Role of Organic Acids in Sunflower Tolerance to Heavy Metals

Exposure of Helianthus annuus L. seedlings to Al³⁺, Cd²⁺ or Zn²⁺ resulted in a marked decrease of fresh and dry masses of the shoots and the roots. The increase of Al³⁺, Cd²⁺ or Zn²⁺ uptake was accompanied by a significant decrease of nitrate, phosphorus and K⁺ uptake. There was a significant increase of malic and citric acid contents in the shoots and roots of heavy metal-treated seedlings whereas the change in fumaric acid was insignificant. Al³⁺ and Zn²⁺ alone stimulated excretion of malic and citric acids to the rhizosphere. Addition of high concentrations of malic or citric acid alleviate to some extent the inhibitory effect of Al³⁺ and Zn²⁺ on plant growth. This revised version was published online in July 2006 with corrections to the Cover Date.