GABA-transaminase Activity Research Articles

Enhanced accumulation of γ-aminobutyric acid by deletion of aminotransferase genes involved in γ-aminobutyric acid catabolism in engineered Halomonas elongata.

In this study, we were able to increase the yield of GABA by 1.5 times in the GABA-producing H. elongata ZN3 strain by deleting the gabT gene, which encodes GABA-AT, the initial enzyme of the GABA catabolic pathway. We also report the first in vivo evidence for GABA aminotransferase activity of an ectB-encoded DABA-AT, confirming a longstanding speculation based on the reported in vitro GABA-AT activity of DABA-AT. According to our findings, the DABA-AT enzyme can catalyze the initial step of GABA catabolism, in addition to its known function in ectoine biosynthesis. This creates a cycle that promotes adequate substrate flow between the two pathways, particularly during the early stages of high-salinity stress response when the expression of the ectB gene is upregulated.

Regulation and mechanism of enzyme metabolism in germinated hemp seeds by ultrasound combined with exogenous calcium chloride treatment

γ-aminobutyric acid (GABA) plays an important role in anti-anxiety by inhibiting neurotransmitter in the central nervous system (CNS) of mammals, which is generated in the germinating seeds. The key enzymes activity of GABA metabolism pathway and nutrients content in hemp seeds during germination were studied after treated with ultrasound and CaCl2. The mechanism of exogenous stress on key enzymes in GABA metabolism pathway was investigated by molecular dynamics simulation. The results showed that ultrasonic combined with 1.5 mmol·L−1CaCl2 significantly increased the activities of glutamate decarboxylase (GAD) and GABA transaminase (GABA-T) in seeds, and promoted the conversion of glutamate to GABA, resulting in the decrease of glutamate content and the accumulation of GABA. Molecular dynamics simulations revealed that Ca2+ environment enhanced the activity of GAD and GABA-T enzymes by altering their secondary structure, exposing their hydrophobic residues. Ultrasound, germination and CaCl2 stress improved the nutritional value of hemp seeds.

Is hepatic GABA transaminase a promising target for obesity and epilepsy treatments?

γ-Aminobutyric acid (GABA) transaminase (GABA-T) is a GABA-degrading enzyme that plays an essential role in regulating GABA levels and maintaining supplies of GABA. Although GABA in the mammalian brain was discovered 70 years ago, research on GABA and GABA-T has predominantly focused on the brain. Notwithstanding the high activity and expression of GABA-T in the liver, the exact functions of GABA-T in the liver remain unknown. This article reviews the up-to-date information on GABA-T in the liver. It presents recent findings on the role of liver GABA-T in food intake suppression and appetite regulation. Finally, the potential functions of liver GABA-T in other neurological diseases, natural GABA-T inhibitors, and future perspectives in this research area are discussed.

GABA-transaminase: A Key Player and Potential Therapeutic Target for Neurological Disorders.

Neurological disorders such as epilepsy, autism, Huntington's disease, multiple sclerosis, and Alzheimer's disease alter brain functions like cognition, mood, movements, and language, severely compromising the well-being of persons, suffering from their negative effects. The neurotransmitters (GABA, glutamate, norepinephrine, dopamine) are found to be involved in neuronal signaling and neurotransmission. GABA, a "commanding neurotransmitter" is directly or indirectly associated with various neurological disorders. GABA is metabolized to succinic semialdehyde by a mitochondrial gamma-aminobutyric acid-transaminase (GABA-T) enzyme. Therefore, the alterations in the GABA performance in the distinct regions of the brain via GABA-T overstimulation or inhibition would play a vital role in the pathogenesis of various neurological disorders. This review emphasizes the leading participation of GABA-T in neurological disorders like Huntington's disease, epilepsy, autism, Alzheimer's disease, and multiple sclerosis. In Huntington's disease, epilepsy, and multiple sclerosis, the surfeited performance of GABA-T results in diminished levels of GABA, whereas in autism, the subsidence of GABA-T activity causes the elevation in GABA contents, which is responsible for behavioral changes in these disorders. Therefore, GABA-T inhibitors (in Huntington's disease, epilepsy, and multiple sclerosis) or agonists (in autism) can be used therapeutically. In the context of Alzheimer's disease, some researchers favor the stimulation of GABA-T activity whereas some disagree with it. Therefore, the activity of GABA-T concerning Alzheimer's disease is still unclear. In this way, studies of GABA-T enzymatic activity in contrast to neurological disorders could be undertaken to understand and be considered a therapeutic target for several GABA-ergic CNS diseases.

