responses of photosynthesis, cell membrane stability and antioxidative enzymes to drought stress and nitrogen fertilizer in two barley (hordeum vulgare) cultivars under controlled condition

in order to investigate the effects of drought stress and nitrogen fertilizer on photosynthesis rate and some physiological characteristics in two barley cultivars, a pot experiment was conducted using a randomized complete block design as a factorial experiment with three factors including water stress, nitrogen fertilizer and barley cultivars in three replications. irrigation treatments conducted after anthesis at two levels of control (-3 bar) and drought stress (-13 bar). nitrogen fertilizer applied in control (non fertilizer application), first level (27 mg n/kg-1 soil) and second level (54 mg n kg-1 soil) in two barley cultivars differing in drought resistance (drought resistance abidar and drought susceptible cb-74-2). the results showed that drought treatment decreased photosynthesis rate, relative water content (rwc) and cell membrane stability under drought and heat stress, while drought treatment increased catalase and peroxidase activity. nitrogen treatment showed positive effects on photosynthesis rate, spad, rwc and cell membrane stability under heat stress. under irrigation treatment cb-74-2 showed the better performance in photosynthesis rate, rwc and enzymatic activity comprising to abidar cultivar, while under drought stress condition the decreasing of photosynthesis, rwc and cell membrane stability under heat stress were slower in abidar cultivar. this cultivar showed higher peroxidase activity under drought stress in contrast to irrigation treatment. under both control and water stress condition, a positive and significantly correlation found between grain yield and spad.