Exogenous Application Of Gamma-aminobutyric Acid Research Articles

Integrating transcriptome and metabolome to explore the growth-promoting mechanisms of GABA in blueberry plantlets.

Tissue culture technology is the main method for the commercial propagation of blueberry plants, but blueberry plantlets grow slowly and have long growth cycles under in vitro propagation, resulting in low propagation efficiency. In addition, the long culturing time can also result in reduced nutrient content in the culture medium, and the accumulation of toxic and harmful substances that can lead to weak growth for the plantlets or browning and vitrification, which ultimately can seriously reduce the quality of the plantlets. Gamma-aminobutyric acid (GABA) is a four-carbon non-protein amino acid that can improve plant resistance to various stresses and promote plant growth, but the effects of its application and mechanism in tissue culture are still unclear. In this study, the effects of GABA on the growth of in vitro blueberry plantlets were analyzed following the treatment of the plantlets with GABA. In addition, the GABA-treated plantlets were also subjected to a comparative transcriptomic and metabolomic analysis. The exogenous application of GABA significantly promoted growth and improved the quality of the blueberry plantlets. In total, 2,626 differentially expressed genes (DEGs) and 377 differentially accumulated metabolites (DAMs) were detected by comparison of the control and GABA-treated plantlets. Most of the DEGs and DAMs were involved in carbohydrate metabolism and biosynthesis of secondary metabolites. The comprehensive analysis results indicated that GABA may promote the growth of blueberry plantlets by promoting carbon metabolism and nitrogen assimilation, as well as increasing the accumulation of secondary metabolites such as flavonoids, steroids and terpenes.

Exogenous Gamma-Aminobutyric Acid Application Induced Modulations in the Performance of Aromatic Rice Under Lead Toxicity.

Gamma-aminobutyric acid (GABA) is a non-protein amino acid and has a multi-functional role in abiotic stress tolerance. A pot experiment was conducted to assess the role of exogenous gamma-aminobutyric acid (GABA) application to modulate the growth, yield, and related physio-biochemical mechanisms in two aromatic rice cultivars, that is, Guixiangzhan (GXZ) and Nongxiang 18 (NX-18), under Pb toxic and normal conditions. The experimental treatments were comprised of Ck: without Pb and GABA (control), GABA: 1 mM GABA is applied under normal conditions (without Pb), Pb + GABA: 1 mM GABA is applied under Pb toxicity (800 mg kg−1 of soil), and Pb= only Pb (800 mg kg−1 of soil) is applied (no GABA). The required concentrations of GABA were applied as a foliar spray. Results revealed that Pb stress induced oxidative damage in terms of enhanced malondialdehyde (MDA), electrolyte leakage (EL), and H2O2 contents, while exogenous GABA application improved leaf chlorophyll, proline, protein and GABA contents, photosynthesis and gas exchange, and antioxidant defense under Pb toxicity in both rice cultivars. Moreover, glutamine synthetase (GS) and nitrate reductase (NR) activities were variably affected due to GABA application under Pb stress. The yield and related traits, that is, productive tillers/pot, grains/panicle, filled grain %, 1,000-grain weight, and grain yield were 13.64 and 10.29, 0.37% and 2.26%, 3.89 and 19.06%, 7.35 and 12.84%, and 17.92 and 40.56 lower under Pb treatment than Pb + GABA for GXZ and NX-18, respectively. Furthermore, exogenous GABA application in rice reduced Pb contents in shoot, leaves, panicle, and grains compared with Pb-exposed plants without GABA. Overall, GXZ performed better than NX-18 under Pb toxic conditions.

