Effect of salt stress on photosynthetic characteristics in rice

Effects of salt stress on net photosynthetic rate,stomatal conductance,intercellular CO 2 concentration,chlorophyll content,photochemical efficiency of PSⅡ(Fv/Fm)and RuBP carboxylase activity in rice cultivars Pokkali(salt tolerant)and Peta(salt sensitive)were studied.The results showed that net photosynthetic rate,Fv/Fm,RuBP carboxylase activity and stomatal conductance decreased with increasing external NaCl concentration and prolonging the treatment time.Intercellular CO 2 concentration decreased in origin and then increased,but stomatal limitation value was contrary to intercellular CO 2 concentration.The contents of Chl,Chl a,Chl b and Chl a/Chl b first increased and afterwards decreased.The degree of increase or decrease of above mentioned parameters was lower in salt tolerant cultivars than that in salt sensitive ones.The cause of reduction of net photosynthtic rate in rice under salt stress might be mainly stomatal limitation in short period treatment and nonstomatal limitation in longperiod treatment.