Effect of Lead Stress on Photosynthetic Characteristics and the Activity of Antioxidant Enzymes in Wheat Seedling

A hydroponic experiment was carried out to investigate the effect of different Pb levels on photosynthetic characteristics and the activity of antioxidant enzymes in wheat seedlings.The results showed that,with the increase of lead concentration,the net photosynthetic rate(Pn),transpiration rate(Tr),both stomatal conductance(Gs) or photosynthetic pigment content(SPAD) increased firstly and dropped afterwards,while intercellular CO2 concentration(Ci) firstly dropped and increased afterwards,both reaching the maximum or minimum under 100 mg/L treatment of Pb concentration.The results also showed that decrease of photosynthesis was caused by both stomatal factors and non-stomatal factors;with the increase of lead concentration,the SOD activities increased in the beginning and then fell,while the CAT and POD activities increased all the time,the MDA content rose significantly when pb level reached 200 mg/L and 300 mg/L,which suggested that the membrane system of wheat seedling was damaged by lead stress.