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), Vol. 94:1; ISSN 0032-0889
• Country of Publication: United States
• Language: English

Related Subjects

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