Statoliths displacement in root statocytes in real and simulated microgravity

Despite the long-term employment of different types of clinostats in space and gravitational biology, the discussions about their reliability to mimic microgravity in space flight are still ongoing. In this paper, we present some data about the behaviour of amyloplasts-statoliths in root cap statocytes of higher plant seedlings growing during 3–5 days under slow and fast 2-D clinorotation and real microgravity in orbital flight. In addition, data on the displacement of amyloplasts in the statocytes of seedlings subjected to vibration and acceleration in the launch mode of a spacecraft are also given. A comparative analysis showed sharp differences in statolith responses to slow and fast clinorotation with a speed of 50 rpm. In the first case, the behaviour of amyloplasts was more or less similar to that in space flight, they did not touch the plasmalemma. In the second case, the contacts of statoliths with the plasmalemma or its invaginations (plasmalomasomes), like those under the action of vibration and acceleration, were clearly observed. Thus, slow 2-D clinostat is more suitable to study gravity sensing by root cap amyloplasts-statoliths and their responses to microgravity in the ground-based experiments.