Effects of ABA and CaCl₂ on GABA accumulation in fava bean germinating under hypoxia-NaCl stress

<div><p>Effects of exogenous abscisic acid (ABA) and CaCl₂ on γ-aminobutyric acid (GABA) accumulation of germinated fava bean under hypoxia-NaCl stress were investigated. Exogenous ABA resulted in the enhancement of glutamate decarboxylase (GAD) and diamine oxidase (DAO) activity as well as GABA content in cotyledon and shoot. CaCl₂ increased both enzyme activities in shoot and GABA content in cotyledon and shoot. ABA downregulated <i>GAD</i> expression in cotyledon and radicle, while upregulated that in shoot; it also upregulated <i>DAO</i> expression in each organ. CaCl₂ upregulated <i>GAD</i> expression in cotyledon, while downregulated that in radicle. However, it upregulated <i>DAO</i> expression in shoot, downregulated that in radicle. ABA inhibitor fluridon and ethylenediaminetetraacetic acid inhibited GAD and DAO activities significantly so that inhibited GABA accumulation through reducing ABA biosynthesis and chelating Ca²⁺, respectively. However, they upregulated <i>GAD</i> and <i>DAO</i> expression in varying degrees. These results indicate that ABA and Ca²⁺ participate in GABA biosynthesis in fava bean during germination under hypoxia-NaCl stress.</p>