids as a Key Mechanism for Their Enhancement of Plant Salt Tolerance: A Meta-Analysis and Systematic Review. Int. J. Mol. Sci. 2023, 24, 16123. [Google Scholar] [CrossRef] [PubMed]
  23. Guo, Z.J.; Gong, J.Q.; Luo, S.T.; Zuo, Y.X.; Shen, Y.B. Role of gamma-aminobutyric acid in plant defense response. Metabolites 2023, 13, 741. [Google Scholar] [CrossRef]
  24. Alkharabsheh, H.M.; Seleiman, M.F.; Hewedy, O.A.; Battaglia, M.L.; Jalal, R.S.; Alhammad, B.A.; Schillaci, C.; Ali, N.; Al-Doss, A. Field crop responses and management strategies to mitigate soil salinity in modern agriculture: A review. Agronomy 2021, 11, 2299. [Google Scholar] [CrossRef]
  25. Hamani, A.K.M.; Wang, G.S.; Soothar, M.K.; Shen, X.J.; Gao, Y.; Qiu, R.J.; Mehmood, F. Responses of leaf gas exchange attributes, photosynthetic pigments and antioxidant enzymes in NaCl-stressed cotton (Gossypium hirsutum L.) seedlings to exogenous glycine betaine and salicylic acid. BMC Plant Biol. 2020, 20, 1–14. [Google Scholar] [CrossRef] [PubMed]
  26. Zhang, Z.G.; Li, Y.M.; Yuan, Z.; Liu, X.H.; Shu, X.Y.; Liu, J.Y.; Guo, C.F. Cotton production pattern and contribution factors in Xinjiang from 1988 to 2020. J. Agric. Resour. Environ. 2024, 1–12. [Google Scholar] [CrossRef]
  27. Zhang, Q.; Li, X.J.; Zhang, S.Y. Effects of silicon on growth andosmotic regulation of cotton seedlings under salt stress. Acta Agric. Boreali-Sin. 2019, 34, 110–117. [Google Scholar] [CrossRef]
  28. Duan, W.J.; Meng, Y.J.; Jiang, D.; Liu, L.T.; Zhang, K.; Zhang, Y.J.; Sun, H.C.; Ba, i.Z.Y.; Li, C.D. Effects of exogenous melatonin on the morphology and antioxidant enzyme activities of cotton seedlings under salt stress. Chin. J. Eco-Agric. 2022, 30, 92–104. [Google Scholar] [CrossRef]
  29. Keya, S.S.; Mostofa, M.G.; Rahman, M.M.; Das, A.K.; Sultana, S.; Ghosh, P.K.; Anik, T.R.; Ahsan, S.; Rahman, M.A.; Jahan, N. Salicylic Acid Application Improves Photosynthetic Performance and Biochemical Responses to Mitigate Saline Stress in Cotton. J. Plant Growth Regul. 2023, 42, 1–14. [Google Scholar] [CrossRef]
  30. Ahmadi, F.; Nazari, F.; Ghaderi, N.; Teixeira da Silva, J.A. Assessment of morpho-physiological and biochemical responses of perennial ryegrass to gamma-aminobutyric acid (GABA) application under salinity stress using multivariate analyses techniques. J. Plant Growth Regul. 2021, 42, 168–182. [Google Scholar] [CrossRef]
  31. Li, W.K.; Huang, B.; Li, M.L.; Wang, J.; Sun, M.T.; Yan, Y.; He, C.X.; Yu, X.C.; Li, Y.S. Studies on sodium naphthalene-1-acetate and compound sodium nitrophenolate enhancing pepper resistance to stress under intensity of sub-optimal temperature and light. China Veg. 2022, 2, 40–46. [Google Scholar] [CrossRef]
  32. Huang, B.; Li, W.K.; Sun, M.T.; Yan, Y.; Wang, J.; He, C.X.; Yu, X.C.; Li, Y.S. Effect of sodium nitrophenol on seed germination and cold tolerance of seedlings at low temperature. J. Nucl. Agric. Sci. 2022, 36, 845–855. [Google Scholar] [CrossRef]
  33. Shi, J.; Liu, D.Y.; Zhang, F.H. Physiological response and salt tolerance mechanism of cotton seedlings to salt stress. Acta Agric. Zhejiangensis 2020, 32, 1141–1148. [Google Scholar] [CrossRef]
