Competition Between Phosphate and the Plant for Fe from Fe 2+ Ferrozine 1

Much has been written about how phosphate accentuates Fe deficiency in plants; but little attention has been given to the genotype of rootstock as a controlling factor in Fe uptake. The important role of the plant was studied in these experiments. Competition between phosphate, the plant, and ferrozine for Fe in nutrient solution was examined. Feinefficient and Fe efficient varieties of soybeans [ Glycine max (L.) Merr.] ( Lycopersicon esculentum Mill.) were used as test plants because they differ, respectively, in their ability to tolerate P and to reduce Fe 3+ to Fe 2+ at the root. Within 2 days after adding 16 ppm of P to the nutrient solution, only about 10% of the Fe 2+ ferrozine was colorimetrically detected in solution. The Fe was removed from Fe 2+ ferrozine, and it appeared in the solution as a suspension of iron‐phosphate. Phosphate was dominating the system for Fe. Four days later, the plants developed Fe deficiency (Fe stress). Fe‐efficient plants responded to Fe stress by releasing more H + into solution and reducing more Fe 3+ to Fe 2+ than was reduced by Fe‐inefficient plants. As this occurred, Fe 2+ ferrozine reappeared in solution. The Fe‐efficient plants now dominated the system for Fe. On day 17 (final harvest), the green top leaves of Fe‐efficient HA soybeans contained 86 ppm of Fe, whereas the chlorotic top leaves of Fe‐inefficient PI soybeans contained only 36 ppm Fe. In the latter, phosphate still dominated the system for Fe because the reducing capacity (Fe 3+ to Fe 2+ ) of the Fe‐inefficient plants was not great enough to overcome the effects of phosphate.