The Use of Fura-2 Fluorescence to Monitor the Movement of Free Calcium Ions into the Matrix of Plant Mitochondria (Pisum sativum and Helianthus tuberosus)
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Media type:
E-Article
Title:
The Use of Fura-2 Fluorescence to Monitor the Movement of Free Calcium Ions into the Matrix of Plant Mitochondria (Pisum sativum and Helianthus tuberosus)
Contributor:
Zannoni, Davide
Published:
American Society of Plant Physiologists, 1993
Published in:
Plant Physiology, 102 (1993) 2, Seite 573-578
Description:
<p>
Purified mitochondria isolated from pea (Pisum sativum L. cv Alaska) stems and Jerusalem artichoke (Helianthus tuberosus L. cv OB1) tubers were loaded with the acetoxymethyl ester of the fluorescent Ca<sup>2+</sup> indicator fura-2. This made possible the continuous monitoring of free [Ca<sup>2+</sup>] in the matrix ([Ca<sup>2+</sup>]<sub>m</sub>) without affecting the apparent viability of the mitochondria. Pea stem mitochondria contained an initial [Ca<sup>2+</sup>]<sub>m</sub> of approximately 60 to 100 nM, whereas [Ca<sup>2+</sup>]<sub>m</sub> was severalfold higher (400-600 nM) in mitochondria of Jerusalem artichoke tubers. At low extramitochondrial Ca<sup>2+</sup> concentrations (≥100 nM), there was an energy-dependent membrane potential increase in [Ca<sup>2+</sup>]<sub>m</sub>; the final [Ca<sup>2+</sup>]<sub>m</sub> was phosphate-dependent in Jerusalem artichoke but was phosphate-independent in pea stem mitochondria. The data presented indicate that (a) there is no absolute requirement for phosphate in Ca<sup>2+</sup> uptake; (b) plant mitochondria can accumulate external free Ca<sup>2+</sup> by means of an electrophoretic Ca<sup>2+</sup> uniporter with an apparent affinity for Ca<sup>2+</sup> (K<sub>m</sub> approximately 150 nM) that is severalfold lower than that measured by conventional methods (isotopes and Ca<sup>2+</sup>-sensitive electrodes); and (c) [Ca<sup>2+</sup>]<sub>m</sub> is within the regulatory range of mammalian intramitochondrial dehydrogenases.
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