Zinc toxicity in soybean grown at high iron concentration in nutrient solution

Iron (Fe) deficiency in plants may be caused by heavy metal toxicity and is expressed mainly by chlorosis in young leaves. Zinc (Zn) is often the heavy metal involved. The growth of soybean (Glycine max [L.] Merr.) in a 40 mu M Zn nutrient solution was studied using a factorial 2x2x2 experiment; two Fe (20 and 100 mu M), two S (0.02 and 20 mM), and two Fe foliar fertilization (with and without Fe-DTPA) levels. Lower dry matter yield, chlorosis in young leaves, and change in the periodic movement (light/dark) of unifoliate leaves were the main symptoms of Zn toxicity. Plants supplied with 100 mu MFe produced more dry matter than those supplied with 20 mu M and did not show leaf chlorosis, but still showed a change in the periodic movement of the leaves. A high Fe supply prevented most of the detrimental effects of toxic Zn. There was no effect of sulfur (S) on plant symptoms, and foliar fertilization with Fe-DTPA did not result in regreening of chlorotic leaves.