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 fe rric chelate reducing capacity of alfalfa grown in hydroponic culture under conditions of iron sufficient or iron limited conditions. In the absence o f added metal ions, ferric chelate reductase was greater in plants cultivat ed in iron limited conditions than in plants where iron was not limiting. F erric chelate reductase activity in alfalfa roots was inhibited in both iro n limited and iron sufficient growth by 0.5 to 2.5 muM Co2+. While the addi tion of Cr3+ at 2.0 muM slightly inhibited ferric chelate reductase in root s of plants grown under iron limited conditions, Cr3+ at 10 muM stimulated ferric chelate reductase in roots from both iron limited and iron sufficien t media. Cu2+ additions at 5 muM to hydroponic media greatly inhibits ferri c chelate reductase in plants with iron limited growth while shoot growth w as 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 stress ed plants. Acidification of the media was observed only with iron stressed cultures and did not closely correlate with levels of ferric chelate reduct ase of the roots.