This paper investigated the influence of
gamma-aminobutyric acid (
GABA) on
GABA metabolism and
amino acid content under
hypoxia stress by accurately controlling the level of dissolved
oxygen in hydroponics, using the roots of melon 'Xiyu 1' seedlings as the test material. The results showed that compared with the control, the growth of roots was inhibited seriously under
hypoxia stress. Meanwhile, the
hypoxia-treated roots had significantly higher activities of
glutamate decarboxylase (GAD),
glutamate dehydrogenase (GDH),
glutamate synthase (GOGAT),
glutamine synthetase (GS),
alanine aminotransferase (ALT),
aspartate aminotransferase (AST) as well as the contents of
GABA,
pyruvic acid,
alanine (Ala) and
aspartic acid (Asp). But the contents of
glutamic acid (Glu) and alpha-keto
glutaric acid in roots under
hypoxia stress was obviously lower than those of the control. Exogenous treatment with
GABA alleviated the inhibition effect of
hypoxia stress on root growth, which was accompanied by an increase in the contents of endogenous
GABA, Glu, alpha-keto
glutaric acid and Asp. Furthermore, under
hypoxia stress, the activities of GAD, GDH, GOGAT, GS, ALT, AST as well as the contents of
pyruvic acid and Ala significantly decreased in roots treated with
GABA. However, adding
GABA and viny-
gamma-aminobutyric acid (VGB) reduced the alleviation effect of
GABA on melon seedlings under
hypoxia stress. The results suggested that absorption of
GABA by roots could alleviate the injury of
hypoxia stress to melon seedlings. This meant that
GABA treatment allows the normal physiological metabolism under
hypoxia by inhibiting the GAD activity through feedback and maintaining higher Glu content as well as the bal- ance of
carbon and
nitrogen.