Heavy metal stress is one of the important abiotic stresses limiting plant growth and yield. Cd is a heavy metal that enters the environment through industrial wastewater, phosphate fertilizers and sewage sludge and is easily absorbed by plants. There are various methods to reduce the effects of cd toxicity. One of the methods to increase tolerance of plants to adverse stress conditions is the use of plant organic compounds. Moringa leaf extract as an organic compound can prevent many damaging processes in stress condition. To investigate the effect of cd toxicity and leaf extract of Moringa olifera on physiological and morphological characteristics of pistachio seedlings, a factorial (4×3) experiment was conducted. The treatments consisting of four levels of Cd (0, 5, 10 and 20 mg per kg of soil) from source of cadmium chloride and leaf extract of M. oleifera in three levels [0 (distilled water), 20 and 30 times diluted], in a completely randomized design with four replications. In this experiment, changes in chlorophyll, carotenoid and oxidative stress indices including electrolyte leakage (EL), chlorophyll fluorescence, malondialdehyde (MDA), proline content, hydrogen peroxide (H 2 O 2 ), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) activities, Cd concentration of shoot and also morphological characteristics were measured. Results showed that increasing Cd concentration decreased vegetative growth parameters such as stem length, leaf number, leaf specific area and root dry weight and root length of pistachio seedlings. Application of M. oleifera foliar extract reduced the adverse effects of Cd toxicity and improved vegetative growth parameters. Increasing Cd concentration significantly increased electrolyte leakage indices, MDA, H 2 O 2 and proline content in pistachio leaves. Application of M. oleifera leaf extract at 30 times diluted concentration significantly increased proline content. The activity of CAT and APX and GR enzymes Cd increased at the highest level compared to control. M. oleifera leaf extract significantly reduced concentration of shoot Cd, electrolyte leakage, CAT activity, MDA and H 2 O 2 contents compared to control, but it increased the activity of GR. With increasing Cd concentration in soil, the amount of chlorophyll fluorescence, carotenoids and chlorophyll a/b ratio decreased by 7.99%, 40.74% and 4.46% compared to control, respectively . M. oleifera leaf extract reduced the damage caused by Cd toxicity by inhibiting the decreases of chlorophyll fluorescence and carotenoid content and photosynthetic pigments. Key words Cadmium, Moringa leaf extract, Pistachio, Oxidative stress.
