Gamma-aminobutyric acid (GABA) alleviates salt damage in tomato by modulating Na+ uptake, the GAD gene, amino acid synthesis and reactive oxygen species metabolism

Abstract

Background: Salt stress is a serious abiotic stress that caused crop growth inhibition and yield decline. Previous studies have reported on the the synthesis of gamma-aminobutyric acid (GABA) and its relationship with plant resistance under various abiotic stress. However, the relationship between exogenous GABA alleviating plant salt stress damage and ion flux, amino acid synthesis, and key enzyme expression remains largely unclear. We investigated plant growth, Na+ transportation and accumulation, reactive oxygen species (ROS) metabolism and evaluated the effect of GABA on amino acids especially SlGADs gene expression and the endogenous GABA content of tomato (Solanum lycopersicum L.) seedlings treated with or without 5 mmol·L-1 GABA under 175 mmol·L-1 NaCl stress. Results: Exogenous application of GABA significantly reduced the salt damage index and increased plant height, chlorophyll content and the dry and fresh weights of tomato plants exposed to NaCl stress. GABA significantly reduced Na+ accumulation in leaves and roots by preventing Na+ influx in roots and transportation to leaves. The transcriptional expression of SlGAD1-3 genes were induced by NaCl stress especially with GABA application. Among them, SlGAD1 expression was the most sensitive and contributed the most to the increase in glutamic acid decarboxylase (GAD) activity induced by NaCl and GABA application; Exogenous GABA increased GAD activity and amino acid contents in tomato leaves compared with the levels under NaCl stress alone, especially the levels of endogenous GABA, proline, glutamate and eight other amino acids. These results indicated that SlGADs transcriptional expression played an important role in tomato plant resistance to NaCl stress with GABA application by enhancing GAD activity and amino acid content. GABA significantly alleviated the active oxygen-related injury of leaves under NaCl stress by increasing the activities of antioxidant enzymes and decreasing the contents of active oxygen species and malondialdehyde.Conclusion: Exogenous GABA had a positive effect on the resistance of tomato seedlings to salt stress, which was closely associated with reducing Na+ flux from root to leaves, increasing amino acid content and strengthening antioxidant metabolism. Endogenous GABA content was induced by salt and exogenous GABA at both the transcriptional and metabolic levels.

Transcriptome changes induced by Arbuscular mycorrhizal symbiosis in leaves of durum wheat (Triticum durum Desf.) promote higher salt tolerance

“…CATs are involved in the enzymatic response to ROS 40 , GSTs reduce oxidative stress by affecting glutathione pools 41,42 , while CYP genes are known to provide tolerance to salinity and other abiotic stresses by influencing ROS scavenging and ABA levels 43 . Both GABA and glutamate metabolism and catabolism were also reported to play a key role in the response to salt stress by controlling ROS accumulation and regulating redox balance 44,45 . Interestingly, in AM + plants, we detected a significant downregulation of two glutamate or Glutamic Acid Decarboxylase (GAD) enzymes involved in the synthesis of GABA from L-glutamate as well as a GABA-T involved in the conversion of GABA to succinic semialdehyde (SSA), already reported to be induced by salt stress in Arabidopsis and maize 46,47 .…”

Tomato salt tolerance mechanisms and their potential applications for fighting salinity: A review

“…Foliar application of L-methionine (Met) and L-phenylalanine (Phe) induces salt tolerance of tomato by enhancing the PM stability, the contents of osmolytes, and the activity of antioxidative enzymes (Almas et al, 2021). Under salt stress, exogenous GABA inducing amino acid content increases osmotic adjustment capacity to resist water loss and neutralizes excessive Na + in the vacuoles in tomato leaves (Wu et al, 2020). Trehalose alleviates the salt damage of tomato plants by promoting the accumulation of osmotic substances Pro, GB, and soluble proteins (Yang Y. et al, 2022).…”

“…Gamma-aminobutyric acid metabolic pathway, also known as GABA shunt, is probably involved in salt tolerance of tomato by modulating amino acid synthesis and ROS metabolism. Exogenous GABA has positive effects on alleviating salt stress, which is mainly due to induced osmotic regulation and antioxidant metabolism by the salt-and exogenous GABAinduced endogenous GABA (Wu et al, 2020; Figure 2). In GABA shunt, glutamate decarboxylase (GAD) catalyzes the decarboxylation of glutamate to GABA, GABA transaminase (GABA-T) converts GABA to succinic semialdehyde (SSA), and SSA dehydrogenase (SSADH) catalyzes the oxidation of SSA to succinate.…”

Exogenous calcium application enhances salt tolerance of sweet sorghum seedlings

“…Under salt stress, exogenous GABA can increase the content of proline and soluble sugar, reduce the content of O 2 −• and MDA and thus enhance the salt tolerance of maize (Wang et al, 2017). Applying GABA to tomato under salt stress not only increases amino acid content and enhance antioxidant activity but also reduces Na + flux from root to leaf (Wu et al, 2020). Therefore, SbGADX1 may also enhance the salt tolerance of sweet sorghum by regulating GABA to enhance intracellular osmotic potential and accelerate ROS clearance.…”