  34. Feng, C.J.; Song, R.J.; Song, L.Y.; Zhang, S.; Qi, J.C. Effects of 2,4-epbrassinolide soaking on seed germination and physiological characteristics of Barley seedlings under drought stress. Xinjiang Agric. Sci. 2023, 60, 309–316. [Google Scholar] [CrossRef]
  35. Shu, X.; Su, X.L.; Yan, L.J.; Xiong, Y.L.; Xiong, Y.; Yu, Q.Q.; Ma, X. Effects of exogenous salicylic acid on seed germination and seedling of Elymus Sibiricus under NaCl stress. Chin. J. Grassl. 2024, 46, 87–96. [Google Scholar] [CrossRef]
  36. Ting, Z.T.; Le, L.Y.; Hong, C.; Xin, X.L.; Wei, C.X.; Heng, W.E.; Xin, Y.J. Effects of different exogenous substances on the seed germination, seedling growth, and physiology of Melilotus suaveolens under salt, alkali, and drought stress. Acta Prataculturae Sin. 2024, 33, 122–132. [Google Scholar] [CrossRef]
  37. Chen, L.; Liu, L.T.; Ma, T.T.; Jiang, D.; Sun, H.C.; Zhang, Y.J.; Zhang, K.; Bai, Z.Y.; Li, C.D. Effects of melatonin on the antioxidant enzyme activities and seed Germination of cotton (Gossypium hirsutum L.) under salt-stress conditions. Cotton Sci. 2019, 31, 438–447. [Google Scholar] [CrossRef]
  38. Muhammad, I.; Yang, L.; Ahmad, S.; Farooq, S.; Khan, A.; Muhammad, N.; Ullah, S.; Adnan, M.; Ali, S.; Liang, Q.P. Melatonin-priming enhances maize seedling drought tolerance by regulating the antioxidant defense system. Plant Physiol. 2023, 191, 2301–2315. [Google Scholar] [CrossRef]
  39. Zhang, C.; Ma, X.L.; Lu, X.F.; Li, G.; Geng, Y.S.; Sun, Y.B.; Yang, X.Y.; Geng, J.B. Effects of soil-methylpiperine on leaf physiology and root morphology of cotton seedlings under salt stress. Jiangsu Agric. Sci. 2022, 50, 81–86. [Google Scholar] [CrossRef]
  40. Fu, Y.Y.; Jiang, X.H.; Shin, X.J.; Sun, W.; Zhang, J.; Amin, A.S.; Gao, Y. The relationship between foliar K+ and Na+ concentrations and photosynthetic parameters of cotton seedlings under salt stress. Chin. J. Ecol. 2021, 40, 1716–1722. [Google Scholar] [CrossRef]
  41. Rattan, A.; Kapoor, D.; Kapoor, N.; Bhardwaj, R.; Sharma, A. Brassinosteroids regulate functional components of antioxidative defense system in salt stressed maize seedlings. J. Plant Growth Regul. 2020, 39, 1465–1475. [Google Scholar] [CrossRef]
  42. Chaudhuri, A.; Halder, K.; Abdin, M.Z.; Majee, M.; Datta, A. Abiotic stress tolerance in plants: Brassinosteroids navigate competently. Int. J. Mol. Sci. 2022, 23, 14577. [Google Scholar] [CrossRef] [PubMed]
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Figure 1. Effects of exogenous substance treatment on proline content in leaves of cotton seedlings under salt stress. Different letters indicated significant differences in the mean values of different exogenous substance treatments under the same salt stress (p < 0.05, n = 3). The vertical bar chart represents the mean ± standard deviation (SD) calculated from three repetitions. CK: distilled water, SS: 150 mmol·L−1 sodium chloride, SS+S: 150 mmol·L−1 sodium chloride + 12 mg·L−1 sodium nitrophenolate, SS+E: 150 mmol·L−1 sodium chloride + 0.15 mg·L−1 24-epibrassinolide, SS+G: 150 mmol·L−1 sodium chloride + 309.3 mg·L−1 γ-aminobutyric acid, MS: 1.2% natural saline–alkaline soil extract, MS+S: 1.2% natural saline–alkaline soil extract + 12 mg·L−1 sodium nitrophenolate, MS+E: 1.2% natural saline–alkaline soil extract + 0.15 mg·L−1 24-epibrassinolide, MS+G: 1.2% natural saline–alkaline soil extract + 309.3 mg·L−1 γ-aminobutyric acid.
