The use of deuterium-labeled gamma-aminobutyric (D(6)-GABA) to study uptake, translocation, and metabolism of exogenous GABA in plants

BACKGROUND: Exogenous 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. RESULTS: Herein, we used D(6)-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 D(6)-GABA could be easily distinguished from the non-labeled GABA after methyl chloroformate (MCF) derivatization. The D(6)-GABA was detected in the cortex (phloem), inner stem (xylem), and leaves after root drench. Girdling did not affect the translocation of D(6)-GABA, indicating that it is mainly translocated via the xylem. In addition, D(4)-labled succinic acid was detected in D(6)-GABA-treated plants, indicating that exogenous GABA was metabolized to succinic acid. The half-life of D(6)-GABA in citrus was about 1.3 h, indicating a quick conversion to succinic acid. CONCLUSION: The use of D(6)-GABA offers a valuable tool to study the translocation and metabolism of GABA in plants. D(6)-GABA and its metabolite (D(4)-succinic acid) can be easily distinguished from the endogenous GABA and succinic acid using GC–MS.