BACKGROUND: γ-Aminobutyric acid (GABA) can be synthesised by the GABA shunt and polyamine degradation pathway in plants under hypoxia stress and lower temperature. The hypoxia germination freeze-thawing incubation was used as a new technique for accumulating more GABA in soybean. RESULTS: Results showed that glutamate decarboxylase (GAD) and diamine oxidase (DAO) activity as well as GABA content increased during germination within 24 h under hypoxia. However, the contents of dry matters and protein decreased. When the hypoxia-treated sprouts were frozen at -18 °C for 12 h and thawed at 25 °C for 6 h, GABA content increased drastically to 7.21-fold of the non-frozen sprouts. Subsequently, the freeze-thawing sprouts were ground into homogenates and incubated. GABA content was 14.20-fold of the only-soaked seeds when homogenates was incubated at 45 °C for 80 min within 400 µmol L(-1) pyridoxine (VB6) (pH 6.5). CONCLUSION: The hypoxia germination freeze-thawing incubation was an effective method for accumulating GABA in soybean. During incubation, DAO was more important for GABA formation in homogenate of germinated soybean compared with GAD.
BACKGROUND: γ-Aminobutyric acid (GABA) can be synthesised by the GABA shunt and polyamine degradation pathway in plants under hypoxia stress and lower temperature. The hypoxia germination freeze-thawing incubation was used as a new technique for accumulating more GABA in soybean. RESULTS: Results showed that glutamate decarboxylase (GAD) and diamine oxidase (DAO) activity as well as GABA content increased during germination within 24 h under hypoxia. However, the contents of dry matters and protein decreased. When the hypoxia-treated sprouts were frozen at -18 °C for 12 h and thawed at 25 °C for 6 h, GABA content increased drastically to 7.21-fold of the non-frozen sprouts. Subsequently, the freeze-thawing sprouts were ground into homogenates and incubated. GABA content was 14.20-fold of the only-soaked seeds when homogenates was incubated at 45 °C for 80 min within 400 µmol L(-1) pyridoxine (VB6) (pH 6.5). CONCLUSION: The hypoxia germination freeze-thawing incubation was an effective method for accumulating GABA in soybean. During incubation, DAO was more important for GABA formation in homogenate of germinated soybean compared with GAD.