Figure 1. Effects of exogenous substance treatment on proline content in leaves of cotton seedlings under salt stress. Different letters indicated significant differences in the mean values of different exogenous substance treatments under the same salt stress (p < 0.05, n = 3). The vertical bar chart represents the mean ± standard deviation (SD) calculated from three repetitions. CK: distilled water, SS: 150 mmol·L−1 sodium chloride, SS+S: 150 mmol·L−1 sodium chloride + 12 mg·L−1 sodium nitrophenolate, SS+E: 150 mmol·L−1 sodium chloride + 0.15 mg·L−1 24-epibrassinolide, SS+G: 150 mmol·L−1 sodium chloride + 309.3 mg·L−1 γ-aminobutyric acid, MS: 1.2% natural saline–alkaline soil extract, MS+S: 1.2% natural saline–alkaline soil extract + 12 mg·L−1 sodium nitrophenolate, MS+E: 1.2% natural saline–alkaline soil extract + 0.15 mg·L−1 24-epibrassinolide, MS+G: 1.2% natural saline–alkaline soil extract + 309.3 mg·L−1 γ-aminobutyric acid.
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Figure 2. Effects of exogenous substance treatment on malondialdehyde content in cotton seedling leaves under salt stress. Different letters indicated significant differences in the mean values of different exogenous substance treatments under the same salt stress (p < 0.05, n = 3). The vertical bar chart represents the mean ± standard deviation (SD) calculated from three repetitions. CK: distilled water, SS: 150 mmol·L−1 sodium chloride, SS+S: 150 mmol·L−1 sodium chloride + 12 mg·L−1 sodium nitrophenolate, SS+E: 150 mmol·L−1 sodium chloride + 0.15 mg·L−1 24-epibrassinolide, SS+G: 150 mmol·L−1 sodium chloride + 309.3 mg·L−1 γ-aminobutyric acid, MS: 1.2% natural saline–alkaline soil extract, MS+S: 1.2% natural saline–alkaline soil extract + 12 mg·L−1 sodium nitrophenolate, MS+E: 1.2% natural saline–alkaline soil extract + 0.15 mg·L−1 24-epibrassinolide, MS+G: 1.2% natural saline–alkaline soil extract + 309.3 mg·L−1 γ-aminobutyric acid.
Figure 2. Effects of exogenous substance treatment on malondialdehyde content in cotton seedling leaves under salt stress. Different letters indicated significant differences in the mean values of different exogenous substance treatments under the same salt stress (p < 0.05, n = 3). The vertical bar chart represents the mean ± standard deviation (SD) calculated from three repetitions. CK: distilled water, SS: 150 mmol·L−1 sodium chloride, SS+S: 150 mmol·L−1 sodium chloride + 12 mg·L−1 sodium nitrophenolate, SS+E: 150 mmol·L−1 sodium chloride + 0.15 mg·L−1 24-epibrassinolide, SS+G: 150 mmol·L−1 sodium chloride + 309.3 mg·L−1 γ-aminobutyric acid, MS: 1.2% natural saline–alkaline soil extract, MS+S: 1.2% natural saline–alkaline soil extract + 12 mg·L−1 sodium nitrophenolate, MS+E: 1.2% natural saline–alkaline soil extract + 0.15 mg·L−1 24-epibrassinolide, MS+G: 1.2% natural saline–alkaline soil extract + 309.3 mg·L−1 γ-aminobutyric acid.
