Our results showed that the activities of antioxidant enzymes increased under the mid-irrigation deficit in comparison to
full-irrigated condition. Although, the activities of antioxidant enzymes decreased when sunflower plants
suffered the extreme drought stress. The previous researches showed that enzymatic antioxidant systems, including CAT,
GPX, GR and SOD played an important role in scavenging harmful oxygen species (Larson, 1988; Burke and Mahan,
1991); and the activities of these antioxidant enzymes were altered when plants were subjected to stress. In full-irrigated
condition, the highest and lowest antioxidant enzymes content often were in Euroflor and Karaj hybrid, respectively.
However, often were in Euroflor and Karaj hybrid, respectively. However, the highest antioxidant enzymes
content were obtained from Allestar hybrid under water deficit conditions. The correlation results showed that there
was a high, positive and significant correlation among yield,CAT and GPX in mid-irrigation deficit. There was a high
relationship between GPX content and sunflower seed yield under full-irrigated and moderate water deficit conditions.
Thus, GPX content can be used as a drought tolerance index to selection tolerant Hybrids under moderate water deficit.
Moreover, the highest significant relationship between yield and antioxidant enzymes content was related to CAT in
extreme water deficit condition. Singh et al. (2010) found that a significant positive correlation of peroxidase with