Sites of Iron Reduction in Soybean Plants¹

Abstract

Abstract Reduction of iron (Fe 3+ → Fe 2+ ) at the root of Glycine max . (L.) Merrill var. Hawkeye soybean was studied to identify areas of reduction in the root. Sites of iron reduction were indicated by the formation of a Prussian or Turnbull's blue precipitate. This blue precipitate formed whenever the iron in either FeEDDHA or potassium ferricyanide was reduced by the plant. Where FeEDDHA and potassium ferricyanide were supplied together in the nutrient solution, a blue precipitate appeared in epidermal areas. This precipitate appeared in the endodermal areas of the root when FeEDDHA was supplied to the plant 20 hours before placing them in a ferricyanide solution. Reduction was most pronounced between the regions of root elongation and root maturation at both the epidermis and the endodermis. Reducing capacity was greatest in the young lateral diarch roots indicating that these roots contribute significantly to the ability of the plant to take up iron. A reductant which exuded from the roots of an irondeficient plant was capable of reducing approximately 360 µg of inorganic iron. The ability of some plants to reduce iron may partially explain why they can obtain iron from synthetic chelates and can utilize iron in calcareous soils more effectively than other plants.