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Figure 3. Effects of exogenous substance treatment on superoxide dismutase (A) and catalase (B) activities in cotton seedling leaves under salt stress. Different letters indicated significant differences in the mean values of different substance treatments under the same salt stress (p < 0.05, n = 3). The vertical bar chart represents the mean ± standard deviation (SD) calculated from three repetitions. CK: distilled water, SS: 150 mmol·L−1 sodium chloride, SS+S: 150 mmol·L−1 sodium chloride + 12 mg·L−1 sodium nitrophenolate, SS+E: 150 mmol·L−1 sodium chloride + 0.15 mg·L−1 24-epibrassinolide, SS+G: 150 mmol·L−1 sodium chloride + 309.3 mg·L−1 γ-aminobutyric acid, MS: 1.2% natural saline–alkaline soil extract, MS+S: 1.2% natural saline–alkaline soil extract + 12 mg·L−1 sodium nitrophenolate, MS+E: 1.2% natural saline–alkaline soil extract + 0.15 mg·L−1 24-epibrassinolide, MS+G: 1.2% natural saline–alkaline soil extract + 309.3 mg·L−1 γ-aminobutyric acid.
Figure 3. Effects of exogenous substance treatment on superoxide dismutase (A) and catalase (B) activities in cotton seedling leaves under salt stress. Different letters indicated significant differences in the mean values of different substance treatments under the same salt stress (p < 0.05, n = 3). The vertical bar chart represents the mean ± standard deviation (SD) calculated from three repetitions. CK: distilled water, SS: 150 mmol·L−1 sodium chloride, SS+S: 150 mmol·L−1 sodium chloride + 12 mg·L−1 sodium nitrophenolate, SS+E: 150 mmol·L−1 sodium chloride + 0.15 mg·L−1 24-epibrassinolide, SS+G: 150 mmol·L−1 sodium chloride + 309.3 mg·L−1 γ-aminobutyric acid, MS: 1.2% natural saline–alkaline soil extract, MS+S: 1.2% natural saline–alkaline soil extract + 12 mg·L−1 sodium nitrophenolate, MS+E: 1.2% natural saline–alkaline soil extract + 0.15 mg·L−1 24-epibrassinolide, MS+G: 1.2% natural saline–alkaline soil extract + 309.3 mg·L−1 γ-aminobutyric acid.
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Figure 4. Effects of exogenous substance treatment on Cl− (A), Na+ (B), K+ (C) and K+/Na+ (D) in cotton seedlings under salt stress. Different letters indicated significant differences in the mean values of different exogenous substance treatments under the same salt stress (p < 0.05, n = 3). The vertical bar chart represents the mean ± standard deviation (SD) calculated from three repetitions. CK: distilled water, SS: 150 mmol·L−1 sodium chloride, SS+S: 150 mmol·L−1 sodium chloride + 12 mg·L−1 sodium nitrophenolate, SS+E: 150 mmol·L−1 sodium chloride + 0.15 mg·L−1 24-epibrassinolide, SS+G: 150 mmol·L−1 sodium chloride + 309.3 mg·L−1 γ-aminobutyric acid, MS: 1.2% natural saline–alkaline soil extract, MS+S: 1.2% natural saline–alkaline soil extract + 12 mg·L−1 sodium nitrophenolate, MS+E: 1.2% natural saline–alkaline soil extract + 0.15 mg·L−1 24-epibrassinolide, MS+G: 1.2% natural saline–alkaline soil extract + 309.3 mg·L−1 γ-aminobutyric acid.
