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The γ-aminobutyric acid (GABA) is a widely distributed neurotransmitter in living organisms, known for its inhibitory role in animals. GABA exerts calming effects on the mind, lowers blood pressure in animals, and enhances stress resistance during the growth and development of plants. Enhancing GABA content in plants has become a focal point of current research. In plants, GABA is synthesized through two metabolic pathways, the GABA shunt and the polyamine degradation pathway, with the GABA shunt being the primary route. Extensive studies have investigated the regulatory mechanisms governing GABA synthesis. At the genetic level, GABA production and degradation can be modulated by gene overexpression, signaling molecule-induced expression, transcription factor regulation, and RNA interference. Additionally, at the level of transporter proteins, increased activity of GABA transporters and proline transporters enhances the transport of glutamate and GABA. The activity of glutamate decarboxylase, a key enzyme in GABA synthesis, along with various external factors, also influences GABA synthesis. This paper summarizes the biological functions, metabolic pathways, and regulatory mechanisms of GABA, providing a theoretical foundation for further research on GABA in plants. [ABSTRACT FROM AUTHOR]

The γ-aminobutyric acid (GABA) is a widely distributed neurotransmitter in living organisms, known for its inhibitory role in animals. GABA exerts calming effects on the mind, lowers blood pressure in animals, and enhances stress resistance during the growth and development of plants. Enhancing GABA content in plants has become a focal point of current research. In plants, GABA is synthesized through two metabolic pathways, the GABA shunt and the polyamine degradation pathway, with the GABA shunt being the primary route. Extensive studies have investigated the regulatory mechanisms governing GABA synthesis. At the genetic level, GABA production and degradation can be modulated by gene overexpression, signaling molecule-induced expression, transcription factor regulation, and RNA interference. Additionally, at the level of transporter proteins, increased activity of GABA transporters and proline transporters enhances the transport of glutamate and GABA. The activity of glutamate decarboxylase, a key enzyme in GABA synthesis, along with various external factors, also influences GABA synthesis. This paper summarizes the biological functions, metabolic pathways, and regulatory mechanisms of GABA, providing a theoretical foundation for further research on GABA in plants.

The effect of exogenous γ-aminobutyric acid (GABA) and GABA synthesis inhibitor 3-mercaptopropionic acid (3-MP) on GABA metabolism and quality in fresh-cut pumpkin was investigated, and the possible mechanism was studied. The results indicated that exogenous GABA induced the accumulation of endogenous GABA and promoted the conversion of glutamic acid to GABA in fresh-cut pumpkin through the catalytic conversion of highly active glutamate decarboxylase (GAD). The 3-MP-treated pumpkin retained lower GABA content than the control, and the activities of GAD and GABA transaminase (GABA-T) were inhibited. The GABA-treated pumpkins possessed relatively lower polyamines (putrescine, spermine and spermidine) contents in comparison with the control during storage. 3-MP treatment restrained the activities of polyamine oxidase (PAO), diamine oxidase (DAO) and amino aldehyde decarboxylase (AMADH). These results demonstrated that GABA treatment could activate the polyamine degradation pathway and promote GABA enrichment in pumpkin. Meanwhile, no significant differences in maximum colony count, color, β-carotene content and soluble solids content were observed among treatments during storage, which suggested that exogenous GABA had little effect on the quality of fresh-cut pumpkin.

Effect of fresh-cut procedure on the accumulation of GABA in carrots via γ-aminobutyric acid (GABA) shunt and polyamines degradation pathway was investigated. Results showed that fresh-cut processing enhanced glutamate decarboxylase (GAD) activity and expression levels of DcGAD1 and DcGAD2, while reduced GABA transaminase (GABA-T) activity and DcGABA-T1 expression level, which induced the more glutamate (Glu) conversion to GABA. Polyamines (PAs) in shredded carrots were significantly lower than the whole, due to the elevated activities of diamine oxidase (DAO), polyamine oxidase (PAO) and aminoaldehyde dehydrogenase (AMADH) and DcPAO expression level, which indicated that the polyamines degradation pathway was activated and more PAs were converted to GABA. These results suggested that fresh-cut procedure can induce the accumulation of GABA through activating GABA shunt and polyamines degradation pathway. Besides, fresh-cut processing treatment did not have much adverse effect on the organoleptic quality of carrots. [ABSTRACT FROM AUTHOR]

Highlights • CaCl 2 treatment stimulated a rapid accumulation of GABA in shredded carrots. • A dramatic increase in GABA content was observed in AsA-treated shredded carrots. • GABA accumulated through activating GABA shunt and polyamines degradation pathway. Abstract CaCl 2 or AsA treatment was applied to shredded carrots to explore their influences on GABA content and its metabolic pathway. The metabolites, enzyme activity and gene expression associated with GABA shunt pathway and polyamine degradation were measured. Results demonstrated that treatment with exogenous CaCl 2 or AsA alone not only significantly promoted the activities of glutamate decarboxylase (GAD), GABA transaminase (GABA-T), diamine oxidase (DAO), polyamine oxidase (PAO) and aminoaldehyde dehydrogenase (AMADH), but up-regulated the expressions of DcGAD 1, DcGAD 2, DcGABA-T 1 and DcPAO. Meanwhile, glutamate (Glu) content, a substrate for GABA shunt, was significantly reduced in both two exogenous treatments. In addition, lower putrescine (Put) and spermine (Spm) contents were observed in AsA treatment only. Taken together, our results suggested that both CaCl 2 and AsA treatments could activate GABA shunt pathway and polyamine degradation. CaCl 2 seemed to be more effective to GABA shunt regulation, while AsA to polyamine degradation. [ABSTRACT FROM AUTHOR]

