Inhibition of ferric chelate reductase in alfalfa roots by cobalt, nickel, chromium, and copper

This research was initiated to examine the influence of metal cations on ferric chelate reducing capacity of alfalfa grown in hydroponic culture under conditions of iron sufficient or iron limited conditions. In the absence of added metal ions, ferric chelate reductase was greater in plants cultivated in iron limited conditions than in plants where iron was not limiting. Ferric chelate reductase activity in alfalfa roots was inhibited in both iron limited and iron sufficient growth by 0.5 to 2.5 muM Co2+. While the addition of Cr3+ at 2.0 muM slightly inhibited ferric chelate reductase in roots of plants grown under iron limited conditions, Cr3+ at 10 muM stimulated ferric chelate reductase in roots from both iron limited and iron sufficient media. Cu2+ additions at 5 muM to hydroponic media greatly inhibits ferric chelate reductase in plants with iron limited growth while shoot growth was inhibited in both iron sufficient and iron limited growth. The addition of Ni2+ at levels greater than 5 muM to alfalfa cultures inhibits both root and shoot growth; however, at these concentrations of Ni2+ ferric chelate reductase is stimulated in iron sufficient media but reduced in iron stressed plants. Acidification of the media was observed only with iron stressed cultures and did not closely correlate with levels of ferric chelate reductase of the roots.