Roger M. Spanswick

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The electrical response of nitrate-grown maize (Zea mays L.) roots to 0.1 millimolar nitrate was comprised of two sequential parts: a rapid and transient depolarization of the membrane potential, followed by a slower, net hyperpolarization to a value more negative than the original resting potential. The magnitude of the response was smaller in roots of(More)
The effect of a number of inhibitors on the ATP level in single cells of Chara corallina has been measured using the luciferin-luciferase assay. The uncouplers of phosphorylation, carbonyl cyanide m-chlorophenyl hydrazone and 2,4-dinitrophenol, and the ATPase inhibitors, dicyclohexyl-carbodimide and diethylstilbestrol, all caused a marked reduction of the(More)
The H(+)/ATP stoichiometry was determined for an anion-sensitive H(+)-ATPase in membrane vesicles believed to be derived from tonoplast. Initial rates of proton influx were measured by monitoring the alkalinization of a weakly buffered medium (pH 6.13) following the addition of ATP to a suspension of membrane vesicles of Beta vulgaris L. Initial rates of(More)
Net fluxes of NH(4) (+) and NO(3) (-) into roots of 7-day-old barley (Hordeum vulgare L. cv Prato) seedlings varied both with position along the root axis and with time. These variations were not consistent between replicate plants; different roots showed unique temporal and spatial patterns of uptake. Axial scans of NH(4) (+) and NO(3) (-) net fluxes were(More)
Addition of sucrose to a solution bathing an excised developing soybean cotyledon causes a transient depolarization of the membrane potential, as measured using standard electrophysiological techniques. The magnitude of the depolarization is dependent on the concentration of both sucrose and protons in a manner which suggests carrier mediation; this process(More)
The initial rate of quenching of quinacrine fluorescence was used to monitor Mg:ATP-dependent H(+)-pumping in membrane vesicles from corn (Zea mays L. cv WF9 x MO17) roots and obtain a preparation in which vanadate-sensitive H(+)-pumping could be observed. Separation of membranes on a linear sucrose density gradient resulted in two distinct peaks of(More)
The proton-translocating, plasma membrane ATPase was purified from tomato roots. At the final stage of purification approximately 80% of the protein was found in a single band with an apparent molecular weight of 90 kilodaltons. Cross-linking studies indicated that the ATPase normally exists as a trimer of catalytic subunits. No evidence was found for any(More)
The effect of vanadate on the plant plasma membrane ATPase were investigated in plasma membrane fractions derived from corn roots (Zea mays L.) and red beets (Beta vulgaris L.). The K(i) for vanadate inhibition of the plasma membrane ATPase from corn roots and red beets was between 6 and 15 micromolar vanadate. In both membrane fractions, 80% to 90% of the(More)
Previously reported studies of cell ultrastructure and molecular probe passage in immature staminal hairs were extended to kinetic studies. The rate of transport of carboxyfluorescein into the cytoplasm in individual cells was monitored with a video analyzer and transport coefficients were determined. Carboxyfluorescein was found to traverse 5 cells in less(More)