Figure 4. Effects of exogenous substance treatment on Cl− (A), Na+ (B), K+ (C) and K+/Na+ (D) in cotton seedlings under salt stress. Different letters indicated significant differences in the mean values of different exogenous substance treatments under the same salt stress (p < 0.05, n = 3). The vertical bar chart represents the mean ± standard deviation (SD) calculated from three repetitions. CK: distilled water, SS: 150 mmol·L−1 sodium chloride, SS+S: 150 mmol·L−1 sodium chloride + 12 mg·L−1 sodium nitrophenolate, SS+E: 150 mmol·L−1 sodium chloride + 0.15 mg·L−1 24-epibrassinolide, SS+G: 150 mmol·L−1 sodium chloride + 309.3 mg·L−1 γ-aminobutyric acid, MS: 1.2% natural saline–alkaline soil extract, MS+S: 1.2% natural saline–alkaline soil extract + 12 mg·L−1 sodium nitrophenolate, MS+E: 1.2% natural saline–alkaline soil extract + 0.15 mg·L−1 24-epibrassinolide, MS+G: 1.2% natural saline–alkaline soil extract + 309.3 mg·L−1 γ-aminobutyric acid.
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Figure 5. Principal component biplots of exogenous substance treatment under single-salt (A) and mixed-salt (B) stresses. X1: height, X2: root dry weight, X3: stem dry weight, X4: leaf dry weight, X5: malondialdehyde, X6: superoxide dismutase, X7: catalase, X8: proline, X9: root Na+, X10: stem Na+, X11: leaf Na+, X12: root K+, X13: stem K+, X14: leaf K+, X15: root Cl−, X16: stem Cl−, X17: leaf Cl−. CK: distilled water, SS: 150 mmol·L−1 sodium chloride, SS+S: 150 mmol·L−1 sodium chloride + 12 mg·L−1 sodium nitrophenolate, SS+E: 150 mmol·L−1 sodium chloride + 0.15 mg·L−1 24-epibrassinolide, SS+G: 150 mmol·L−1 sodium chloride + 309.3 mg·L−1 γ-aminobutyric acid, MS: 1.2% natural saline–alkaline soil extract, MS+S: 1.2% natural saline–alkaline soil extract + 12 mg·L−1 sodium nitrophenolate, MS+E: 1.2% natural saline–alkaline soil extract + 0.15 mg·L−1 24-epibrassinolide, MS+G: 1.2% natural saline–alkaline soil extract + 309.3 mg·L−1 γ-aminobutyric acid.
Figure 5. Principal component biplots of exogenous substance treatment under single-salt (A) and mixed-salt (B) stresses. X1: height, X2: root dry weight, X3: stem dry weight, X4: leaf dry weight, X5: malondialdehyde, X6: superoxide dismutase, X7: catalase, X8: proline, X9: root Na+, X10: stem Na+, X11: leaf Na+, X12: root K+, X13: stem K+, X14: leaf K+, X15: root Cl−, X16: stem Cl−, X17: leaf Cl−. CK: distilled water, SS: 150 mmol·L−1 sodium chloride, SS+S: 150 mmol·L−1 sodium chloride + 12 mg·L−1 sodium nitrophenolate, SS+E: 150 mmol·L−1 sodium chloride + 0.15 mg·L−1 24-epibrassinolide, SS+G: 150 mmol·L−1 sodium chloride + 309.3 mg·L−1 γ-aminobutyric acid, MS: 1.2% natural saline–alkaline soil extract, MS+S: 1.2% natural saline–alkaline soil extract + 12 mg·L−1 sodium nitrophenolate, MS+E: 1.2% natural saline–alkaline soil extract + 0.15 mg·L−1 24-epibrassinolide, MS+G: 1.2% natural saline–alkaline soil extract + 309.3 mg·L−1 γ-aminobutyric acid.
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Table 1. pH value, mineralization degree, and eight ion content of high-salt solution.
Table 1. pH value, mineralization degree, and eight ion content of high-salt solution.
