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).
abstract: 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 Ca2+ indicator fura-2. This made possible the continuous monitoring of free [Ca2+] in the matrix ([Ca2+]m) without affecting the apparent viability of the mitochondria. Pea stem mitochondria contained an initial [Ca2+]m of approximately 60 to 100 nM, whereas [Ca2+]m was severalfold higher (400-600 nM) in mitochondria of Jerusalem artichoke tubers. At low extramitochondrial Ca2+ concentrations ([greater than or equal to]100 nM), there was an energy-dependent membrane potential increase in [Ca2+]m; the final [Ca2+]m 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 Ca2+ uptake; (b) plant mitochondria can accumulate external free Ca2+ by means of an electrophoretic Ca2+ uniporter with an apparent affinity for Ca2+ (Km approximately 150 nM) that is severalfold lower than that measured by conventional methods (isotopes and Ca2+-sensitive electrodes); and (c) [Ca2+]m is within the regulatory range of mammalian intramitochondrial dehydrogenases.
authors.affiliation: Department of Biology, Biochemistry Laboratory, University of Bologna, Via Irnerio 42, 40126 Bologna, Italy.
authors.forename: M.
authors.initials: M
authors.lastname: Zottini
authors.forename: D.
authors.initials: D
authors.lastname: Zannoni