the effect of cadmium toxicity on changes of proline and antioxidant in lettuce

information of heavy metal toxicity about physiological aspect of lettuce is limited. therefore an experiment was conducted in crd designed with 7 replications on lettuce (lactuca sativa l.). treatments were cadmium in 3 concentration (0, 2 and 4 mg/l) added to hoagland solution. results were shown that increasing in cadmium of nutrient solution caused increasing in sod, pod antioxidant and proline contents of leaf tissues, in addition, cadmium decreased the amount of fresh weight and organic acid. applying 2 and 4 mg/l cadmium in nutrient solution produced pod, sod and proline around 8 and 53%, 55 and 106%, 39 and 119% in 2 and 4 mg/l cadmium, respectively. whereas in the same concentrations of cadmium protein decreased 25 and 5 %, respectively. under cadmium stress, toxic effects decline photosynthesis more than chlorophyll content.