Hydroponic experiments were conducted to compare photosynthesis and water status in rice leaves under normal conditions and drought stress simulated by addition of 10%, 20% and 30% polyethylene glycol (PEG6000). The results were listed as follows: 1) under drought stress, leaf photosynthesis, stomatal conductance, mesophyll conductance, total conductance, and chloroplastic CO2 concentration were decreased; 2)there was no significant difference in nonstomatal limitation under drought stress and normal conditions. But compared with normal conditions, stomatal limitation under 30% PEG simulated drought stress in Yangdao 6 and Shanyou 63 were increased by 42% and 81%, respectively; 3) there were positive relationships between photosynthesis and stomatal conductance, mesophyll conductance, total conductance and chloroplastic CO2 concentration; 4) under severe drought stress (20% and 30%), leaf water potential and water content were decreased significantly. And leaf water potential was positively correlated with stomatal conductance, mesophyll conductance and total conductance. Therefore, reduced chloroplastic CO2 concentration resulted from stomatal closure was the major limitation of photosynthesis. And the decreased leaf water potential may increase the internal CO2 transport resistance.
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