Amin Abbasi

This research was conducted to investigate the effect of different concentration of γ-_aminobutyric acid spraying on enzymatic antioxidant change on the defense system and lipid peroxidation of Thyme under water stress. This experiment was carried out as factorial experiment conducted based on a randomized complete block desing with three replication in the research greenhouse of the Department of Plant Production and Geneteics of Maraghe University. The main factor included levels of water stress (30%, 60%, 90% field capacity) and sub factors included no spraying of GABA. 25 mM GABA, 50 mM GABA and 75 mM GABA. According to the results the activity of Ascorbat peroxidas and Malondialdehid was effected by the intraction of water stress × foliar spraying. Also the results show that with increasing in stress intensity, the activity of Ascorbat peroxidas first increased and then whit increasing at the stress intensity, its activity was decreased. Also the highest level of Ascorbat peroxidas activity was obtained from the 25 mM GABA at 60 % FC. The amount of Malondialdehid was increased with increasing stress intensity. In addition, the lowest amount of malondialdehid was obtained from the 25 mM GABA at 90% FC. The use of GABA at 60 % FC compare to no spraying GABA caused by 73 % decrease in the amount of Malondialdehid.