Visualization of Arabidopsis root system architecture in 3D by refraction-contrast X-ray micro-computed tomography
Plant roots change their morphological traits in order to adapt themselves to different environmental conditions, resulting in alteration of the root system architecture. To understand this mechanism, it is essential to visualize morphology of the entire root system. To reveal effects of long-term alteration of gravity environment on root system development, we have performed an experiment in the International Space Station using Arabidopsis (Arabidopsis thaliana (L.) Heynh.) plants and obtained dried root systems grown in rockwool slabs (mineral wool substrate). X-ray computer tomography (CT) technique using an industrial X-ray scanner has been introduced for the purpose to visualize root system architecture of crop species grown in soil in 3D non-invasively. In the case of the present study, however, root system of Arabidopsis is composed of finer roots compared with typical crop plants and rockwool is also composed of fibers having similar dimension to that of the roots. A higher spatial resolution imaging method is required for distinguishing roots from rockwool. Therefore, in the present study, we tested refraction-contrast X-ray micro-CT using coherent X-ray optics available at the beamline BL20B2 of the synchrotron radiation facility SPring-8. Using this technique, both the primary and the secondary roots were successfully identified in the tomographic slices, clearly distinguished from the individual rockwool fibers and resulting in successful tracing of these roots from their basal regions. This newly-developed technique should contribute to elucidate the effect of microgravity on Arabidopsis root system architecture in space.