Accumulation Of Gamma-aminobutyrate Research Articles

Accumulation of gamma-aminobutyrate (GABA) caused by heat-drying and expression of related genes in immature vegetable soybean (<i>edamame</i>)

We studied the effects of drying of immature seeds of vegetable soybean (Glycine max L. Merrill) on the accumulation of gamma-aminobutyrate (GABA) in the seeds. GABA accumulated after heat-drying, with the maximum at 40°C. The GABA content (447.5 mg/100 g DW) increased to more than 5 times the value in untreated seeds (79.6 mg/100 g DW). In contrast, the glutamate content decreased rapidly to 1/3 the level in the untreated seeds. The GABA content increased early in the heat-drying treatment: after 30 min, it had increased to 1.5 times the value in the untreated seeds. GABA did not accumulate in the vacuum-drying treatment. Among genes related to the GABA shunt, the gene for glutamate decarboxylase (EC 4.1.1.15), which catalyzes the decarboxylation of glutamate to produce GABA, showed relatively high expression, decreasing to only 70% of the value in untreated seeds even after 4 h of treatment. In contrast, expression of the genes for two catabolic mitochondrial enzymes, GABA transaminase (GABA-T; EC 2.6.1.19) and succinate semialdehyde dehydrogenase (SSADH; EC 1.2.1.16), decreased rapidly during heat-drying. These results suggest that the accumulated GABA was not metabolized rapidly by GABA-T and SSADH and therefore remained at high levels.

Amino acid pattern and glutamate metabolism during dehydration stress in the 'resurrection' plant Sporobolus stapfianus: a comparison between desiccation-sensitive and desiccation-tolerant leaves

The present study analyses changes in nitrogen compounds, amino acid composition, and glutamate metabolism in the resurrection plant Sporobolus stapfianus during dehydration stress. Results showed that older leaves (OL) were desiccation-sensitive whereas younger leaves (YL) were desiccation-tolerant. OL lost their soluble protein more rapidly, and to a larger extent than YL. Enzymes of primary nitrogen assimilation were affected by desiccation and the decrease in the glutamine synthetase (GS, EC 6.3.1.2) and ferredoxin-dependent GOGAT (Fd-GOGAT, EC 1.4.7.1) activities was higher in OL than in YL, thus suggesting higher sensibility to dehydration. Moreover, YL showed higher total GS enzyme activity at the end of the dehydration stress and was shown to maintain high chloroplastic GS protein content during the entire stress period. Free amino acid content increased in both YL and OL between 88% and 6% relative water content. Interestingly, OL and YL did not accumulate the same amino acids. OL accumulated large amounts of proline and gamma-aminobutyrate whereas YL preferentially accumulated asparagine and arginine. It is concluded (i) that modifications in the nitrogen and amino acid metabolism during dehydration stress were different depending on leaf development and (ii) that proline and gamma-aminobutyrate accumulation in S. stapfianus leaves were not essential for the acquisition of desiccation tolerance. On the contrary, the accumulation of large amounts of asparagine and arginine in the YL during dehydration could be important and serve as essential nitrogen and carbon reservoirs useful during rehydration. In this context, the role of GS for asparagine accumulation in YL is discussed.

Gamma-aminobutyrate: defense against invertebrate pests?

Gamma-aminobutyrate (GABA) is a ubiquitous four-carbon, non-protein amino acid. In plants, stress-induced GABA accumulation is well documented. However, the role(s) of GABA accumulation is contentious. In this Opinion article, we argue that wounding due to herbivory and crawling by insect larvae causes rapid GABA accumulation via the disruption of cellular compartmentation and the release of the acidic vacuolar contents to the cytosol. The activity of glutamate decarboxylase, the cytosolic enzyme responsible for GABA synthesis, has an acidic pH optimum. Subsequent GABA ingestion has a plant defense function by directly acting on GABA-regulated invertebrate neuromuscular junctions. Plants with an enhanced GABA-producing capacity reduce herbivory by invertebrate pests. These findings suggest that GABA accumulation is a rapidly deployed, local resistance mechanism that constitutes a first line of defense in deterring herbivory.

Gamma aminobutyrate: from intellectual curiosity to practical pest control

The authors describe the development of gamma aminobutyrate (GABA) as a potential control agent in plant – invertebrate pest systems. The evidence indicates that GABA accumulation in plants in response to biotic and abiotic stresses is mediated via the activation of glutamate decarboxylase. More applied research, based on the fact that GABA acts as an inhibitory neurotransmitter in invertebrate pests, indicates that ingested GABA disrupts nerve functioning and causes damage to oblique-banded leafroller larvae, and that walking or herbivory by tobacco budworm and oblique-banded leafroller larvae stimulate GABA accumulation in soybean and tobacco, respectively. In addition, elevated levels of endogenous GABA in genetically engineered tobacco deter feeding by tobacco budworm larvae and infestation by the northern root-knot nematode. It is concluded that genetically engineered crop species overexpressing glutamate decarboxylase and having high GABA-producing potential may be an alternative strategy to chemical pesticides for the management of invertebrate pests.Key words: gamma aminobutyrate, glutamate decarboxylase, invertebrate pests, plant defense.

Overexpression of glutamate decarboxylase in transgenic tobacco plants deters feeding by phytophagous insect larvae.

Gamma-aminobutyrate (GABA) is a ubiquitous four-carbon, non-protein amino acid synthesized by glutamate decarboxylase. Previous research suggests that the endogenous synthesis of GABA, a naturally occurring inhibitory neurotransmitter at neuromuscular junctions, serves as a plant resistance mechanism against invertebrate pests. In this study, two homozygous transgenic tobacco lines constitutively overexpressing a single copy of a full-length chimeric glutamate decarboxylase cDNA and possessing enhanced capacity for GABA accumulation (GAD plants), a homozygous transgenic line lacking the gene insert, and wild-type tobacco were employed. Tobacco budworm larvae were presented with plant attached wild type and transgenic leaves for 4 hr in a feeding preference study. Larvae consumed six to twelve times more leaf tissue from wild-type plants than from GAD plants. These results suggest that leaf GABA accumulation, which is known to occur in response to insect larval walking and feeding, represents a rapidly deployed local resistance mechanism.

Anaerobic Accumulation of γ-Aminobutyric Acid and Alanine in Radish Leaves (Raphanus sativus, L.)

In leaves, the anaerobic accumulation of alanine was accompanied by a loss of aspartate, and these changes preceded gamma-aminobutyrate accumulation and glutamate loss. Changes in keto acid content did not appear to be the cause of amino acid changes. Accumulation of gamma-aminobutyrate was due to acceleration of glutamate decarboxylation and arrest of gamma-aminobutyrate transamination. Changes in enzyme content did not explain the changes in reaction rates in vivo. Most of the aspartate may be converted anaerobically to alanine via oxalacetate and pyruvate.