99220260 Spanswick This research is the continuation of a program designed with the long term objective of understanding transport in plant cells in terms of a chemiosmotic scheme for the transport of ions across plant cell membranes. The specific problem addressed in this proposal is that raised by the observation that the coupling between ATP hydrolysis and proton transport by ATPases from both the plasma membrane and the tonoplast appears to be variable depending, for example, upon the concentration of anions present in the membrane vesicle suspension. Hypotheses involving intrinsic u coupling between transport and ATPase activity ("slip") or electrically driven passive proton fluxes ("leak") will be tested by a variety of methods to account for the apparent discrepancy between anion stimulation of ATPase-mediated proton fluxes and of ATPase activity. %%% A proper distribution of salts between the inside and outside of a cell and the inside and outside of individual cellular compartments is critical for the normal function of all cells. The long term goal of this research is to understand the transport mechanisms for ions such as protons, potassium, and sodium (the components of salts) across the membranes of plant cells to maintain their normal distributions. This requires understanding the properties of the individual ion transport systems. A useful overall hypothesis for the mechanism of ion transport is based on a scheme in which the primary active transport systems are enzymes that transport protons (hydrogen ions) across cell membranes against an electrochemical gradient, using energy from hydrolysis of the energy-rich molecule, ATP. According to this scheme, other ions are transported by way of secondary systems that derive their energy from the electrochemical gradient of protons. (Transport of calcium ions across the plasma membrane is an exception.) The specific goal of this project is to study in some detail the relation between ATP hydro lysis and proton transport across the plant cell outer membrane and the membrane of an intracellular compartment, the tonoplast. The results of this research should provide a fundamental piece of the puzzle that in the long run will result in a complete understanding of how plants maintain their salt balance. ***
