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An investigation of the role of water stress condition on physiological characteristics 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 chlorophyll, prolin, soluble carbohydrates in water and alcohol of two grape cultivars
(Vitis vinifera) under water stress were studied. Water stress performed from 30th June till 5th
July 2003. Results showed temporary reduction in Pn, Tr and gs, under water stress conditions,
while the amount of Ci decreased during the first few days and then increased. Reduction in soil
water content caused reduction in leaf relative water content(RWC). During 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 from 6.95 to 0.38
(mmol/m2/s) in Rasheh and Khoshnav, respectively. Concentration of chlorophyl in either of
the cultivars was reduced, with reduction being higher in Rasheh cultivar. The amount of prolin
was increased in either one of the cultivars. Water stress had different effects on the amount of
alcohol soluble carbohydrates. Compared to Rasheh cultivar in which carbohydrate
concentration was reduced, it was increased in Khoshnav. The concentration of water soluble
carbohydrate was also compared. There was no change observed in Rashe, while reduction was
observed Khoshnav cultivar. The amount of gas exchange, chlorophyll, prolin and carbohydrate
indicated that Rasheh benefits from a higher resistance to water stress than Khoshnav cultivar.