The influence of osmotic stress on the content of calcium ions in the red beet vacuoles and on the transport activity of tonoplast proton pumps

The contents of calcium ions in the isolated vacuoles and in intact red beets under the conditions of dormancy and osmotic stress was determined. It is demonstrated that the content of calcium ions in the red beet vacuoles not exposed to osmotic stress makes 13.3% of the total content these ions in intact red beets. Under the conditions of osmotic stress, this indicator increases substantially. Furthermore, under the conditions of hyperosmotic stress, the content of calcium ions in the vacuoles was 30%, while under hypoosmotic stress it was 49% of the total content of these ions in the intact red beet. The transition of calcium ions from the cytoplasm and other compartments into the vacuole under the conditions of osmotic stress is, probably, one of forms of participation of the vacuole in adaptation processes of the plant cell under this kind of abiotic stress. It has been demonstrated for the first time that tonoplast proton pumps, which actively participate in provision of calcium homeostasis in cytoplasm, substantially activate their transport activity under osmotic stress, what allows one to speak about their important role in the cell’s protective programs. Under normal (no stress) conditions, artificial elevation of the content of calcium ions led to inhibition of activity of the tonoplast proton pumps, while under gipoosmotic stress the activity of tonoplast proton pumps increased, what might aid to restoring homeoctasis with respect to calcium ions in cytoplasm