Transport Properties of the Tomato Fruit Tonoplast

Abstract

An anion-sensitive H+-translocating ATPase was identified in membrane vesicles isolated from mature green tomato (Lycopersicon esculentum) fruit. The H+-ATPase was associated with a low density membrane population having a peak density of 1.11 grams per cubic centimeter, and its activity was inhibited by NO3-, N,N''-dicyclohexylcarbodiimide and diethylstilbestrol but not by vanadate, azide, molybdate, or oligomycin. This H+-ATPase has an unusual pH dependence indicating both a slightly acidic and a near neutral peak of activity. Chloride was found to be a potent stimulator of ATPase activity. The Km for the H+-ATPase was approximately 0.8 millimolar ATP. The characteristics of this H+-ATPase are very similar to those described for a number of plant cell tonoplast H+-ATPases suggesting that the activity identified in tomato fruit membranes is tonoplast-associated. This report demonstrates the feasbility of isolating tonoplast vesicles from acidic fruit tissues for studies of transport activities associated with fruit development and maturation.