effects of nitrogen and arsenic on photosynthetic pigments, antioxidant enzyme activities and nutrient elements content in safflower (carthamus tinctorius l.) se

introduction and aim: arsenic is a metalloid toxic for plants. arsenic is polluting the environment through the natural and artificial resources. it is harmful to human health. arsenic in plants for the production of the reactive oxygen species (ros) lead to destruction of nucleic acids and proteins in tissues of plants. it also reduces of photosynthesis and growth by destroy of the membranes of chloroplasts. the arsenic-contaminated soil cleanup is an important issue in the study of biology. in order to investigate the effects of different concentrations of arsenic and nitrogen fertilizer on photosynthetic pigments, antioxidant enzyme activities and nutrient concentrations in both shoot and seed of safflower plants (cv. goldasht). materials and methods: to implement of this study, a plot experiment was conducted in a factorial design as randomized complete block with three replicates in university of zabol. arsenic treatment included: a1= control or without application of arsenic, a2=30, a3=60 and a4=90 mg. kg-1 soil from the na2haso4 source and three nitrogen levels including w1=75, w2=150 and w3=225 kg.ha-1 from urea source.results: the results showed that arsenic treatment had a significant effect on the antioxidant enzymes activity. among the three antioxidant enzymes, by increasing arsenic level from control (a1) to 90 mg. kg-1 soils (a4), the activity of ascorbate peroxidase (apx) decreased and the activities of gayacol peroxidase (gpx) and catalase (cat) increased. arsenic treatment had no significant effect on the photosynthesis pigments included chlorophyll a, b and cartoneid content in leaves. among the elements content in shoot and seeds, arsenic treatment had only significant effect on the potassium and sodium content in shoot of safflower plants. nitrogen and interaction between arsenic and nitrogen treatments, except on ascorbate peroxidase (apx), had significant effect on catalase (cat) and gayacol peroxidase (gpx). the highest gayacol peroxidase (gpx) activity was obtained at a4n3 treatment. however nitrogen treatment had significant on the content of chlorophyll a, b and cartoneid in leaves and increased them, but by increasing nitrogen level from n1 to n3, the content of potassium in seed increased and the content of sodium in seed was decreased. conclusion: the results obtained from this experiment showed that, application of heavy metal element (arsenic) however adversely effect on safflower plants but until to 30 mg arsenic per kg of soil, it had not adversely effects on growth and physiological characteristics of safflower (cv. goldasht). the adversely effect of arsenic was appeared at the higher levels of 30 mg arsenic per kg of soil.