Plasma Membrane H+-ATPase Activity in Spores, Germ Tubes, and Haustoria of the Rust FungusUromyces viciae-fabae

Abstract

Using plasma membrane-enriched vesicles, the properties of the H+-ATPase (EC 3.6.1.35) from the rust fungusUromyces viciae-fabaewere studied. The enzyme is strictly Mg2+-dependent and is inhibited by vanadate. The pH-optimum is at 6.7. By Western blot analysis using a monoclonal antibody against corn plasma membrane H+-ATPase a polypeptide of approximately 104 kDa could be detected. The vanadate-sensitive H+-ATPase activity of microsomal vesicles obtained from different stages of rust development was determined. Uredospores had only a very low enzyme activity (1.9 μmol Pi × mg−1protein × h−1). In germ tubes the ATPase activity was about twofold higher (4.0 μmol Pi × mg−1protein × h−1). An eightfold higher ATPase activity (16.1 μmol Pi × mg−1protein × h−1) was found in microsomal vesicles from haustoria which had been isolated from rust-infectedVicia fabaleaves. These results suggest, that the electrochemical gradient generated by the H+-ATPase of haustoria plays an important role for their function, possibly by promoting nutrient uptake from host cells.