Exogenous Application of GABA Alleviates Alkali Damage in Alfalfa by Increasing the Activities of Antioxidant Enzymes

Alfalfa (Medicago sativa L.) is a widely grown and important forage crop. However, alkali stress is detrimental to alfalfa yield and nutritional quality. Gamma-aminobutyric acid (GABA) is a signaling molecule, it participates in and responds to metabolic regulation related to plant growth and development and stress. In this study, we clarify the effect of spraying alfalfa seedlings with GABA on the alkali tolerance of the seedlings. We determined that exogenous application of GABA at 75 mmol/L improved the resistance of alfalfa seedlings to alkali stress caused by exposure to 100 mmol/L NaHCO3, pH 8.5. Exogenous GABA significantly increased the chlorophyll content, the accumulation of soluble sugars in the plants, significantly decreased their relative electrical conductivity, malondialdehyde (MDA), superoxide anion (O2−) and hydrogen peroxide (H2O2) contents, and significantly increased the activities of the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD). Exogenous GABA increased the activities of GAD and GABA-T, increased the content of glutamate and endogenous GABA, and regulated the expression of the genes MsGAD, MsGABA-T and MsGDH. In alfalfa plants that survived for a long time, compared to the control group, root length and fresh weight were significantly higher. Exogenous GABA had a positive effect on the resistance of alfalfa seedlings to alkali stress, and the effect was closely associated with GAD and GABA-T activity, glutamate content and the levels of endogenous GABA and antioxidants. This work provides a new method for the cultivation of early-stage alfalfa seedlings under low or moderate alkali stress conditions through the application of 75 mmol/L GABA.

Characterization of GABA-Transaminase Gene from Mulberry (Morus multicaulis) and Its Role in Salt Stress Tolerance.

Gamma-aminobutyric acid (GABA) has been reported to accumulate in plants when subjected to salt stress, and GABA-transaminase (GABA-T) is the main GABA-degrading enzyme in the GABA shunt pathway. So far, the salt tolerance mechanism of the GABA-T gene behind the GABA metabolism remains unclear. In this study, the cDNA (designated MuGABA-T) of GABA-T gene was cloned from mulberry, and our data showed that MuGABA-T protein shares some conserved characteristics with its homologs from several plant species. MuGABA-T gene was constitutively expressed at different levels in mulberry tissues, and was induced substantially by NaCl, ABA and SA. In addition, our results demonstrated that exogenous application of GABA significantly reduced the salt damage index and increased plant resistance to NaCl stress. We further performed a functional analysis of MuGABA-T gene and demonstrated that the content of GABA was reduced in the transgenic MuGABA-T Arabidopsis plants, which accumulated more ROS and exhibited more sensitivity to salt stress than wild-type plants. However, exogenous application of GABA significantly increased the activities of antioxidant enzymes and alleviated the active oxygen-related injury of the transgenic plants under NaCl stress. Moreover, the MuGABA-T gene was overexpressed in the mulberry hairy roots, and similar results were obtained for sensitivity to salt stress in the transgenic mulberry plants. Our results suggest that the MuGABA-T gene plays a pivotal role in GABA catabolism and is responsible for a decrease in salt tolerance, and it may be involved in the ROS pathway in the response to salt stress. Taken together, the information provided here is helpful for further analysis of the function of GABA-T genes, and may promote mulberry resistance breeding in the future.

Host Gamma-Aminobutyric Acid Metabolic Pathway Is Involved in Resistance Against Rhizoctonia solani.

Rhizoctonia solani is a highly destructive necrotrophic fungal pathogen having a diverse host range, including rice and tomato. Previously R. solani infection has been found to cause large-scale readjustment in host primary metabolism and accumulation of various stress-associated metabolites such as gamma-aminobutyric acid (GABA) in rice. In this study, we report upregulation of GABA pathway genes during pathogenesis of R. solani in rice and tomato. The exogenous application of GABA provided partial resistance against R. solani infection in both the hosts. Furthermore, by using the virus-induced gene silencing approach, we knocked down the expression of some of the tomato genes involved in GABA biosynthesis (glutamate decarboxylase) and GABA catabolism (GABA-transaminase and succinic semialdehyde dehydrogenase) to study their role in host defense against R. solani infection. The silencing of each of these genes increased disease susceptibility in tomato. Overall the results from gene expression analysis, exogenous chemical application, and gene silencing studies suggest that the GABA pathway plays a positive role in plant defense against necrotrophic pathogen R. solani.