Drought priming-induced stress memory improves subsequent drought or heat tolerance via activation of γ-aminobutyric acid-regulated pathways in creeping bentgrass.

Recurrent drought can induce stress memory in plants to induce tolerance to subsequent stress, such as high temperature or drought. Drought priming (DP) is an effective approach to improve tolerance to various stresses; however, the potential mechanism of DP-induced stress memory has not been fully resoved. We examined DP-regulated subsequent drought tolerance or thermotolerance associated with changes in physiological responses, GABA and NO metabolism, heat shock factor(HSF) and dehydrin (DHN) pathways in perennial creeping bentgrass. Plants can recover after two cycle of DP, and DP-treated plants had significantly higher tolerance to subsequent drought or heat stress, with higher leaf RWC, Chl content, photochemical efficiency, and cell membrane stability. DP significantly alleviated oxidative damage through enhancing total antioxidant capacity in response to subsequent drought or heat stress. Endogenous GABA was significantly increased by DP through activating glutamic acid decarboxylase activity and inhibiting GABA transaminase activity. DP also enhanced accumulation of NO, depending on NOS activity, under subsequent drought or heat stress. Transcript levels of multiple transcription factors, heat shock proteins, and DHNs in the HSF and DHN pathways were up-regulated by DP under drought or heat stress, but there were differences between DP-regulated heat tolerance and drought tolerance in these pathways. The findings indicate that under recurrent moderate drought, DP improves subsequent tolerance to drought or heat stress in relation to GABA-regulated pathways, providing new insight into understanding of the role of stress memory in plant adaptation to complex environmental stresses.

Anxiolytic effects of Dichrocephala integrifolia leaf aqueous extract on alcohol withdrawal-induced anxiety in mice: Involvement of the GABAergic pathway

Ethanol withdrawal syndrome is a life-threatening state that results from a sudden termination of chronic alcohol intake. One of the manifestations of ethanol withdrawal syndrome is anxiety. Dichrocephala integrifolia is a plant used in Africa in the treatment of alcohol use disorders. This study aimed to evaluate the effects of Dichrocephala integrifolia on ethanol withdrawal anxiety in mice. Young adult Swiss mice were arranged into seven groups of six mice each. Groups II to VII received ethanol in increasing concentration for 20 days. Following ethanol withdrawal, mice were administered distilled water (Group II), Dichrocephala integrifolia (25,50,100 and 200 mg/kg) (Groups III-VI) or diazepam (Group VII). Behavioural assessments were performed using the elevated plus maze, the open field and the hole board tests. Gamma-aminobutyric acid (GABA) concentration, GABA-Transaminase and glutamic acid decarboxylase activities were assessed in the brain. In the elevated plus maze, Dichrocephala integrifolia (100 mg/kg) significantly (p < 0.01) increased the percentage of open arms entries from 20.5 ± 1.56% in the negative control, to 65.3 ± 2.46%. In the hole board, the number of head dipping raised from 27.17 ± 0.60 in the negative control to 61.33 ± 2.82 (p < 0 0.01) at the dose 200 mg/kg of Dichrocephala integrifolia. Likewise, diazepam, Dichrocephala integrifolia (200 mg/kg) significantly (p < 0.01) raised GABA concentration from 267.70 ± 5.18 µg/g of tissue in the negative control to 395 ± 5.55 µg/g of tissue. The plant extract (200 mg/kg) reduced the activity of GABA-Transaminase from 101 ± 2.60 pg/min/mg of tissue in the negative control to 42.5 ± 2.35 pg/min/mg of tissue. From these results, we can conclude that, by enhancing the GABAergic neurotransmission, Dichrocephala integrifolia has anxiolytic activities against ethanol withdrawal anxiety and can therefore be a good drug candidate for the treatment of alcohol addiction.

