Effects of Several Metals on Both Fe(III)‐ and Cu(II)‐Reduction by Roots of Fe‐Deficient Cucumber Plants

Abstract

The ferric‐chelate reductase induced by Fe deficiency is also able to reduce other ions such as Cu2+. This Cu(II)‐reduction has been less studied and it has been suggested that Cu2+ ion rather than Cu2+‐chelate serves as the substrate. Ferric‐chelate reductase activity is inhibited by some metals, but the mechanisms implicated are not known. In the present work we use Fe‐deficient cucumber seedlings to study the interactions of Cu2+, Ni2+, Mn4+, and Fe3+ on both Fe(III)‐reduction and Cu(II)‐reduction activities. The response of Cu(II)‐reduction activity to Cu concentration, in the presence or absence of citrate, was also studied. Results showed that inhibition of the ferric‐chelate reductase activity by Cu2+ or Ni2+ could be partially reversed by increasing the concentration of Fe‐EDTA. The Cu(II)‐reduction activity was even stimulated by Fe‐EDTA or Ni2+; it was inhibited by a high concentration of Cu2+ itself; and it was not affected by the absence of citrate. Mn4+ caused a moderate inhibition of both Fe(III)‐reduction and Cu(II)‐reduction activities. Results agree with the hypothesis that free Cu2+ ion is the substrate for Cu(II)‐reduction and suggest that the mechanisms involved in Fe(III)‐reduction and Cu(II)‐reduction could have some differences and be affected by metals in different ways. The mode of action of metals on the reductase activity are discussed, but they are still not well known.