The γ-aminobutyric acid (GABA) is a non-protein amino acid with some functional properties for human health. Its content is usually lower in plant seeds. Hypoxia or salt (NaCl) stress is an effective way for accumulating GABA during seed germination. However, NaCl stress on GABA accumulation under hypoxia is currently infrequent. The effect of NaCl on GABA accumulation in germinating faba bean (Vicia faba L.) under hypoxia was therefore investigated in this study. Faba bean seeds were steeped in citric acid buffer (pH 3.5) containing NaCl with a final O2 concentration of 5.5 mg L-1 and germinated for 5 d. Results showed that 60 mmol L-1 NaCl was the optimum concentration for GABA accumulation in germinating faba beans under hypoxia. Germination for 5 d under hypoxia-NaCl stress was less beneficial for GABA accumulation than only hypoxia (control). Polyamine degradation pathway played a more important role for accumulating GABA in germinating faba bean as an adaptive response to NaCl stress. Removing NaCl significantly increased GABA content, while it decreased glutamate decarboxylase (GAD) activity. Simultaneously, polyamine was accumulated, which might be related to the enhancement of physiological activity after recovery. When treated with aminoguanidine (AG) for 3 d, GABA content decreased by 29.82%. These results indicated that the tolerance ability of GABA shunt to NaCl stress was weaker than that of polyamine degradation pathway. The NaCl treatment for 3 d under hypoxia could raise the contribution ratio of polyamine degradation pathway for GABA accumulation. The contribution ratio of polyamine degradation pathway for GABA formation was 29.82% when treated for at least 3 d. [ABSTRACT FROM AUTHOR]

Effects of calcium on soybean growth and gamma-aminobutyric acid (GABA) accumulation pathways in germinating soybean were investigated. The harmful effect of NaCl stress was alleviated by CaCl while was aggravated by LaCl. Glutamate decarboxylase (GAD) activity increased significantly under NaCl plus CaCl treatment, while its gene expression levels had no significant changes compared with NaCl treatment. GAD and diamine oxidase (DAO) activities and their gene expression levels significantly decreased after LaCl was applied. When treated with AG, the soybean growth was suppressed and DAO activity was inhibited completely while DAO expression had no significant changes. Meanwhile, the GABA content decreased by 17.04 and 11.76 % in cotyledon and embryo under NaCl plus CaCl treatment compared with NaCl treatment, respectively. It can be concluded that CaCl addition changed the contribution ratio of GABA shunt and polyamine degradation pathway for GABA formation, and the increment of GABA in germinating soybean was mainly synthesized via GABA shunt. [ABSTRACT FROM AUTHOR]

Effects of NaCl stress and supplemental CaCl on soybean growth and gamma-aminobutyric acid (GABA) accumulation pathways in germinating soybean were investigated. Germinating under NaCl stress, GABA accumulation was caused not only by the activation of glutamate decarboxylase (GAD), diamine oxidase (DAO) and aminoaldehyde dehydrogenase (AMADH) existing in seed but also by their gene expression up-regulation during germination. However, after CaCl (6 mM) application, the harmful effect of NaCl stress (50 mM) was removed. GAD activity significantly increased, while its gene expression levels had no significant changes with the control, indicating that the increment in GAD activity was caused by the stimulation of exogenous Ca. Meanwhile, GABA was still accumulated although DAO and AMADH activities and their gene expression levels had no significant difference compared with the control. It can be concluded that CaCl addition decreased the contribution of polyamine degradation pathway to GABA accumulation compared with NaCl stress, and the increased GABA was mainly synthesized via GABA shunt. [ABSTRACT FROM AUTHOR]

• CaCl 2 treatment stimulated a rapid accumulation of GABA in fresh-cut pears. • LaCl 3 reduced GABA by inhibition of GABA shunt and polyamine degradation pathway. • CaCl 2 increased GABA content via GABA shunt rather than polyamine degradation. Effect of calcium chloride (CaCl 2) on γ-aminobutyric acid (GABA) accumulation pathways in fresh-cut pears was investigated. The metabolites, enzyme activity and gene expression associated with GABA shunt and polyamine degradation were measured. Results demonstrated that CaCl 2 treatment promoted GABA accumulation and reduced the glutamate (Glu) content in fresh-cut pears. Ca2+ fluorescence in pear cell, glutamate decarboxylase (GAD) activity and its gene expression increased significantly under CaCl 2 treatment correspondingly. Meanwhile, the Ca2+ channel blockers lanthanum chloride (LaCl 3) treatment not only significantly inhibited the activities of GAD, GABA transaminase (GABA-T), diamine oxidase (DAO), polyamine oxidase (PAO) and aminoaldehyde dehydrogenase (AMADH), but also down-regulated the transcripts of PbGAD , PbGABA-T , PbPAO1 and PbPAO2. Taken together, it can be concluded that CaCl 2 seems to be more effective to GABA shunt, while LaCl 3 treatment mightily stimulate GABA shunt and polyamine degradation pathway. [ABSTRACT FROM AUTHOR]