Controlled atmosphere storage alleviates the browning of walnut (Juglans regia L.) fruit through enhancing GABA-mediated energy metabolism

Browning is the primary physiological damage that shortens the postharvest life and deteriorates the quality of stored fruits. Controlled atmosphere (CA) storage has been shown to be effective in alleviating the browning of ‘Xifu 1′ in-hull walnut; however, its alleviation mechanism is less understood. To further explore the effect and regulatory mechanism of CA on the browning of fresh in-hull walnut, we stored four varieties of in-hull walnuts under CA-treated (5% O2 + 7.5% CO2) and untreated conditions at 0 ± 0.5 °C with 70–80% relative humidity for 70 d. The indicators related to browning and γ-aminobutyric acid (GABA) metabolism were measured until 56 d of storage. The results showed that the CA significantly increased GABA levels by maintaining higher activities of glutamate decarboxylase (GAD), GABA transaminase (GABAT) and succinate dehydrogenase (SDH). This reduced the changes in the browning index (BI), color values, and respiration rate (RR) of the four walnut fruit varieties compared with controls during storage. Consistent with the active GABA metabolism, higher energy charge (EC) and adenosine triphosphate (ATP), succinic acid (SA), malic acid (MLA), fumaric acid (FA), and citric acid (CTA) contents were also observed in the CA-treated walnut hull compared to the controls. The epicarp degradation of the CA-treated ‘Xifu 1′ walnut fruit occurred later, and their mitochondria and cells maintained better integrity compared to the controls. Among the differentially expressed genes (DEGs) screened via RNA-Sequencing (RNA-Seq), 32 were annotated as part of the citrate cycle (TCA cycle) pathway, and 27 were annotated in the GABA metabolism pathway. Real-time quantitative PCR (RT-qPCR) analysis showed that eight candidate genes were closely related to the effect of CA on the synthesis, transport, and transformation of GABA. In conclusion, CA effectively controlled the browning of different varieties of fresh in-hull walnuts by enhancing GABA metabolism and maintaining energy balance.

Attenuation of Streptozotocin-Induced Diabetic Neuropathic Allodynia by Flavone Derivative Through Modulation of GABA-ergic Mechanisms and Endogenous Biomarkers.

Diabetic neuropathic pain is one of the most devasting disorders of peripheral nervous system. The loss of GABAergic inhibition is associated with the development of painful diabetic neuropathy. The current study evaluated the potential of 3-Hydroxy-2-methoxy-6-methyl flavone (3-OH-2'MeO6MF), to ameliorate peripheral neuropathic pain using an STZ-induced hyperglycemia rat model. The pain threshold was assessed by tail flick, cold, mechanical allodynia, and formalin test on days 0, 14, 21, and 28 after STZ administration accompanied by evaluation of several biochemical parameters. Administration of 3-OH-2'-MeO6MF (1,10, 30, and 100mg/kg, i.p) significantly enhanced the tail withdrawal threshold in tail-flick and tail cold allodynia tests. 3-OH-2'-MeO6MF also increased the paw withdrawal threshold in mechanical allodynia and decreased paw licking time in the formalin test. Additionally, 3-OH-2'-MeO6MF also attenuated the increase in concentrations of myeloperoxidase (MPO), thiobarbituric acid reactive substances (TBARS), nitrite, TNF-α, and IL 6 along with increases in glutathione (GSH). Pretreatment of pentylenetetrazole (PTZ) (40mg/kg, i.p.) abolished the antinociceptive effect of 3-OH-2'-MeO6MF in mechanical allodynia. Besides, the STZ-induced alterations in the GABA concentration and GABA transaminase activity attenuated by 3-OH-2'-MeO6MF treatment suggest GABAergic mechanisms. Molecular docking also authenticates the involvement of α2β2γ2L GABA-A receptors and GABA-T enzyme in the antinociceptive activities of 3-OH-2'-MeO6MF.

