Transport Properties of the Tomato Fruit Tonoplast : I. Identification and Characterization of an Anion-Sensitive H-ATPase.
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 NO(3) (-), 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 K(m) 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 feasibility of isolating tonoplast vesicles from acidic fruit tissues for studies of transport activities associated with fruit development and maturation.
Oleski
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Mann Laboratory, Department of Vegetable Crops, University of California, Davis, California 95616.
Mahdavi
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P
Peiser
G
G
Bennett
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AB