Accumulation of copper by roots, hypocotyls, cotyledons and leaves of sunflower (Helianthus annuus L.)

The effects of different concentrations of copper sulfate on the growth of and the accumulation of Cu2+ by root, hypocotyl, cotyledon and leaf growth of sunflower (Helianthus annuus L.) were examined in this study. The concentrations of copper sulfate (CuSO4 • 5H2O) used were in the range from 10−5 to 10−3 M. Seedlings exposed to 10−5 M Cu2+ solution exhibited a 33% increase in growth (P<0.005) when compared with the root length of the control. The seedlings treated with 10−3 M Cu2+ were significantly inhibited in shoot growth (P<0.005). The Cu2+ content in roots, hypocotyls, cotyledons and leaves increased with increasing solution Cu2+ concentration. The roots of plants exposed to 10−3 M Cu2+ accumulated a large amount of Cu (1070 μg/g DW), and the Cu2+ level was approximately 25 fold higher than that of control. The Cu2+ contents in sunflower roots treated with 10−4 and 10−5 M Cu2+ were about 3.3 and 2.6 fold higher than the control, respectively. Also, the Cu2+ level of the roots exposed to 10−3 M Cu2+ was approximately 7.7 and 9.8 fold respectively, in comparison with the roots of plants grown in 10−4 and 10−5 M Cu2+. At 10−3 M Cu2+, the Cu accumulated mainly in the roots (about 73%), and small amounts of Cu2+ (27%) were translocated to the hypocotyls, cotyledons and leaves. The Cu2+ concentration in the roots was less than that of the above parts of seedlings in treated groups with 10−5–10−4 M Cu2+. H. annuus has potential ability to accumulate Cu without being overly sensitive to Cu toxicity.