Effects of Phragmanthera capitata (Loranthaceae) on a model of anxiety-like behaviours induced by chronic immobilization stress in mice

This work aims to evaluate the anxiolytic-like effects of Phragmanthera capitata in a model of chronic immobilization stress in mice. Groups of mice were treated in ten consecutive days as follows: a normal control group (NaCl 0.9% per os), a negative control group (chronic immobilization stress + NaCl 0.9% per os), three test groups that were submitted to chronic immobilization stress (CIS) and received three doses of the plant (25, 125, and 250 mg/kg, p.o), and a positive control group (chronic immobilization stress + diazepam 2 mg/kg, i.p). Open field and dark/light tests were used for the evaluation of anxiolytic effects. Antioxidant activities and the involvement of gabaergic neurotransmission were determined by measuring the levels of malondialdehyde (MDA), reduced glutathione (GSH), catalase (CAT), gamma amino butyric acid (GABA), and GABA-transaminase (GABA-T) in the brain. Our results show that the highest dose of Phragmanthera capitata induced a significant increase (p &lt; 0.001) of time spent in the centre, number of crossing and number of grooming in the open field test and a significant increase (p &lt; 0.001) of time spent in the light compartment and the latency of the first escape in the light compartment of the dak/light test. The level of MDA and the activity of GABA-T were significantly decreased by the Phragmanthera capitata while reduced GSH, CAT and GABA, levels were increased. These results suggest that Phragmanthera capitata possesses anxiolytic-like effects that may be supported by its antioxidant activities and or the GABA neurotransmission.

CmCML11 interacts with CmCAMTA5 to enhance γ-aminobutyric acid (GABA) accumulation by regulating GABA shunt in fresh-cut cantaloupe

The effect of calcium chloride (CaCl2) treatment on γ-aminobutyric acid (GABA) accumulation in fresh-cut cantaloupe and the involved mechanisms were investigated. The result showed that 1% (w/v) CaCl2 treatment increased GABA content and activities of glutamate decarboxylase (GAD) and succinate semialdehyde dehydrogenase (SSADH), while decreased glutamate (Glu) content and GABA transaminase (GABA-T) activities in fresh-cut cantaloupe. CmCML11 and CmCAMTA5 expressions of CaCl2-treated fruit increased by 187.4% and 165.6% than control fruit in the initial 6 h. Besides, expressions of GABA shunt genes, including CmGAD1, CmGAD2, CmGABA-T and CmSSADH were also up-regulated by CaCl2 treatment during early storage. Moreover, acting as a transcriptional activator, CmCAMTA5 could bind to the CG-box in promoters of CmGAD1, CmGABA-T and CmSSADH and activate their transcription. Furthermore, the interaction between CmCML11 and CmCAMTA5 could enhance the transcriptional activation on GABA shunt genes which were regulated by CmCAMTA5. Collectively, our findings revealed that CaCl2 treatment promoted GABA accumulation in fresh-cut cantaloupe via the combined effect of CmCML11 and CmCAMTA5 in the regulation of expressions of CmGAD1, CmGABA-T, and CmSSADH in GABA shunt.

Contribution of Putrescine and Glutamic Acid on γ-Aminobutyric Acid Accumulation of Malus baccata Borkh. Roots under Suboptimal Low Root-Zone Temperature

GABA (γ-aminobutyric acid) is found in plants and accumulates rapidly under stresses. However, the contributions of glutamic acid and a (Glu)-derived pathway and polyamines (PAs) catabolism pathway on GABA accumulation and the regulatory effects of exogenous putrescine (Put) on a GABA shunt under suboptimal low root-zone temperatures remain unknown. Our results showed that suboptimal low root-zone temperatures (treatment L) significantly increased GABA contents and GABA transaminase (GABA-T) activities. The contribution rate of the PAs catabolism pathway increased from 20.60% to 43.31%. Treatment L induced oxidative stress in Malus baccata Borkh. roots. Exogenous Put increased the contents of endogenous Put, spermine (Spm), and spermidine (Spd), promoted the transformation of PAs, increased the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), and decreased the contents of hydrogen peroxide (H2O2), superoxide anion (O2∙−), and malondialdehyde (MDA). Meanwhile, contrasting results were observed after aminoguanidine (AG, an inhibitor of diamine oxidase) application. These findings revealed that the Glu-derived pathway is the main route of GABA synthesis. The contribution rate of the Pas catabolism pathway increased gradually with the extension of treatment time, and the treatment of exogenous Put significantly improved the tolerance of Malus baccata Borkh. Roots to suboptimal low temperature by regulating the transformation of Pas, GABA shunt, and the antioxidant system.

