Ca(2+) transport in mitochondrial and microsomal fractions from higher plants.

Mitochondria from etiolated corn possess a much greater Ca(2+) 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 Ca(2+) uptake mechanisms without mutual contamination. The microsomal Ca(2+) uptake does not vary much among different plants as compared to the mitochondrial Ca(2+) uptake; this is also true for different organs of the same plant. Mitochondrial Ca(2+) uptake is more dependent on the age of the seedlings than microsomal uptake, because of changes in active Ca(2+) 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 Mg(2+) do not induce Ca(2+) release from mitochondria.