TitleUnitHigh-Salt Solution
pH—8.61
Salinityg·kg−1272.1
Electrical conductivityS·m−16.772
HCO3−g·kg−10.3942
Cl−g·kg−1109.0058
SO42−g·kg−179.6118
Ca2+g·kg−12.4125
Mg2+g·kg−12.2074
K+g·kg−10.4705
Na+g·kg−137.15
Table 2. Effects of exogenous substance treatment on plant height and biomass of cotton seedlings under salt stress.
Table 2. Effects of exogenous substance treatment on plant height and biomass of cotton seedlings under salt stress.
TreatmentHeight
(cm)		Root Dry Weight (mg·plant−1)Stem Dry Weight (mg·plant−1)Leaf Dry Weight (mg·plant−1)
CK7.2 ± 0.3 a86.7 ± 18.5 a165.1 ± 21 a155.3 ± 23 a
SS6.2 ± 0.2 b37.7 ± 17.8 b156.6 ± 28.8 a108.3 ± 20 b
SS+S7.1 ± 0.4 a48.7 ± 17.5 ab162.3 ± 15.9 a119.8 ± 20.8 ab
SS+E6.9 ± 0.1 a40.9 ± 19.4 b159.9 ± 17.8 a125.4 ± 24.5 ab
SS+G7.1 ± 0.5 a58.4 ± 21.3 ab162.2 ± 18.4 a132.6 ± 17.9 ab
CK7.2 ± 0.3 a86.8 ± 18.5 a165.1 ± 21 a155.3 ± 23 a
MS6.3 ± 0.2 b51.8 ± 20.3 a160.7 ± 25.3 a133.7 ± 21.5 a
MS+S7 ± 0.2 a57.8 ± 20.1 a163.7 ± 23.6 a137.4 ± 27.3 a
MS+E6.8 ± 0.2 a54.4 ± 17.2 a161.2 ± 22.2 a137.4 ± 26.2 a
MS+G7.2 ± 0.3 a69 ± 18 a163.2 ± 18.9 a141.6 ± 18.6 a
Note: Different letters indicated significant differences in the mean values of different exogenous substance treatments under the same salt stress (p < 0.05, n = 3). The data are presented as means ± standard deviation (SD) calculated from three repetitions. CK: distilled water, SS: 150 mmol·L−1 sodium chloride, SS+S: 150 mmol·L−1 sodium chloride + 12 mg·L−1 sodium nitrophenolate, SS+E: 150 mmol·L−1 sodium chloride + 0.15 mg·L−1 24-epibrassinolide, SS+G: 150 mmol·L−1 sodium chloride + 309.3 mg·L−1 γ-aminobutyric acid, MS: 1.2% natural saline–alkaline soil extract, MS+S: 1.2% natural saline–alkaline soil extract + 12 mg·L−1 sodium nitrophenolate, MS+E: 1.2% natural saline–alkaline soil extract + 0.15 mg·L−1 24-epibrassinolide, MS+G: 1.2% natural saline–alkaline soil extract + 309.3 mg·L−1 γ-aminobutyric acid.
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MDPI and ACS Style

Dong, Z.; Meng, A.; Qi, T.; Huang, J.; Yang, H.; Tayir, A.; Wang, B. Exogenous Substances Improved Salt Tolerance in Cotton. Agronomy 2024, 14, 2098. https://doi.org/10.3390/agronomy14092098

AMA Style

Dong Z, Meng A, Qi T, Huang J, Yang H, Tayir A, Wang B. Exogenous Substances Improved Salt Tolerance in Cotton. Agronomy. 2024; 14(9):2098. https://doi.org/10.3390/agronomy14092098

Chicago/Turabian Style

Dong, Zhiduo, Ajing Meng, Tong Qi, Jian Huang, Huicong Yang, Aziguli Tayir, and Bo Wang. 2024. "Exogenous Substances Improved Salt Tolerance in Cotton" Agronomy 14, no. 9: 2098. https://doi.org/10.3390/agronomy14092098

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