The Aqueous Lyophilisate of Alchemilla Kiwuensis Engl. (Rosaceae) Displays Antiepileptogenic and Antiepileptic Effects on PTZ-induced Kindling in rats: Evidence of Modulation of Glutamatergic and GABAergic Pathways Coupled to Antioxidant Properties.

Alchemilla kiwuensis Engl. (Rosaceae) (A. kiwuensis) is an herbaceous plant traditionally used by Cameroonians to treat epilepsy and other central nervous system disorders. The present study evaluated the antiepileptogenic and antiepileptic effects of A. kiwuensis (40mg/kg, 80mg/kg) following Pentylenetetrazole (PTZ)-induced kindling as well as its sub-chronic toxicity. Following an initial i.p administration of a challenge dose (70mg/kg), Wistar rats of both sexes received sub convulsive doses (35mg/kg) of PTZ every other day, one hour after the oral gavage of animals with treatments, until two consecutive stage 4, in all animals of negative control. Seizure progression, latency, duration, and repetition were noted. Twenty-four hours later, animals were dissected to extract their hippocampi. The resulting homogenates were used to evaluate Malondialdehyde, reduced glutathione, catalase activity, GABA, GABA-Transaminase, glutamate, glutamate transporter 2, IL-1β and TGF-1 β. Sub-chronic toxicity was conducted according to OECD 407 guidelines. The lyophilisate of A. kiwuensis significantly increased the latency of seizure appearance, delayed seizure progression and decreased seizure repetition and duration. Biochemical analysis revealed that the lyophilisate significantly increased the catalase activity, reduced glutathione, GABA, glutamate transporter 2 and TGF-1B levels. The lyophilisate equally caused a significant decreased in the GABA-Transaminase activity, malondialdehyde, and IL-1 β levels. There was no noticeable sign of toxicity. A. kiwuensis possesses antiepileptic and antiepiletogenic effects by enhancing GABAergic neurotransmission and antioxidant properties, coupled to modulation of glutamatergic and neuroinflammatory pathways and is innocuous in a sub-chronic model. These justifies its local use for the treatment of epilepsy.

Ameliorative Potential of (-) Pseudosemiglabrin in Mice with Pilocarpine-Induced Epilepsy: Antioxidant, Anti-Inflammatory, Anti-Apoptotic, and Neurotransmission Modulation

One prevalent neurological disorder is epilepsy. Modulating GABAergic/glutamatergic neurotransmission, Nrf2/HO-1, PI3K/Akt, and TLR-4/NF-B pathways might be a therapeutic strategy for epilepsy. Eight-week-old BALB/c mice were administered 12.5, 25, or 50 mg/kg (-) pseudosemiglabrin orally one hour before inducing epilepsy with an i.p. injection of 360 mg/kg pilocarpine. (-) Pseudosemiglabrin dose-dependently alleviated pilocarpine-induced epilepsy, as revealed by the complete repression of pilocarpine-induced convulsions and 100% survival rate in mice. Furthermore, (-) pseudosemiglabrin significantly enhanced mice’s locomotor activities, brain GABA, SLC1A2, GABARα1 levels, glutamate decarboxylase activity, and SLC1A2 and GABARα1mRNA expression while decreasing brain glutamate, SLC6A1, GRIN1 levels, GABA transaminase activity, and SLC6A1 and GRIN1 mRNA expression. These potentials can be due to the suppression of the TLR-4/NF-κB and the enhancement of the Nrf2/HO-1 and PI3K/Akt pathways, as demonstrated by the reduction in TLR-4, NF-κB, IL-1β, TNF-α mRNA expression, MDA, NO, caspase-3, Bax levels, and Bax/Bcl-2 ratio, and the enhancement of Nrf2, HO-1, PI3K, Akt mRNA expression, GSH, Bcl-2 levels, and SOD activity. Additionally, (-) pseudosemiglabrin abrogated the pilocarpine-induced histopathological changes. Interestingly, the (-) pseudosemiglabrin intervention showed a comparable effect to the standard medication, diazepam. Therefore, (-) pseudosemiglabrin can be a promising medication for the management of epilepsy.

