Cations stimulate proton pumping in Catharanthus roseus cells: implication of a redox system?

Abstract During growth, cultured Catharanthus oseus cells produce a transient acidification of the culture medium that may be controlled by cations. The removal of divalent ions from the medium by the chelator EGTA resulted in an inhibition of this acidification. Conversely, acidification can be stimulated by the addition of Ca²⁺, Mg²⁺ and La³⁺ in the basal medium. This acidification process and the proton-linked redox pump previously described (Marigo & Belkoura, 1985) respond in a similar manner to cations. These two systems, which are both inhibited by the Ca²⁺ -calmodulin antagonist calmidazolium, could be regulated by the Ca²⁺-calmodulin complex. By using ionic surfactant (CP⁺, SDS^?) it was demonstrated that the net surface charge of the plasmalemma plays a role in the activation of the two pumping processes. These results are interpreted to indicate that a transmembrane redox system could provide the energy for electrogenic proton extrusion.