Investigation the role of water stress condition on physiological properties of plant may provide means to understand bases of drought resistance. In one experiment the rate of photosynthesis(Pn), transpiration(Tr), leaf conductance(gs), internal Co2 concentration(Ci), the amount of chlorophyl, prolin, soluble carbohydrates in water and alcohol of two grape cultivar under the water stress were studied. Water stress performed from 30th jun till 5th july 2003. The results had been showed temporary reduction in Pn, Tr and gs, under water stress condition. While the amount of Ci was decreased during the first few days and then increased. Reduction of soil water content caused reduction in leaf relative water content(RWC). In this experiment during the water stress period, Pn was reduced from 7.32 and 7.21 (micro mol/m2/s) to 0 in rasheh and khoshnav cultivars, respectively. Also transpiration was reduced from 6.58 to 0.45 and 6.95 to 0.38 (mmol/m2/s) in rasheh and khoshnav, respectively. The concentration of chlorophyl in both cultivars was reduced. But such a reduction was higher in rasheh cultivar. The amount of prolin was increased in both cultivars. According to the results the water stress have different effect on amount of soluble carbohydrate in alcohol. Campared to reduction effect in Rasheh cultivar carbohydrate concentration was increased in Khoshnav. The concentration of soluble carbohydrate in water was compared. At the same situations the Rasheh have been showed no change but there was reduction in Khoshnav cultivar. The amount of gas exchange, chlorophyl, prolin and carbohydrate indicated that Rasheh hase higher resistance to water stress than Khoshnave cultivar.
