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The γ-aminobutyric acid (GABA) is a non-protein amino acid with some functional properties for human health. Its content is usually lower in plant seeds. Hypoxia or salt (NaCl) stress is an effective way for accumulating GABA during seed germination. However, NaCl stress on GABA accumulation under hypoxia is currently infrequent. The effect of NaCl on GABA accumulation in germinating faba bean (Vicia faba L.) under hypoxia was therefore investigated in this study. Faba bean seeds were steeped in citric acid buffer (pH 3.5) containing NaCl with a final O2 concentration of 5.5 mg L-1 and germinated for 5 d. Results showed that 60 mmol L-1 NaCl was the optimum concentration for GABA accumulation in germinating faba beans under hypoxia. Germination for 5 d under hypoxia-NaCl stress was less beneficial for GABA accumulation than only hypoxia (control). Polyamine degradation pathway played a more important role for accumulating GABA in germinating faba bean as an adaptive response to NaCl stress. Removing NaCl significantly increased GABA content, while it decreased glutamate decarboxylase (GAD) activity. Simultaneously, polyamine was accumulated, which might be related to the enhancement of physiological activity after recovery. When treated with aminoguanidine (AG) for 3 d, GABA content decreased by 29.82%. These results indicated that the tolerance ability of GABA shunt to NaCl stress was weaker than that of polyamine degradation pathway. The NaCl treatment for 3 d under hypoxia could raise the contribution ratio of polyamine degradation pathway for GABA accumulation. The contribution ratio of polyamine degradation pathway for GABA formation was 29.82% when treated for at least 3 d. [ABSTRACT FROM AUTHOR]

Effects of calcium on soybean growth and gamma-aminobutyric acid (GABA) accumulation pathways in germinating soybean were investigated. The harmful effect of NaCl stress was alleviated by CaCl while was aggravated by LaCl. Glutamate decarboxylase (GAD) activity increased significantly under NaCl plus CaCl treatment, while its gene expression levels had no significant changes compared with NaCl treatment. GAD and diamine oxidase (DAO) activities and their gene expression levels significantly decreased after LaCl was applied. When treated with AG, the soybean growth was suppressed and DAO activity was inhibited completely while DAO expression had no significant changes. Meanwhile, the GABA content decreased by 17.04 and 11.76 % in cotyledon and embryo under NaCl plus CaCl treatment compared with NaCl treatment, respectively. It can be concluded that CaCl addition changed the contribution ratio of GABA shunt and polyamine degradation pathway for GABA formation, and the increment of GABA in germinating soybean was mainly synthesized via GABA shunt. [ABSTRACT FROM AUTHOR]

Effects of NaCl stress and supplemental CaCl on soybean growth and gamma-aminobutyric acid (GABA) accumulation pathways in germinating soybean were investigated. Germinating under NaCl stress, GABA accumulation was caused not only by the activation of glutamate decarboxylase (GAD), diamine oxidase (DAO) and aminoaldehyde dehydrogenase (AMADH) existing in seed but also by their gene expression up-regulation during germination. However, after CaCl (6 mM) application, the harmful effect of NaCl stress (50 mM) was removed. GAD activity significantly increased, while its gene expression levels had no significant changes with the control, indicating that the increment in GAD activity was caused by the stimulation of exogenous Ca. Meanwhile, GABA was still accumulated although DAO and AMADH activities and their gene expression levels had no significant difference compared with the control. It can be concluded that CaCl addition decreased the contribution of polyamine degradation pathway to GABA accumulation compared with NaCl stress, and the increased GABA was mainly synthesized via GABA shunt. [ABSTRACT FROM AUTHOR]