Under drought stress conditions, increase of the active oxygen specieses causes damage to the major cell macromolcules such as lipids, proteins and carbohydrates. Some enzymatic systems have a critical role in scavenging cells from these active oxygen species. Changes of catalase and peroxidase activities and their effects on chlorophyll and membrance stability were investigated in tolerant (Azadi, Roshan and M-79-4), Semi-tolerant (M-79-17 and Karaj 1) and succeptible (Kavir and Marvdasht) wheat cultivars. Peroxidase activiy increased in Azadi, M-79-4 and M-79-17 under drought stress. Although, peroxidase activity didn’t increased in Roshan, this cutlivar showed the highest level of this enzyme activity under both drought and control conditions. The activity of catalase remained constant or decreased in all cultivars under drought stress, and there wasn’t a clear relationship between catalase activity and drought tolerance. Azadi, Roshan, M-79-4 and Karaj 1 showed the highest chlorophyll stability index. Also, M-79-17 and Roshan showed the highest while Kavir showed the lowest cell membrane stability under drought stress. Under drought stress condition there was a positive correlations between peroxidase activity and yield and chlorophyll b stability index but, catalase activity didn’t show positive correlation with yield. Also, there was a negative correlation between peroxidase activity and cell membrane injury during drought stress. Our results suggested that peroxidase activity under drought stress resulted in cell membrane and chlorophyll stability and is closely associated with cultivars’ tolerance to drought stress.
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