Ca2+ transport in mitochondrial and microsomal fractions from higher plants

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Abstract
Mitochondria from etiolated corn possess a much greater Ca2+ uptake capacity per mg protein than microsomes from the same source. Differences in energy requirements, sensitivity to specific inhibitors, and sedimentation properties enabled us to study both Ca2+ uptake mechanisms without mutual contamination. The microsomal Ca2+ uptake does not vary much among different plants as compared to the mitochondrial Ca2+ uptake; this is also true for different organs of the same plant. Mitochondrial Ca2+ uptake is more dependent on the age of the seedlings than microsomal uptake, because of changes in active Ca2+ uptake activity rather than of changes in efflux. Intactness and the oxidative and phosphorylative properties of the mitochondria remained unchanged during this time period. Na+ and Mg2+ do not induce Ca2+ release from mitochondria.