Preparation of germinated brown rice with high γ-aminobutyric acid content and short root by magnetic field treatment

This study aimed to prepare germinated brown rice (GBR) with high γ-aminobutyric acid (GABA) content and short root length. Brown rice (BR) was exposed to 10 mT magnetic field at 25 °C for 60 min, followed by incubating in GABA solutions (0–10 mM, 30 °C) for 24 h. After treatment, GABA content in GBR significantly increased from 16.43 to 25.64–50.54 mg/100 g, while root length was shorter than 3.0 mm. Although GABA-aminotransferase activity was reduced by 4.61%–16.14%, the absorption of exogenous GABA caused by higher electrical conductivity, increased cell membrane permeability and more root hairs was the dominant reason for GABA accumulation. The hyperaccumulation of GABA conversely retarded the positive effect of M on α-amylase activity, starch structure, and anti-oxidase activity, thus maintaining the root length at 2.03–2.45 mm. Overall, this study provided an efficient method for preparing GBR with high GABA content and short root.

Metabolic Role of GABA in the Secretory Function of Pancreatic β-Cells: Its Hypothetical Implication in β-Cell Degradation in Type 2 Diabetes.

The stimulus-secretion coupling of a glucose-induced release is generally attributed to the metabolism of the hexose in the β-cells in the glycolytic pathway and the citric acid cycle. Glucose metabolism generates an increased cytosolic concentration of ATP and of the ATP/ADP ratio that closes the ATP-dependent K+-channel at the plasma membrane. The resultant depolarization of the β-cells opens voltage-dependent Ca2+-channels at the plasma membrane that triggers the exocytosis of insulin secretory granules. The secretory response is biphasic with a first and transient peak followed by a sustained phase. The first phase is reproduced by a depolarization of the β-cells with high extracellular KCl maintaining the KATP-channels open with diazoxide (triggering phase); the sustained phase (amplifying phase) depends on the participation of metabolic signals that remain to be determined. Our group has been investigating for several years the participation of the β-cell GABA metabolism in the stimulation of insulin secretion by three different secretagogues (glucose, a mixture of L-leucine plus L-glutamine, and some branched chain alpha-ketoacids, BCKAs). They stimulate a biphasic secretion of insulin accompanied by a strong suppression of the intracellular islet content of gamma-aminobutyric acid (GABA). As the islet GABA release simultaneously decreased, it was concluded that this resulted from an increased GABA shunt metabolism. The entrance of GABA into the shunt is catalyzed by GABA transaminase (GABAT) that transfers an amino group between GABA and alpha-ketoglutarate, resulting in succinic acid semialdehyde (SSA) and L-glutamate. SSA is oxidized to succinic acid that is further oxidized in the citric acid cycle. Inhibitors of GABAT (gamma-vinyl GABA, gabaculine) or glutamic acid decarboxylating activity (GAD), allylglycine, partially suppress the secretory response as well as GABA metabolism and islet ATP content and the ATP/ADP ratio. It is concluded that the GABA shunt metabolism contributes together with the own metabolism of metabolic secretagogues to increase islet mitochondrial oxidative phosphorylation. These experimental findings emphasize that the GABA shunt metabolism is a previously unrecognized anaplerotic mitochondrial pathway feeding the citric acid cycle with a β-cell endogenous substrate. It is therefore a postulated alternative to the proposed mitochondrial cataplerotic pathway(s) responsible for the amplification phase of insulin secretion. It is concluded the new postulated alternative suggests a possible new mechanism of β-cell degradation in type 2 (perhaps also in type 1) diabetes.

