“Reductants” Released by Roots of Fe‐Deficient Soybeans¹

Abstract

Abstract Iron‐stressed (deficient) ‘Hawkeye’ (HA) releases more “reductant” into nutrient solutions than PI‐54619‐5‐1 (PI) soybean [ Glycine max (L.) Merrill] roots. These two plants differ in their response to Fe stress and their susceptibility to Fe chlorosis. The objective of this study was to characterize the “reductant” and to determine its role in the uptake of Fe by HA and PI soybeans. Reducing capacity of the ‘reductant’ was determined by its ability to reduce ferric to ferrous iron. Fe 2+ was measured using 2,4,6,‐tripyrldyl‐s‐triazine (TPTZ) to form the color complex Fe 2+ (TPTZ) 2 . The reductant compounds were separated using paper chromatography (BAW‐4:1:5) and located on the paper as prussian blue spots after the papers were placed in ferricyanide‐ferrichloride solutions. Reductant from 16 HA reduced 90 μmoles (Fe 3+ to Fe 2+ ) compared to 5 μmoles for PI soybeans. The chelating agents HEDTA and DTPA (3 μmoles) decreased the reducing capacity from 1.8 μumoles Fe 2+ /ml concentrated reductant to 0.2 μmoles/ml. Adding more reductant partially overcome the interfering effects of the chelating agents. Adding the concentrated reductant to nutrient solutions increased the amount of Fe~+ iron in solution, but it did not increase the uptake of Fe by the plant. Something other than reductant in nutrient solution appears to be the controlling factor in the uptake of Fe by PI and HA soybeans. We believe the reductant can aid in releasing Fe from chelating agents to the root and that it can maintain Fe 2+ in the reduced state in the root. The latter may be its more important role in Fe nutrition.