1. Introduction
Soil salinization is a major abiotic stress limiting agricultural productivity worldwide, particularly in coastal and irrigated regions. Rice as a salt-sensitive crop, is highly vulnerable to elevated salinity levels, especially during seedling and reproductive stages.
Salt stress imposes both osmotic stress and ionic toxicity, resulting in impaired physiological metabolism, oxidative damage, and ultimately yield reduction.
Recent studies have demonstrated that exogenous application of γ-aminobutyric acid (GABA) and betaine (glycine betaine) can significantly enhance plant tolerance to salinity stress. Their combined application has attracted increasing attention due to potential synergistic effects on plant physiological regulation.
2. Physiological Constraints of Rice Under Salt Stress
Salt stress affects rice growth through multiple pathways:
2.1 Osmotic Stress
High salt concentration in the rhizosphere reduces soil water potential, limiting water uptake and causing physiological drought.
2.2 Ionic Toxicity
Excessive accumulation of Na⁺ and Cl⁻ leads to:
- Disruption of intracellular ion homeostasis
- Competitive inhibition of K⁺ uptake
- Enzyme inactivation and metabolic disorder
2.3 Oxidative Stress
Salt stress induces overproduction of reactive oxygen species (ROS) such as:
- Superoxide anion (O₂⁻)
- Hydrogen peroxide (H₂O₂)
These ROS cause:
- Lipid peroxidation (increased MDA content)
- Membrane damage
- Protein and nucleic acid degradation
2.4 Photosynthetic Inhibition
- Decreased chlorophyll content
- Reduced stomatal conductance
- Impaired photosystem II efficiency
3. Role of GABA in Enhancing Salt Tolerance
GABA is a non-protein amino acid widely involved in plant stress responses and metabolic regulation.
3.1 Regulation of Carbon–Nitrogen Metabolism
GABA participates in the GABA shunt, linking carbon and nitrogen metabolism, thereby maintaining metabolic balance under stress.
3.2 Enhancement of Antioxidant Defense System
Exogenous GABA significantly increases the activity of antioxidant enzymes:
- Superoxide dismutase (SOD)
- Catalase (CAT)
- Peroxidase (POD)
This leads to effective scavenging of ROS and reduction of oxidative damage.
3.3 Maintenance of Membrane Integrity
GABA reduces malondialdehyde (MDA) accumulation and stabilizes membrane structures, improving cell viability under stress.
3.4 Regulation of Ion Transport
GABA contributes to:
- Reduced Na⁺ uptake
- Improved K⁺ retention
- Better Na⁺/K⁺ homeostasis
4. Role of Betaine in Salt Stress Mitigation
Betaine is a well-known compatible solute (osmoprotectant) that accumulates in plants under stress.
4.1 Osmotic Adjustment
Betaine helps maintain cellular turgor by:
- Balancing osmotic pressure
- Enhancing water retention capacity
4.2 Protection of Photosynthetic Apparatus
Betaine stabilizes:
- Chloroplast membrane structure
- Photosystem II (PSII)
- Rubisco enzyme activity
Thus improving photosynthetic efficiency under saline conditions.
4.3 Stabilization of Proteins and Enzymes
Betaine protects macromolecules from denaturation caused by ionic and osmotic stress.
4.4 Reduction of Oxidative Damage
It indirectly enhances antioxidant capacity and reduces ROS accumulation.
5. Synergistic Mechanisms of GABA and Betaine
The combined application of GABA and betaine results in multi-level physiological enhancement, showing stronger effects than individual treatments.
5.1 Integrated Stress Regulation
- GABA: metabolic regulation + ROS scavenging
- Betaine: osmotic balance + structural protection
👉 Together they provide complementary stress resistance pathways
5.2 Enhanced Antioxidant Capacity
- Higher SOD, CAT, POD activities
- Lower MDA and H₂O₂ levels
- Reduced membrane lipid peroxidation
5.3 Improved Ion Homeostasis
- Decreased Na⁺ accumulation in shoots
- Increased K⁺ retention
- Optimized Na⁺/K⁺ ratio
5.4 Promotion of Growth and Yield Formation
Combined treatment leads to:
- Increased root activity and nutrient uptake
- Improved tillering capacity
- Enhanced grain filling rate
- Higher 1000-grain weight
Ultimately resulting in significant yield improvement under saline conditions
6. Agronomic Application and Recommendations
6.1 Application Method
- Foliar spray (most effective)
- Can be combined with fertigation systems
6.2 Application Stages
- Seedling stage (stress prevention)
- Tillering stage (growth enhancement)
- Booting stage (yield protection)
6.3 General Dosage Range (for formulation reference)
- GABA: 10–50 mg/L
- Betaine: 100–300 mg/L
(Exact dosage should be optimized based on formulation and local conditions)
7. Practical Significance
The combined use of GABA and betaine provides a scientifically validated strategy for:
- Improving salt tolerance in rice
- Stabilizing yield in saline soils
- Enhancing fertilizer use efficiency
- Supporting sustainable agriculture
This approach is particularly suitable for:
- Coastal saline-alkali soils
- Irrigated areas with secondary salinization
- High-value crop production systems
8. Conclusion
The synergistic application of GABA and betaine represents an effective biostimulant strategy for mitigating salt stress in rice.
By integrating metabolic regulation, osmotic adjustment, antioxidant defense, and ion homeostasis, this combination significantly improves plant physiological performance and yield stability under saline conditions.
