Calcium Accumulation by Maize Mitochondria

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Abstract
The active accumulation of Ca, Mg, and phosphate by etiolated corn (Zea mays) shoot mitochondria was investigated. The necessary nergy for the accumulation of these ions was provided by either substrate oxidation or adeno-sine triphosphate (ATP). This accumulation was temperature-dependent and sensitive to pH. Substrate-supported uptake was depressed by the presence of adenosine diphosphate (ADP). Substrate-supported Ca uptake required phosphate but not exogenous Mg. Ca was necessary for carrier-free Ca45, Mg, or phosphate uptake. The ratio of divalent cation: phosphate accumulated was approximately 1 at low Ca concentrations. The ATP-driven Ca uptake required exogenous Mg and was stimulated by inorganic phosphate; the stimulation was reversed by the addition of ADP. Oligomycin inhibited ATP-supported Ca uptake but had no effect on substrate-supported Ca uptake. Dinitrophenol and chloramphenicol inhibited with either energy source. The data suggest that a phosphorylated high energy intermediate of oxidative phosphorylation participates in the accumulation of divalent ions and phosphate by corn mitochondria.