Calcium regulating growth and GABA metabolism pathways in germinating soybean (Glycine max L.) under NaCl stress

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 CaCl2 while was aggravated by LaCl3. Glutamate decarboxylase (GAD) activity increased significantly under NaCl plus CaCl2 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 LaCl3 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 CaCl2 treatment compared with NaCl treatment, respectively. It can be concluded that CaCl2 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.