title: Identification of hydroxyl copper toxicity to barley (Hordeum vulgare) root elongation in solution culture.
abstract: The effect of pH on the acute toxicity of Cu to barley (Hordeum vulgare) root elongation was investigated in solution culture. The results showed that the median effective concentrations (EC50s; i.e., the concentration that reduced root elongation by 50% based on free Cu(2+) activity) were not significantly different in the low-pH range from 4.5 to 6.5, but in the high-pH range from 7.0 to 8.0, a significant effect of pH on EC50s was found. The nonlinear relationship between EC50 and H(+) activity in the present study indicated that the increased toxicity with increasing pH in solution may not be caused by decreasing H(+) competition. When we take account of CuOH(+) activities, a good linear relationship (r(2) > 0.97) between the ratio of CuOH(+) activity to free Cu(2+) activity and acute Cu toxicity to barley root elongation was achieved, which indicated that the observed toxicity in the high-pH range may be caused by CuOH(+) plus free Cu(2+) in solution. Linear-regression analysis suggested CuOH(+) had a greater binding affinity than Cu(2+) at the biotic ligand sites. The logistic dose-response curve showed that expressing the Cu dose as Cu(2+) + 2.92.CuOH(+) improved the data fit significantly compared to consideration of the free Cu(2+) activity only. Thus, our results suggest CuOH(+) was highly toxic to barley root elongation. The enhanced toxicity of CuOH(+) therefore needs to be considered when modeling the effect of pH on Cu toxicity to barley for exposures having pH greater than 6.5.
authors.affiliation: Ministry of Agriculture Key Laboratory of Plant Nutrition and Nutrient Cycling, The Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing, China.
authors.forename: Xuedong
authors.initials: X
authors.lastname: Wang
authors.forename: Yibing
authors.initials: Y
authors.lastname: Ma
authors.forename: Luo
authors.initials: L
authors.lastname: Hua
authors.forename: Mike J
authors.initials: MJ
authors.lastname: McLaughlin
mesh_terms: D003300:Copper / Q000633:toxicity*; D005659:Fungicides, Industrial / Q000633:toxicity; D001467:Hordeum / Q000187:drug effects* / Q000254:growth & development*; D006863:Hydrogen-Ion Concentration; D006878:Hydroxides / Q000633:toxicity*; D018517:Plant Roots / Q000187:drug effects* / Q000254:growth & development*; D012996:Solutions; D046509:Tissue Culture Techniques
chemical_list: D005659:Fungicides, Industrial; D006878:Hydroxides; D012996:Solutions; C508959:copper hydroxide; D003300:Copper