The study was carried out in plant tissue culture laboratory, University of Baghdad during the period 2017-2019, as factorial experiment in complete randomized design, to study the effect of PEG at (0, 2, 4, 6 and 8%) on physiological and chemical changes in callus of three sunflower (Ishaqi 1, Aqmar and Al-haga) induced by the cultivation of the young stem in vitro under water stress. The content of callus cells of SOD, POD, CAT and APX enzymes as well as content of hydrogen peroxide were determined as indicators to determine the effect of PEG in callus tissue cells cultivated on medium equipped with the PEG concentrations. The results showed that cultivars were differs significantly and Al-hajavariety was superior in increasing SOD to 24.43 absorption unit mg-1 protein, and the variety Aqmar was superior in increasing POD, CAT and APX to 20.38, 4.30 and 0.1486 absorption unit mg-1 protein respectively. Ishaqi1 variety was superior in increasing hydrogen peroxide content to 37.536 Mmol g-1. PEG concentrations significantly affected enzyme activity and 6% gave the highest efficacy of SOD, POD and CAT reached to 24.06, 13.36 and 4.00 absorption unit mg-1 protein respectively, while 4% PEG gave the highest effective of APX reached to 0.1378 absorption unit mg-1 protein. Hydrogen peroxide content achieved the highest mean at 0% PEG and reached to 37.536 Mmol.g-1. The interaction caused significant effect and the highest SOD enzyme was obtained from Al-haja variety at 6% PEG, while POD, CAT and APX enzymes (28.16, 7.25 and 0.2375 unit absorption mg-1 protein) were obtained with Aqmar variety at the concentrations of 6, 6 and 4% PEG, respectively. Ishaqi 1 variety at 0% PEG gave the highest average of Hydrogen peroxide content reached to 38.260 mg g-1. It was appeared that (by using plant tissue culture technique). Aqmar was superior in increasing the effectiveness of POD, CAT and APX enzymes compared to other two varieties, which was important indicator to increase plant water stress tolerance.
