The role of active Bradyrhizobium japonicum in iron stress response of soybeans

Abstract

The objective of this study was to identify the sites of H-ion exudation and Fe(III) reduction along both inoculated and non-inoculated roots of A7 and T203 soybeans. A split-root system was used in which half the roots of each plant were inoculated and actively fixing nitrogen and the other half were not.

Iron distribution through the developmental stages of Medicago truncatula nodules

“…10 These and other nodule ferroproteins are expressed at very high levels, to the extent that they induce the iron deficiency response in the host legume. 11 Consequently, the mechanisms involved in iron delivery to the symbiosome are critical for SNF.…”

Nutritional and management related interactions with iron-deficiency stress response mechanisms

“…However, in the absence of both N and Fe, T203 roots inoculated with Bradyrhizobium japonicum responded to Fe-deficiency stress by exuding both H+ and reductants and reducing Fe (Table 4). Iron reduction activity was exhibited just below the nodule clusters and H+ was released in association with active nodules (Terry et al 1991;Terry and Jolley 1994). In split-root experiments (Terry et al 1991), soybeans were nodulated by B. japonicum only on one half of the root system and H+ and reductant release appeared only on the nodulated side of T203 split-root systems.…”

“…Iron reduction activity was exhibited just below the nodule clusters and H+ was released in association with active nodules (Terry et al 1991;Terry and Jolley 1994). In split-root experiments (Terry et al 1991), soybeans were nodulated by B. japonicum only on one half of the root system and H+ and reductant release appeared only on the nodulated side of T203 split-root systems. In another split-root experiment, T203 soybean was inoculated with combinations of effective or ineffective strains of B. japonicum (Terry and Jolley 1994).…”

“…Both Fe-stress response and symbiotic N 2 fixation are biochemical reduction processes in the root which interact to enhance Fe-stress responses in soybean (Soerensen et al 1988;Terry et al 1991) and peanut (TelTY et al 1988). For example, T203 soybean normally fails to produce any Fe-stress response.…”

Metal Transport in the Rhizobium-Legume Symbiosis

“…This is particularly evident in the case of legumes since symbiotic nitrogen fi xation requires relatively high amounts of metals. Consequently, as the nodulation process is being initiated, it also triggers the "metal defi ciency response" (Terry et al 1991). In dicotyledonous plants, this response involves an acidifi cation of the surrounding soil to increase metal solubility, and the induction of metal reductases to reduce metals which are subsequently incorporated by epidermal metal transporters and also up-regulated (Puig et al 2007, Andaluz et al 2009, Bernal et al 2012).…”