Endogenous GABA levels decrease during grain maturation in wheat and do not play a role in the germination of immature grain

Abstract

It has been known that gamma-aminobutyric acid (GABA) is increased in germinating seeds such as those of wheat (Triticum aestivum L.). Techniques such as ninhydrin reaction method and high-performance liquid chromatography are used to quantify GABA levels. However, these methods require multiple steps and make it difficult to analyze multiple samples simultaneously. In this study, an enzyme-based assay for the rapid quantification of GABA levels in multiple wheat grain samples simultaneously was established. It was found that in developing grains, endogenous GABA levels were high but decreased with maturity. The maximum amount of GABA found in immature grains did not correlate with the degree of grain dormancy. However, the onset of decrease in GABA content was earlier in weak dormant lines compared to strong dormant lines. Endogenous GABA levels increased temporarily in strongly dormant grains upon imbibition, but quickly returned to their original levels, while they showed a sharp increase in intermediate dormant grains. Exogenous GABA promoted the germination of weakly dormant grains but was not sufficient to break dormancy in strongly dormant grains, suggesting that the maintenance of GABA levels may be related to the degree of grain dormancy.