ATP-DEPENDENT ELECTROGENIC PROTON TRANSPORT AND TRANSLOCATION OF METABOLITES ACROSS THE PERIBACTEROID MEMBRANE OF LUPINE (LUPINUS-LUTEUS L)ROOT-NODULES

The symbiosomes and peribacteroid membrane vesicles isolated from Lupi nus luteus L. root nodules were used to investigate the ATP-dependent generation of membrane potential (Delta psi) and pH gradient (Delta pH ) across the peribacteroid membrane (PBM). Oxonol VI and acridine oran ge were employed as probes sensitive to Delta psi and Delta pH, respec tively. Based on the study of electrogenic and proton-translocation ac tivities of PBM, the ability of some metabolites mediating the interac tion between symbiotic partners to cross PBM was partially characteriz ed. The peribacteroid membrane ATPase was shown to operate as an elect rogenic proton pump; it created Delta psi in the absence of permeable ions and Delta pH in their presence. Vanadate was an effective inhibit or of both Delta psi and Delta pH formation, whereas nitrate converted Delta psi into Delta pH. These effects of inhibitors suggest that PBM of lupine nodules contains the P-type H+-ATPase, which is similar in its characteristics to the plasma membrane H+-ATPase of higher plants. Dicarboxylic acids, i.e., malate, succinate, and 2-oxoglutarate, elim inated Delta psi on PBM of symbiosomes that were preenergized by ATP o r artificial means. Similar elimination of Delta psi by dicarboxylates was observed in vesicle preparations of PBM. Dicarboxylic acids also induced rapid dissipation of the transmembrane pH gradient across PBM, no matter by which means the Delta pH was generated. Glutamate evoked rapid dissipation of the transmembrane pH gradient but had no effect on Delta psi. It is concluded that PBM of Lupinus luteus nodules is ca pable of transporting not only dicarboxylates but also glutamate.