The Production and Efflux of 4-Aminobutyrate in Isolated Mesophyll Cells

Abstract

The pathway of 4-aminobutyric acid (GABA) production and efflux was investigated in suspensions of mesophyll cells isolated from asparagus (Asparagus sprengeri Regel) cladophylls. Analysis of free amino acids demonstrated that, on a molar basis, GABA represented 11.4, 19, and 6.5% of the xylem sap, intact cladophyll tissue, and isolated mesophyll cells, respectively. LGlu, a GABA precursor, was abundant in intact cladophylls and isolated cells but not in xylem sap. When cells were incubated with L-[U-14C]Glu, intracellular GABA contained less than 10% of the radioactivity found in intracellular Glu. However, GABA in the medium contained 78% of the radioactivity found in extracellular L-Glu metabolites. Incubation with L-[1-14C]Glu resulted in the appearance of unlabeled GABA, demonstrating its production through decarboxylation at carbon 1. GABA released to the medium from cells incubated with L-[U-14C]Glu had a specific activity of 18 nanocuries per nanomole, whereas GABA remaining in the cell had a specific activity of 2.25 x 10-' nanocuries per nanomole. In the presence of exogenous L-Glu, amino acid analysis and cell volume measurements indicated intracellular Ala and GABA concentrations of 4.2 and 1.4 millimolar, respectively. In the medium, however, the corresponding concentrations were 2 and 57 micromolar. The data indicate that L-GIu entering the cell is decarboxylated to GABA, and that specific and passive efflux is from this pool of recently synthesized GABA and not from a previously synthesized unlabeled pool of GABA.shown that GABA efflux is slower than that for other amino acids, suggesting that it is sequestered in an organelle (19).

High quality reference genome of drumstick tree (Moringa oleifera Lam.), a potential perennial crop

“…hypoxia, temperature shock, mechanical manipulation and damage, water stress and phytohormones [70,71]. Here, we found that GABA is synthesized almost exclusively by the irreversible α-decarboxylation of L-glutamate by glutamate decarboxylase (GAD; annotated gene: lamu_GLEAN_10006873, lamu_GLEAN_ 10006874, lamu_GLEAN_10004957, lamu_GLEAN_ 10007711, lamu_GLEAN_10007712, lamu_GLEAN_ 10007713) [72,73]. Subsequently, GABA is catabolized by GABA transaminase (GABA-T; annotated gene: lamu_ GLEAN_10002543) and succinate semialdehyde dehydrogenase (SSADH; annotated gene: lamu_GLEAN_10008793, lamu_GLEAN_10008794) to succinate, an important Kerbs cycle metabolite [73].…”

Evidence that γ-aminobutyric acid is a major nitrogen source during Cladosporium fulvum infection of tomato

“…This raises questions regarding the role of the GABA shunt in fungi and indeed other systems. While the expression of ugatA in U. maydis was not investigated when grown in glutamate, it has been suggested that in isolated asparagus mesophyll cells elevated glutamate levels stimulate GABA synthesis (Chung et al 1992;Cholewa et al 1997). Very little is known in fungi about GAD and even less about its regulation.…”

[beta]-Aminobutyric Acid Induces the Accumulation of Pathogenesis-Related Proteins in Tomato (Lycopersicon esculentum L.) Plants and Resistance to Late Blight Infection Caused by Phytophthora infestans

“…Although some are biologically toxic, they can also serve as a nitrogen source (Rosenthal, 1982). GABA appears to be ubiquitous in the plant kingdom (Chung et al, 1992), but the physiological role of GABA in plants has not been clearly established. GABA synthesis results predominantly from the decarboxylation of carbon-1 of t-glutamate in a reaction catalyzed by glutamate decarboxylase (Satya Narayan and Nair, 1990).…”