effect of seed priming by salicylic acid on some photosynthetic traits of cowpea under water deficit in flowering stage

effect of seed priming by salicylic acid and application of controlled water stress in flowering stage on some physiological characters such as relative water content, chlorophyll index, photosynthetic rates, transpiration rates, stomatal conductance, and leaf internal co2 concentration was investigated on cowpea (vigna unguiculata l. cv. parastoo) plants. experiment was done as a split block design with 3 replications in 2008-2009 at research farm of agriculture faculty, university of zanjan. factors were including controlled water stress as main plot in 2 levels (well watering and water shortage stress from initiation of flowering until 50% flowering of plot) and priming with salicylic acid as subplot factor in 5 levels involving 0, 900, 1800, 2700, 3600 µm. results showed that effect of water stress and salicylic acid was significant on physiological traits. water deficit reduced gas exchange and photosynthesis rate. on the other hand, seed priming enhanced relative water content, photosynthetic rates, transpiration rates, stomatal conductance and chlorophyll index compared to untreated plants. also, leaf internal co2 concentration was lower in this plants compared to untreated plants. it shows protective effects of salicylic acid against drought-stress. in general, among salicylic acid concentrations, 2700 µm treatment had the highest values in measured traits. in this treatment both in normal and stressed conditions photosynthesis rate was highest compared to untreated plants. in 3600 µm in all traits there was a decline compared to 2700 µm treatment. it shows that this hormone in higher concentrations has a preventing effect in physiological process.