HOW IS LEGHEMOGLOBIN INVOLVED IN PERIBACTEROID MEMBRANE DEGRADATION DURING NODULE SENESCENCE

An increase in the rate of succinate and glutamate uptake by isolated symbiosomes from French bean nodules was observed in the presence of i ron plus H2O2. The lipid bilayer, and not proteins involved in transpo rt, seems to be the major target of radical attack. Leghemoglobin in t he presence of a 6-fold excess of H2O2 (where heme breakdown and iron release occurred) provoked also an increase in peribacteroid membrane permeability. In contrast, this hemoprotein in the presence of a 2-fol d excess of H2O2 (where a protein radical was generated) was without e ffect. We suggest that in vivo the release of heme iron may constitute the major process concerning the involvement of leghemoglobin in the degradation of the peribacteroid membrane during nodule senescence,