[Effect of exogenous γ-aminobutyric acid on NO-N assimilation in muskmelon under Ca(NO) stress].

The effect of exogenous γ-aminobutyric acid (GABA) on NO-N assimilation in muskmelon under Ca(NO) stress was investigated in ' Yipintianxia 208', a salt-sensitive melon variety cultured under deep flow hydroponics which simulated soil salinization. The results showed that under Ca(NO) stress, the activities of nitrate reductase (NR), glutamate synthetase (GS) and glutamate amino transferase (GOGAT) in muskmelon seedlings were significantly reduced, while the activities of glutamate dehydrogenase (GDH), glutamate oxaloacetate transaminase (GOT) and glutamate pyruvate aminotransferase (GPT) were enhanced, leading to increased contents of NH-N and total amino acids, and decreased contents NO-N and soluble protein in muskmelon, which further severely inhibited plant growth and photosynthesis of muskmelon seedlings. Exogenous GABA effectively improved the absorption of NO-N in muskmelon roots and its transportation from root to shoot under Ca(NO) stress, and improved NH-N assimilation by enhancing NR, GS and GOGAT activities in muskmelon seedlings. Exogenous GABA also reduced NH release by limiting GDH deamination, thus further alleviated the toxication of NH-N induced by Ca(NO) stress. In addition, foliage spraying of GABA could regulate amino acids metabolic pathways and promote protein synthesis. The results suggested that exogenous GABA could improve NO-N assimilation and regulate amino acids metabolism to alleviate Ca(NO) stress damage in muskmelon seedlings.