International Science Community Association Research Journal of Recent Sciences 2277 - 2502 1 6 2012 June 2 Improving Barley Yield Grown Under Water Stress Conditions 1 6 EN Mostafa M.Rady 1 Agricultural Botany Department, Faculty of Agriculture, Fayoum University, 63514-Fayoum, EGYPT Water Relations and Field Irrigation Dept. National Research Centre, Cairo, 12622 EGYPT MaybelleS. Gaballah 2 > Research Paper 2012 4 30 2012 June 2 A field experiment was conducted to investigate the influences of paclobutrazol (PBZ) on leaf water potential (), proline content, activities of antioxidant enzymes like superoxide dismutase (SOD) and catalase (CAT), grain yield and water use efficiency (WUE) of barley ‘cv. Giza 124’ plants subjected to water stress. Plants were treated with two regimes of irrigation water, i.e., 100% of evapotranspiration (ETc) (control) and 60% of ETc and three levels of PBZ solution (0.0 (control), 20 and 40 mg l-1). Leaf water potential, proline content, activities of SOD and CAT, grain yield and WUE were signicantly altered by both water stress and PBZ treatments. Results indicated that PBZ (40 mg l-1) mitigated the water stress and significantly reduced the reduction in leaf as compared to non-PBZ-treated water-stressed plants. Water-stressed plants treated with PBZ (40 mg l-1) had significant higher proline content than water-stressed plants without PBZ treatment. Higher antioxidant enzyme activity was also observed in water-stressed plants treated by PBZ than water-stressed plants without PBZ treatments. In comparison to water-stressed plants without PBZ treatment, water-stressed plants treated with PBZ (40 mg l-1) had significant higher SOD and CAT activities. Furthermore, water-stressed plants treated with 40 mg l-1 ofPBZ had also significant higher grain yield and WUE as compared to water-stressed plants without PBZ treatment. The results suggest that PBZ application under water stress conditions alters the equilibrium between free radical production and enzymatic defense reactions in barley by enhancing the proline content and free radical scavenging capacity. Copyright@ International Science Community Association