Efficacy of the Random Positioning Machine as a Terrestrial Analogue to Microgravity in Studies of Seedling Phototropism

The future of space exploration will be contingent upon the use of plants in bioregenerative life support systems. Unfortunately, the microgravity of space can cause stress in plants, which can reduce growth. The Random Positioning Machine, RPM, is a device designed to provide an analogue for the effects of microgravity on Earth by rotating specimens in three dimensions. In this study, we compare the results from experiments conducted on the International Space Station with those conducted using the RPM (in the 3D clinostat mode) on the ground. Seedlings of Arabidopsis thaliana wildtype and phytochrome mutants were grown in true microgravity and in the omnidirectional gravity on a rotating RPM on the ground. We found that the RPM treatment caused less stress in the seedlings than did true microgravity. We also report that phytochromes A and B play roles in phototropic responses to unilateral light and that these roles differ in the two gravitational environments. Finally, we conclude that while root phototropism in unilateral red and blue differs significantly between the microgravity and omnidirectional stimuli, the RPM can serve as a reasonable analogue of microgravity conditions for assessment of shoot phototropism.