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PP i ase‐Activated ATP‐Dependent H + Transport at the Tonoplast of Mesophyll Cells of the CAM Plant Kalanchoë daigremontiana *
Author(s) -
MarquardtJarczyk Gisela,
Lüttge U.
Publication year - 1990
Publication title -
botanica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.871
H-Index - 87
eISSN - 1438-8677
pISSN - 0932-8629
DOI - 10.1111/j.1438-8677.1990.tb00149.x
Subject(s) - atp hydrolysis , vacuole , vesicle , chemistry , proton transport , atpase , biophysics , electrochemical gradient , kalanchoe , membrane transport , atp synthase , chemiosmosis , nigericin , quenching (fluorescence) , diaphragm pump , biochemistry , membrane , enzyme , fluorescence , biology , thermodynamics , cytoplasm , botany , physics , volumetric flow rate , quantum mechanics
The co‐ordinated action of the two proton‐transporting enzymes at the tonoplast of the CAM plants. daigremontiana , viz. the ATPase and the PP i ase, was studied by measuring fluorescent dye quenching. The initial rates of ATP and PP i ‐dependent H + transport into tonoplast vesicles were additive, i.e. the sum of the rates obtained with each substrate alone was in the range obtained with both substrates added together at the same time. Conversely, the activities of the two H + pumps were non‐additive in establishing the steady‐state level, indicating that the final steady state was under thermodynamic control of a maximal attainable proton gradient. The initial rates of ATP‐dependent H + transport were stimulated enormously if ATP was added a few minutes after pre‐energization of the vesicles with PP i . This stimulation was observed only when the PP i ase was active. A similar effect was not found for PP i ‐dependent H + transport after pre‐energization with ATP. Hence, a PP i ase‐activated ATP‐dependent H + transport can be distinguished from the basic ATP‐ and the basic PP i ‐dependent H + transport. In parallel a PP i ‐dependent stimulation of ATP hydrolysis in the absence of ionophores was measured, which can only be attributed to the activity of the PP i ase. PP i ase‐activated ATP‐dependent H + transport depends on the presence of permeant anions. It shows properties of both H + transport activities, i.e. the chloride and malate stimulation and the DCCD inhibition of the ATP‐dependent H + transport activity, the nitrate stimulation and the KF inhibition of the PP i ‐dependent H + transport activity. Only MgPP i and MgATP were effective as the respective substrates. The PP i ase‐activated ATP‐dependent H + transport had a half life of about 5–9 minutes. It is concluded that the PP i ase may play an important role in kinetic regulation of the ATPase, and implications for CAM metabolism are discussed.