Distribution of Calcium Ions in Cells of the Root Distal Elongation Zone Under Clinorotation

Currently, calcium ions are known to play a crucial role in the vital activity of plant cells and in stimulus–response coupling for many environmental signals, altered gravity included. The available data on changes in Ca^2?+? distribution and concentration in the cells of different organisms influenced by altered gravity allow to suggest that microgravity affects the calcium messenger system, and provide new insight for the understanding of calcium-and gravity-dependent cellular processes. We have studied with confocal microscopy the distribution and relative content of calcium ions in the Beta vulgaris root distal elongation zone cells grown under slow horizontal clinorotation, reproducing one of the microgravity particularities, namely the absence of an orienting action of the gravity vector, compared to control conditions. We demonstrate that Ca^2?+? relative content is 1.3 times higher in the roots of seedlings grown upwards and 1.2 times higher in the seedlings grown downwards compared to the control. Based on obtained data, taking into account the specific physiological properties of cells in the distal elongation zone, it is supposed that, under clinorotation, enhanced Ca^2?+? relative content affects Ca^2?+?-dependent cytoskeleton reorganization involved in cell gravisensing in altered gravity.