Effects of Low Temperature and Respiratory Inhibitors on Calcium Flux in Plant Mitochondria

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Abstract
The effects of low temperature on uptake and release of 45Ca2+ were studied with sound, well-coupled mitochondria extracted at room temperature from avocado (Persea americana Mill, cv Fuerte) fruits. Low Ca2+ concentrations (10 micromolar) were employed to simulate physiological conditions. At 25°C, the rate of Ca2+ uptake decreased with time, whereas at 5°C the initial rate, though lower, remained linear. As a consequence total uptake at 5°C was substantially greater than at 25°C for periods greater than 5 min. Preincubation of mitochondria at 5°C enhanced subsequent Ca2+ uptake at 25°C. Ca2+ uptake was inhibited by carbonyl cyanide-m-chlorophenyl hydrazone (CCCP) and by ruthenium red, but neither KCN nor salicylhydroxamic acid separately or together had any major inhibitory effect. Preloaded mitochondria held for 60 min in a Ca-free medium lost little Ca2+ at 25°C and none at 5°C, except in the presence of ruthenium red or CCCP.