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Fe^III Reduction in Cell Walls of Soybean Roots ¹

Department of Biochemistry and Biophysics, Iowa State University, Ames, Iowa 50011

Reduction of Fe^IIIEDTA by excised roots of soybean seedlings (Glycine max L.) is stimulated by L-malate in the bathing solution. Reduction occurs much more rapidly with roots of seedlings grown in the absence of iron than with roots of seedlings grown with iron. Cell-wall preparations from these roots catalyze reduction of Fe^IIIEDTA by NADH. They also contain NAD⁺-dependent L-malate dehydrogenase. Enzymic activity of the cell-wall preparations is not affected by previous iron nutrition of the plants, but the amount of L-malate in the roots is increased when seedlings have been deprived of iron. We propose that reduction of iron before absorption by soybean roots occurs in the cell-wall space, with L-malate secreted from the roots serving as the source of electrons. Part of the iron reductase activity of the cell walls can be solubilized by extraction with 1 molar NaCl. The enzyme has been partially purified.