Abstract:

In the present study, the effect of CaCl2 and ethylene glycol tetraacetic acid (EGTA) on the main physiological
indicators and gamma-aminobutyric acid (GABA) accumulation in germinating soybean under NaCl stress was investigated.
Compared with NaCl stress alone, the sprout length and respiratory rate increased significantly under NaCl stress combined
with CaCl2 treatment, indicating that exogenous CaCl2 mitigated the negative effect of NaCl stress. Meanwhile, CaCl2 led
to a significant increase in catalase (CAT) and peroxidase (POD) activities and could therefore alleviate the harmful effect
of NaCl stress on the growth of germinating soybean. In contrast, the above effects were reversed by combination with
EGTA. Under the supplemental CaCl2 treatment, there was no significant difference in GABA content in the cotyledon and
embryo of germinating soybean compared with NaCl stress treatment alone but it was significantly higher than the control.
Furthermore, when aminoguanidine (AG), an amine oxidase inhibitor, was added under NaCl plus CaCl2 treatment, GABA
content in the cotyledon and embryo was decreased by 17.1% and 26.5%, respectively. In addition, AG added under NaCl
combined with EGTA treatment resulted in a decrease in GABA content in cotyledon and embryo by 9.8% and 8.5%,
respectively. The present study indicates that exogenous calcium countered the harmful effect of salt stress and increased
the biomass and GABA content of germinating soybeans. Moreover, CaCl2 or EGTA addition decreased the contribution of
polyamine degradation pathway to GABA accumulation compared to NaCl stress.

Key words: soybean, germination, gamma-aminobutyric acid, NaCl stress