Exogenous γ-aminobutyric acid (GABA) improves salt-inhibited nitrogen metabolism and the anaplerotic reaction of the tricarboxylic acid cycle by regulating GABA-shunt metabolism in maize seedlings

Salinity stress hampers the growth of most crop plants and reduces yield considerably. In addition to its role in metabolism, γ-aminobutyric acid (GABA) plays a special role in the regulation of salinity stress tolerance in plants, though the underlying physiological mechanism remains poorly understood. In order to study the physiological mechanism of GABA pathway regulated carbon and nitrogen metabolism and tis relationship with salt resistance of maize seedlings, we supplemented seedlings with exogenous GABA under salt stress. In this study, we showed that supplementation with 0.5 mmol·L−1 (0.052 mg·g−1) GABA alleviated salt toxicity in maize seedling leaves, ameliorated salt-induced oxidative stress, and increased antioxidant enzyme activity. Applying exogenous GABA maintained chloroplast structure and relieved chlorophyll degradation, thus improving the photosynthetic performance of the leaves. Due to the improvement in photosynthesis, sugar accumulation also increased. Endogenous GABA content and GABA transaminase (GABA-T) and succinate semialdehyde dehydrogenase (SSADH) activity were increased, while glutamate decarboxylase (GAD) activity was decreased, via the exogenous application of GABA under salt stress. Meanwhile, nitrogen metabolism and the tricarboxylic acid (TCA) cycle were activated by the supply of GABA. In general, through the regulation of GABA-shunt metabolism, GABA activated enzymes related to nitrogen metabolism and replenished the key substrates of the TCA cycle, thereby improving the balance of carbon and nitrogen metabolism of maize and improving salt tolerance.

Exogenous γ-aminobutyric acid strengthens phenylpropanoid and nitrogen metabolism to enhance the contents of flavonoids, amino acids, and the derivatives in edamame.

γ-aminobutyric acid (GABA) has been reported to improve stress resistance in plants. Nonetheless, little is known about the effects of GABA on the nutritional quality and regulatory mechanisms of edamame. Therefore, we analyzed the flavonoid and amino acid (AA) metabolism and the effects of GABA on the nutrient content of edamame seeds through physiological and metabolomic analyses. Exogenous GABA increased endogenous GABA metabolism and GABA transaminase activity and enhanced the oxoglutarate content, which entered into nitrogen metabolism and increased the activity and expression of nitrogen metabolism-related enzymes, to accumulate AAs and bioactive peptides. Meanwhile, exogenous GABA induced the metabolism of flavonoids, including total flavonoids, anthocyanins, 6''-o-malonyglycitin, glycitin, ononin, cyanin, and ginkgetin, by increasing the activity and expression of flavonoid biosynthetic enzymes. This is the first study to reveal that GABA effectively improves the nutritional quality of edamame through the accumulation of AAs, bioactive peptides, isoflavones, anthocyanins, sugars, and organic acids.

Hydrogen Sulfide Mitigates Chilling Injury of Postharvest Banana Fruits by Regulating γ-Aminobutyric Acid Shunt Pathway and Ascorbate-Glutathione Cycle.

This study aimed to determine the effect of hydrogen sulfide on chilling injury (CI) of banana (Musa spp.) during cold storage (7°C). It was observed that hydrogen sulfide application (2 mmol L–1) markedly reduced the CI index and showed significantly higher chlorophyll contents, along with suppressed chlorophyll peroxidase and chlorophyllase enzyme activity. The treated banana fruits exhibited substantially higher peel lightness (L*), along with significantly a lower browning degree and soluble quinone content. The treated bananas had substantially a higher endogenous hydrogen sulfide content and higher activity of its biosynthesis-associated enzymes such as D-cysteine desulfhydrase (DCD) and L-cysteine desulfhydrase (LCD), along with significantly lower ion leakage, lipid peroxidation, hydrogen peroxide, and superoxide anion concentrations. Hydrogen sulfide-treated banana fruits showed an increased proline content and proline metabolism-associated enzymes including ornithine aminotransferase (OAT), Δ1-pyrroline-5-carboxylate synthetase (P5CS), and proline dehydrogenase (PDH). In the same way, hydrogen sulfide-fumigated banana fruits accumulated higher endogenous γ-aminobutyric acid (GABA) due to enhanced activity of glutamate decarboxylase (GAD) and GABA transaminase (GABA-T) enzymes. The hydrogen sulfide-treated fruits exhibited higher total phenolics owing to lower polyphenol oxidase (PPO) and peroxidase (POD) activity and stimulated phenylalanine ammonia lyase (PAL). The treated banana exhibited higher ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR), and superoxide dismutase (SOD) activity, along with higher glutathione (GSH) and ascorbic acid (AsA) concentrations and a significantly lower dehydroascorbic acid (DHA) content. In conclusion, hydrogen sulfide treatment could be utilized for CI alleviation of banana fruits during cold storage.