Assessing saffron response to salinity stress and alleviating potential of gamma amino butyric acid, salicylic acid and vermicompost extract on salt damage

Detailed information on response of saffron, one of the most economical medicinal plants, to high levels of saline (NaCl) water irrigation is not available. In this study, effect of spraying Gamma amino butyric acid (GABA), salicylic acid (SA) and vermicompost extract (VCE) on root structure, corm and flower production, K+ and Na+ allocation, physiological and photosynthesis aspects along with antioxidant enzymes activity of saffron were evaluated under saline water irrigation. The treatments consisted of adding four salinity doses to irrigation water (0, 5, 10 and 15 dS m−1 of NaCl) as main plot and four exogenous foliar applications (control, distilled water; GABA, 10 mM; SA, 1.5 mM and VCE, 5%) as subplot. The results illustrated that increasing root density; generating larger and heavier corms; and promoting Na+ exclusion and K+ accumulation were the main tolerance mechanisms which help saffron produce a satisfactory economical yield under salt stress conditions. All the foliar application treatments, especially VCE, could nullify the detrimental impacts of salinity. VCE remedied the nutrient deficiency caused by reducing soil osmotic potential and improved aerial K+/Na+ ratio in salinity conditions. Triggering antioxidant defense system was the most notable mechanism of GABA and SA that led to alleviation of adverse effect of salt stress. In conclusion, the results demonstrated that saffron can be introduced as a salt-tolerance crop and exogenous foliar application of VCE, GABA and SA are suggested for minimizing negative effects of salinity on saffron.

Gamma-aminobutyric acid (GABA) and acetylcholine (ACh) alleviate water deficit effects in soybean: From gene expression up to growth performance

Bioregulators act as priming agents under abiotic stress conditions. Bioregulators such as gamma-aminobutyric acid (GABA) and acetylcholine (ACh) affect the efficiency of the antioxidant system and the regulation of the stomatal aperture, respectively. The aim of this study was to verify a possible synergistic effect among these bioregulators as attenuators of the effects of water deficiency in Glycine max. We combined the application of GABA and ACh at 2.0 mM in soybean plants under different water regimes. The factors studied were: 1) application of Gaba and ACh in seeds (S); in leaves (L); in seeds and leaves (SL); control without application (C); and (2) water regimes at 100 % field capacity (FC) and water deficit (WD). When the application of bioregulators were removed from the process, a severe decrease in photosynthesis capacity (93 %) was observed on the sixth day (after withholding water), as well as a higher expression of the genes known to be induced by water deficit. The combination of GABA and ACh applied to seeds and leaves under water deficit resulted in a lower decline in photosynthesis, as well as better water-use efficiency and biomass production. Soybean plants subjected to this treatment also showed lower expression of GmABA2, GmLEA3 and GmP5CS genes, lower proline content and increased activity of SOD, CAT and APX compared to the control treatment. The results indicate that the combined exogenous application of GABA and ACh in soybean plants acted to promote increased tolerance to water deficit, showing their potential for use on agricultural areas which are prone to droughts.

Exogenous application of gamma-aminobutyric acid (GABA) alleviates the effect of water deficit stress in black cumin (Nigella sativa L.)

