Amin Abbasi

The purpose of this study is to investigate the effect of spraying different concentrations of gamma-aminobutyric acid on the thyme defense system and improving water deficit 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, Maraghe University. The main factor included levels of deficit irrigation (30%, 60%, 90% field capacity) and sub factors included no spraying of GABA. 25 mM GABA, 50 mM GABA and 75 mM GABA. The results obtained from this research showed that the effect of intraction of water stress × GABA spraying on the activity level of guaiacol peroxidase enzyme as well as carotenoid content was significant. Also, the results of mean comparison showed that with the increasing stress intensity, the activity of this enzyme first increased and then its activity decreased at the high stress intensity. The highest level of guaiacol peroxidase enzyme activity is related to the treatment of 25 mM GABA at 60 % FC. Carotenoid content also increased with increasing stress intensity. In addition, the highest and lowest levels of carotenoid content were obtained from the treatment of 25 mM GABA at 90% FC and the absence of GABA at 30% FC.