NaCl stress and supplemental CaCl2 regulating GABA metabolism pathways in germinating soybean

Effects of NaCl stress and supplemental CaCl2 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 CaCl2 (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 Ca2+. 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 CaCl2 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.