Because in recent years many attempt to planting Pistacia khinjuk (Stock) seedlings in blank forest area in Zagross mountain region. Other hand a little information available on the impact of drought stress on physiological functions of Pistacia khinjuk Stocks seedlings. Therefore seedling of Pistacia khinjuk were subjected to drought stress but irrigation in four different time (every third day, every fifth day, every seventh day and every ninth day). Indicators such as; photosynthesis gas exchange, stomatal conductance, chlorophyll and praline content were monitored for the duration of the irrigation treatment. The obtained results indicated that the photosynthesis deceased in every ninth day irrigation and internal stomatal CO2 concentration from 280μmol μ-1 in every third day increased to 300.05μmol μ-1 in every ninth day. Stomatal conductance from 0.172μmol m-2 s-1 in every third day decreased to 0.012μmol m-2 s-1 in every ninth day irrigation treatment. Total Content of chlorophyll a, and chlorophyll b were varied. There were significantly differences between treatments for each parameter of chlorophyll. Variation in praline concentration between treatments was different and increasing concentration of praline occurred with increasing drought stress. Prolin might play a more complex role conferring drought resistance.
