Gravisensitivity of the acellular slime mold Physarum polycephalum demonstrated on the fast-rotating clinostat.

The acellular slime mold Physarum polycephalum was used to investigate a postulated general gravisensitivity of cells. Physarum was subjected i) to a rotation on the fast-rotating clinostat, which enables the simulation of weightlessness (0 g), and ii) to single horizontal turns of 180 degrees. On the fast-rotating clinostat the response consists of a frequency increase in radial contractile activity, an oscillation of the mean values (frequency regulation phenomena) and an increase in standard deviation. A combination of 0 g and respiration impediment inhibits the response to 0 g, i. e., the frequency increase in radial contractile activity during weightlessness simulation. Turning the specimens horizontally about 180 degrees in a normally positioned light microscope also leads to a frequency increase in radial contractile activity, but the temporal pattern of the frequency increase differs in comparison to the experiments performed on the clinostat during weightlessness simulation. These results demonstrate the occurrence of gravisensitivity in Physarum polvcephalum. Regulation phenomena and the possible role of mitochondria in graviperception are discussed.