[Calcium as a control factor of nitrogenase activity in Vicia faba L. root nodules: calcium release from symbiosomes...

Treatment of root nodules or symbiosomes isolated from them with calcium chelator EGTA alone or with calcium ionophore A23187 for 3 h under microaerophilic conditions considerably decreased their nitrogenase activity (NA). Under these experimental conditions, cytochemical electron microscopy demonstrates a considerable calcium depletion in symbiosomes of the infected nodule cells by EGTA and A23187. Ca2+ channel blockers, verapamil and ruthenium red, inhibited EGTA-induced Ca2+ release from symbiosomes. In this case, NA insignificantly increased in the whole nodules and reached the baseline in symbiosomes. The experiments on isolated symbiosomes and arsenazo III demonstrated that verapamil inhibited Ca2+ transport induced by valinomycin at the background of K+ ions. These data suggest the presence of a verapamil-sensitive transporter on the peribacteroid membrane responsible for Ca2+ release from symbiosomes. A possible role of this transporter in the interaction between symbiotic partners in the infected cells of the root nodules is discussed.