Influence of inhibitors of alternative respiration pathway and oxygen on growth and proton secretion

A possible involvement of the alternative oxidase pathway in proton translocation was investigated. Net H+ efflux- and elongation-rates were simultaneously and continuously measured by means of a pH-stat and an angular position transducer. Disulfiram, an inhibitor of the alternative path, reduces the IAA- and Fusicoccin-induced as well as endogenous proton secretion and growth. Fusicoccin-induced H+ secretion is very sensitive to reduced oxygen concentration values far apart from the Km of cytochrome oxidase. The sensitivity of non stimulated proton secretion to reduction of oxygen concentration depends on the age of plant material. It is proposed that more than one system is responsible for proton translocation across the plasmalemma. One of them has a high sensitivity to reduced oxygen concentration which is within the same range of the high Km value of the alternative oxidase.