Abstract
BackgroundExogenous application of gamma-aminobutyric acid (GABA) could relieve stress symptoms caused by abiotic stresses including anoxia, heat and cold shock, drought, and salt. However, studying translocation and metabolism of exogenous GABA is challenged by the presence of endogenous GABA.ResultsHerein, we used D6-GABA in order to investigate the uptake, translocation, and the metabolism of exogenous GABA in Mexican lime (Citrus aurantifolia) seedlings using gas chromatography-mass spectrometry (GC–MS). The GC–MS analysis showed that D6-GABA could be easily distinguished from the non-labeled GABA after methyl chloroformate (MCF) derivatization. The D6-GABA was detected in the cortex (phloem), inner stem (xylem), and leaves after root drench. Girdling did not affect the translocation of D6-GABA, indicating that it is mainly translocated via the xylem. In addition, D4-labled succinic acid was detected in D6-GABA-treated plants, indicating that exogenous GABA was metabolized to succinic acid. The half-life of D6-GABA in citrus was about 1.3 h, indicating a quick conversion to succinic acid.ConclusionThe use of D6-GABA offers a valuable tool to study the translocation and metabolism of GABA in plants. D6-GABA and its metabolite (D4-succinic acid) can be easily distinguished from the endogenous GABA and succinic acid using GC–MS.
Highlights
MethodsPlant materials Mexican lime (Citrus aurantifolia) was used in this study
Exogenous application of gamma-aminobutyric acid (GABA) could relieve stress symptoms caused by abiotic stresses including anoxia, heat and cold shock, drought, and salt
The gas chromatography-mass spectrometry (GC–MS) and the gene expression results together showed that exogenous GABA was metabolized to succinic acid (Fig. 4c)
Summary
Plant materials Mexican lime (Citrus aurantifolia) was used in this study. Seeds were potted in plastic cones (20 × 4 cm) containing Sungro professional growing mix (Sungro Horticulture, Agawam, MA). Seedlings were kept in a greenhouse (28 ± 1 °C, 60 ± 5% relative humidity, L16:D8 h photoperiod) at the Citrus Research and Education Center (CREC), University of Florida, Lake Alfred, Florida. At the time of experiment, plants were about three-month old and around 15 ± 5 cm tall. Preparation of GABA standards D6-GABA and GABA standards were purchased from Sigma Aldrich (St. Louis, MO). Stock solutions of GABA (10 mM), D6-GABA (10 mM), and succinic acid (10 mM) were prepared daily using distilled water. A set of serial dilutions were made and used to construct the standard curves
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