Water deficit is an abiotic stress factor that negatively affects black cumin (Nigella sativa L.) production. Gamma aminobutyric acid (GABA), an endogenous signaling molecule and metabolite, has high physiological and molecular activity in plant cells, which can promote tolerance to water deficit stress, but little information is available on the effect of exogenous application on growth of black cumin. A field experiment over two years was carried out at a farm located in Naqadeh-Urmia, West Azerbaijan, Iran to evaluate the effects of GABA on some agronomic and biochemical attributes of black cumin under water deficit stress conditions. Three irrigation treatments (irrigation after 50, 100, and 150 mm evaporation based on evaporation from class A pan) and four levels of GABA application (0, 0.5, 1.0, and 2.0 mg L−1) were tested. Irrespective of GABA application, the severe water deficit treatment (i.e., irrigation after 150 mm evaporation) provided the lowest seed number per follicle, 1000-seed weight, and seed yield. Increasing water deficit, significantly reduced chlorophyll a by 8.2 to 15.8% and chlorophyll b by 18.4 to 41.5%, whereas GABA application significantly improved these traits. The application of 2.0 mg L−1 GABA increased chlorophyll a content by 6.2% and chlorophyll b content by 19.2% compared with control. In addition, GABA application showed a positive and significant effect on soluble sugars content, proline accumulation, and catalase (CAT) activity. The maximum values of these variables were obtained with the application of GABA at 2.0 mg L−1. CAT, peroxidase (POX), and superoxide dismutase (SOD) activity increased with decreasing chlorophyll a and chlorophyll b contents, whereas soluble sugars and proline content increased with increasing activity of those antioxidant enzymes. Overall, in addition to cellular mechanisms, such as osmoregulation and antioxidant defense, GABA application can improve growth and productivity of black cumin under water deficit stress conditions.

Exogenous GABA application transiently improves the tolerance to root hypoxia on a sensitive genotype of Prunus rootstock

Prunus species are considered to be moderately sensitive to root hypoxia, but with some degree of tolerance to oxygen deficiency. In a previous work on a set of commercial Prunus rootstocks we identified the plum-based rootstock ‘Mariana 2624’ and the cherry-based rootstock ‘Mazzard F12/1’ as the most tolerant and sensitive genotypes, respectively, to root hypoxia by waterlogging. We then sequenced, for both genotypes, the root transcriptome responsive to hypoxic conditions. The early differentially expressed genes included a transcript with high homology to a root-specific Glutamate decarboxylase of Arabidopsis, AtGAD1. A homology search of the peach genome detected four putative GAD sequences. They exhibited a very high identity in their deduced amino acid sequences except in the C-terminal region, where the calmodulin binding domain is located. In addition, these GAD isoforms showed organ-specific expression and different transcriptional responses to root hypoxia stress. GAD is the enzyme responsible for the synthesis of gamma aminobutyric acid (GABA), an amino acid that reaches high levels during stresses. We assessed the effect of exogenous GABA application on molecular, physiological, biochemical and metabolic parameters in ‘Mariana 2624’ and ‘Mazzard F12/1’. The root hypoxia-tolerant genotype was unaffected by GABA supplementation. In contrast, exogenous GABA triggered transient but substantive changes in the root hypoxia-sensitive genotype under waterlogging. This effect was associated with changes in the mRNA levels of some GAD isoforms, an improvement in photosynthetic parameters, a higher CO2 assimilation rate and stomatal conductance, a smaller loss of chlorophyll content, lower levels of H2O2 and increased levels of endogenous GABA. We discuss GABA’s wide spectrum of biological actions and its effect on root hypoxia-sensitive Prunus species’ adaptive response to oxygen deficiency.

Gamma-aminobutyric acid mediates nicotine biosynthesis in tobacco under flooding stress

Gamma-aminobutyric acid (GABA) is a four-carbon non-protein amino acid conserved from bacteria to plants and vertebrates. Increasing evidence supports a regulatory role for GABA in plant development and the plant's response to environmental stress. The biosynthesis of nicotine, the main economically important metabolite in tobacco, is tightly regulated. GABA has not hitherto been reported to function in nicotine biosynthesis. Here we report that water flooding treatment (hypoxia) markedly induced the accumulation of GABA and stimulated nicotine biosynthesis. Suppressing GABA accumulation by treatment with glutamate decarboxylase inhibitor impaired flooding-induced nicotine biosynthesis, while exogenous GABA application directly induced nicotine biosynthesis. Based on these results, we propose that GABA triggers nicotine biosynthesis in tobacco seedlings subjected to flooding. Our results provide insight into the molecular mechanism of nicotine biosynthesis in tobacco plants exposed to environmental stress.