Postharvest γ-aminobutyric acid application mitigates chilling injury of aonla (Emblica officinalis Gaertn.) fruit during low temperature storage

Aonla is a nutrients rich underutilized subtropical fruit. It has short shelf life and is prone to chilling injury (CI) below 6 °C. So, the effect of γ-aminobutyric acid [5 mmol L−1 (GABA)] was investigated on aonla fruit CI mitigation during low temperature storage at 5 ± 1 °C for 24 d. Results showed that GABA treatment markedly suppressed CI, decay incidence, membrane permeability, malondialdehyde, superoxide anion and hydrogen peroxide in contrast with control. Treated fruit showed higher activity of glutamate decarboxylase (GAD) and GABA transaminase (GABA-T) enzymes which ultimately resulted in increased endogenous GABA content accumulation. Similarly, GABA application stimulated the activities of Δ1-pyrroline-5-carboxylate synthetase (P5CS) and ornithine aminotransferase (OAT) enzymes which thus enhanced proline accumulation. The GABA treated fruit exhibited higher phenylalanine ammonia lyase (PAL) and reduced polyphenol oxidase (PPO) enzyme activity and showed higher total phenols accumulation. In addition, total flavonoids, ascorbic acid and glutathione content were also significantly higher in GABA treated aonla fruit. In addition, GABA treated aonla fruit exhibited markedly higher ascorbate peroxidase (APX) catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) activities in comparison with the control. In addition, GABA treated fruit showed lower total soluble solids, ripening index and juice pH along with markedly higher concentration of titratable acidity. In conclusion, GABA treatment could be used for CI mitigation and overall quality maintenance of cold stored aonla fruit.

Melatonin treatment induces chilling tolerance by regulating the contents of polyamine, γ-aminobutyric acid, and proline in cucumber fruit

The mechanism of melatonin (MT) induced chilling tolerance in harvested cucumber fruit was investigated at commercial maturity. In this study, cucumber fruits were treated with 100 µmol L–1 MT at 4°C and 90% relative humidity for 15 d of storage. In comparison with the control, cucumber treatment with MT resulted in reduced chilling injury (CI), decreased electrolyte leakage and enhanced firmness. The fruits treated with MT showed higher chlorophyll contents in storage conditions with suppressed chlorophyllase enzyme activity. MT treatment increased arginine decarboxylase (ADC) and ornithine decarboxylase (ODC) enzyme activities. Moreover, enhanced expression of the Cucumis sativus ADC (CsADC) and C. sativus ODC (CsODC) genes resulted in the accumulation of polyamine contents. Similarly, proline levels exhibited higher levels among treated fruits. Meanwhile, the proline synthesizing enzymes △1-pyrroline-5-carboxylate syntheses (P5CS) and ornithine aminotransferase (OAT) were significantly increased, while a catabolic enzyme of proline dehydrogenase (PDH) activity was inhibited by treatment. In addition, MT induced expression of C. sativus OAT (CsOAT) and C. sativus P5CS (CsP5CS) genes. Cucumber fruits treated with MT also exhibited higher γ-aminobutyric acid (GABA) content by enhanced GABA transaminase (GABA-T) and glutamate decarboxylase (GAD) enzyme activities and a higher C. sativus GAD (CsGAD) gene expression. To sum up, the results show that MT treatment enhanced chilling tolerance, which was associated with the regulation of polyamines, as well as proline and γ-aminobutyric acid.