Effect of the heavey metal of chromium on growth, bioaccumulation and oxidative stress induction on shoots of sunflower (Helianthus annuus)

Chromium (Cr) as the seventh most abundant element in the Earth crust، can enhance growth of plants in low concentrations. However، excess Cr is highly toxic to animals and plants. Chromium also can cause oxidative stress in plants by producing free radicals. In this research، effects of various concentrations of Cr on some growth parameters of sunflower (Helianthus annuus) ''s shoot were studied. Also، the effect of Chromium in inducing oxidative stress on the sunflower''s shoot investigated، as well. Cr treatments applied in six concentrations 0، 0. 001، 0. 01، 0. 1، 1، 5 and 10 mM on 4-week sunflower plants and one control group. Plants were allowed to grow under Cr treatments for three weeks before they were harvested. The results demonstrated that the 5 and 10 mM concentrations of Cr decreased the growth parameters of shoot (such as: fresh and dry weight، leaf area and also the length of stems)، whereas، the lower concentrations، no significant differences were shown compared to the control. MDA content of plants'' shoots significantly increased in 1، 5 and 10 mM concentrations of Cr. Shoot proline concentration was built up as Cr concentration increased in the treated plants، whereas، protein content decreased. Ascorbate content of plants decreased in 0. 1، 1، 5 and 10 mM concentrations of Cr، but، dehydroascorbate and total ascorbate increased. It was concluded that ascorbic acid can play a key role in the tolerance of sunflower against oxidative stress induced by chromium. Chromium accumulation in seeds، showed increase in 5 and 10 mM concentrations. Thus، it is so important to pay more attention to use safe edible plants for both humans and animals، as well.