Pyramidal cell responses to γ‐aminobutyric acid differ in type I and type II cortical dysplasia

Abnormalities in the gamma-aminobutyric acid (GABA)-ergic system could be responsible for seizures in cortical dysplasia (CD). We examined responses of pyramidal neurons to exogenous application of GABA, as well as alterations of GABAergic interneuron number and size in pediatric epilepsy surgery patients with non-CD, type I CD, and type II CD pathologies. We used the dissociated cell preparation for electrophysiology along with immunohistochemistry to identify number and size of GABAergic cells. Pyramidal neurons from type I CD tissue showed increased EC(50) and faster kinetics compared with cells from non-CD and type II CD tissue. Cytomegalic pyramidal neurons showed increased GABA peak currents and decreased peak current densities, longer kinetics, and decreased sensitivity to zolpidem and zinc compared with normal pyramidal cells from non-CD and type I CD. There were fewer but larger glutamic acid decarboxylase (GAD)-containing cells in type II CD tissue with cytomegalic neurons compared with non-CD, type I CD, and type II CD without cytomegalic neurons. In addition, GABA transporters (VGAT and GAT-1) showed increased staining surrounding cytomegalic neurons in type II CD tissue. These results indicate that there are differences in GABA(A) receptor-mediated pyramidal cell responses in type I and type II CD. Alterations in zolpidem and zinc sensitivities also suggest that cytomegalic neurons have altered GABA(A) receptor subunit composition. These findings support the hypothesis that patients with type I and type II CD will respond differently to GABA-mediated antiepileptic drugs and that cytomegalic neurons have features similar to immature neurons with prolonged GABA(A) receptor open channel times.

Immature Neurons and GABA Networks May Contribute to Epileptogenesis in Pediatric Cortical Dysplasia

Cortical dysplasia (CD), a frequent pathological substrate of pediatric epilepsy surgery patients, has a number of similarities with immature cortex, such as reduced Mg2+ sensitivity of N-methyl-D-aspartate (NMDA) receptors and the persistence of subplate-like neurons and undifferentiated cells. Because gamma-aminobutyric acid (GABA) is the main neurotransmitter in early cortical development, we hypothesized increased GABA receptor-mediated synaptic function in CD tissue. Infrared videomicroscopy and whole-cell patch clamp recordings were used to characterize the morphology and electrophysiological properties of immature and normal-appearing neurons in slices from cortical tissue samples resected for the treatment of pharmacoresistant epilepsy in children (0.2-14 years). In addition, we examined spontaneous and evoked synaptic activity, as well as responses to exogenous GABA application. We demonstrate both the presence of immature pyramidal neurons and networks in young CD tissue and the predominance of GABA synaptic activity. In addition, spontaneous GABA depolarizations frequently induced action potentials, supporting a potential excitatory role of GABA in CD. Evoked synaptic responses mediated by GABA were also prominent, and bath application of 4-aminopyridine induced rhythmic depolarizations that were blocked by bicuculline. Finally, responses to exogenous application of GABA had depolarized reversal potentials in severe compared to mild and non-CD cases. The present data support the hypothesis that CD shares features of immature cortex, with predominant and potentially excitatory GABA(A) receptor-mediated neurotransmission. These results could partially explain the increased excitability of the cortical network in pediatric CD.

Suppression of sustained and transient ON signals of amacrine cells by GABA is mediated by different receptor subtypes

Intracellular recordings were made from amacrine cells in the isolated, superfused carp retina, and the effects of gamma-aminobutyric acid (GABA) on sustained and transient ON signals of these cells were studied. Exogenous GABA application partially suppressed the sustained response of ON amacrine cells, which could be completely reversed by picrotoxin (PTX), a chloride channel blocker, and by bicuculline (BCC), a specific GABA(A) receptor antagonist. On the other hand, suppression by GABA of the ON response which was predominantly driven by rod signals in a certain portion of transient ON-OFF amacrine cells was completely blocked by PTX, but not by BCC, indicating that GABA(C) recepton may be involved in the effect. These results suggest that GABA(A), and GABA(C) receptors may be respectively involved in mediating the transmission of sustained and transient signals in the carp inner retina.