Ca 2+ transport activity in mitochondria from some plant tissues

Abstract

Mitochondria isolated from some 14 different higher plants and fungi were examined for their capacity to carry out respiration-dependent accumulation of Ca 2+. Additions of Ca 2+ give little or no stimulation of state 4 respiration of plant mitochondria, although the added Ca 2+ was largely accumulated. Accumulation of Ca 2+ required phosphate and, in most cases, was stimulated by Mg 2+ and ADP or ATP. Ca 2+ uptake was abolished by respiratory inhibitors and uncoupling agents. The ratio of Ca 2+ ions taken up per pair of electrons per energy-conserving site was normal at about 2.0 for mitochondria from sweet potato and white potato; mitochondria from other plants showed somewhat lower ratios. Accumulated Ca 2+ was only very slowly released from previously loaded plant mitochondria. Respiration-inhibited sweet potato mitochondria show both high-affinity and low-affinity Ca 2+ binding sites sensitive to uncouplers, La 3+, and ruthenium red and thus resemble animal mitochondria. Most other plant mitochondria lack high affinity sites. In general, mitochondria from sweet potato and white potato tubers resemble those from animal tissues, but mitochondria from carrots, beets, turnips, onions, cabbage, artichokes, cauliflower, avocados, mung bean and corn seedlings, and mushrooms show rather low affinity and activity in accumulation of Ca 2+, probably due to lack of a specific Ca 2+ carrier.