Abstract:

To explore the effect of γ-aminobutyric acid（GABA）on the growth，substance content
related to nitrate metabolism，key enzyme activities as well as gene and protein expression in pak-choi
（Brassica campestris ssp. chinensis Makino），the plants grown in nutrient solution with high nitrate
nitrogen were used as sample materials after the seeds were soaked with GABA at the concentration of 5
and 10 mmol · L-1. The results showed that compared with the control and nitrate application treatments，GABA soaking significantly improved the growth of the pak-choi，increased the activities of nitrate
reductase（NR）and nitrite reductase（NiR），glutamic acid decarboxylase（GAD），and gene and protein
expression in leaves. As a result，GABA soaking treatment decreased the contents of nitrate and nitrite
nitrogen in leaves，but the contents of ammomium nitrogen（NH4-N），glutamate（Glu）and endogenous
GABA maintained at a higher level. Further analysis showed that the effect of GABA soaking on nitrogen
metabolism varied with treatment time and concentration. It showed the better result at 0-12 days after
high nitrate application，and the GABA soaking effect at concentration of 5 mmol · L-1；meanwhile，GABA
influenced the key enzyme gene and protein expression was earlier than that of enzyme activities. The
results indicated that GABA soaking treatment promoted plant growth as well as the metabolism of nitrate
reduction and assimilation through the increase of NR and GAD activities，gene and protein expression，
and consequently，reduced nitrate content in leaves，improved yield and quality of pak-choi.

Key words: pak-choi, GABA, high nitrogen treatment, nitrate metabolism, gene expression, protein
expression