Calcium and proton transport in membrane vesicles from barley roots

Journal Article · Sat Sep 01 00:00:00 EDT 1990 · Plant Physiology; (USA)

DOI:https://doi.org/10.1104/pp.94.1.179· OSTI ID:5946262

DuPont, F M; Windle, J J ^[1]; Bush, D S; Jones, R L ^[2]

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1. Department of Agriculture, Albany, CA (USA)
2. Univ. of California, Berkeley (USA)

Ca{sup 2+} uptake by membrane fractions from barley (Hordeum vulgare L. cv CM72) roots was characterized. Uptake of {sup 45}Ca{sup 2+} was measured in membrane vesicles obtained from continuous and discontinuous sucrose gradients. A single, large peak of Ca{sup 2+} uptake coincided with the peak of proton transport by the tonoplast H{sup +}-ATPase. Depending on the concentration of Ca{sup 2+} in the assay, Ca{sup 2+} uptake was inhibited 50 to 75% by those combinations of ionophores and solutes that eliminated the pH gradient and membrane potential. However, 25 to 50% of the Ca{sup 2+} uptake in the tonoplast-enriched fraction was not sensitive to ionophores but was inhibited by vanadate. The results suggest that {sup 45}Ca uptake was driven by the low affinity, high capacity tonoplast Ca{sup 2+}/nH{sup +} antiporter and also by a high affinity, lower capacity Ca{sup 2+}-ATPase. The Ca{sup 2+}-ATPase may be associated with tonoplast, Golgi or contaminating vesicles of unknown origin. No Ca{sup 2+} transport was specifically associated with the distinct peak of endoplasmic reticulum that was identified by NADH cytochrome c reductase, choline phosphotransferase, and dolichol-P-mannosyl synthase activities. A small shoulder of Ca{sup 2+} uptake in the plasma membrane region of the gradient was inhibited by vanadate and erythrosin B and may represent the activity of a separate plasma membrane Ca{sup 2+}-ATPase. Vesicle volumes were estimated using electron spin resonance techniques, and intravesicular Ca{sup 2+} concentrations were estimated to be as high as 5 millimolar. ATP-driven uptake of Ca{sup 2+} created 800- to 2,000-fold concentration gradients within minutes. Problems in interpreting the effects of Ca{sup 2+} on ATP-generated pH gradients are discussed and the suggestion is made that Ca{sup 2+} dissipates pH gradients by a different mechanism than is responsible for Ca{sup 2+} uptake into tonoplast vesicles.

• OSTI ID: 5946262
• Journal Information: Plant Physiology; (USA), Journal Name: Plant Physiology; (USA) Vol. 94:1; ISSN 0032-0889; ISSN PLPHA
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ALKALINE EARTH ISOTOPES
ALKALINE EARTH METAL COMPOUNDS
ALKALINE EARTH METALS
BARLEY
BARYONS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CALCIUM
CALCIUM 45
CALCIUM COMPOUNDS
CALCIUM ISOTOPES
CEREALS
DAYS LIVING RADIOISOTOPES
ELEMENTARY PARTICLES
ELEMENTS
EVEN-ODD NUCLEI
FERMIONS
GRASS
HADRONS
INTERMEDIATE MASS NUCLEI
ISOTOPE APPLICATIONS
ISOTOPES
LILIOPSIDA
MAGNOLIOPHYTA
MEMBRANE TRANSPORT
METALS
NUCLEI
NUCLEONS
PLANTS
PROTONS
RADIOISOTOPES
ROOTS
TRACER TECHNIQUES