Three-dimensional visualization of plant tissues and organs by X-ray micro-computed tomography.

Studies visualizing plant tissues and organs in 3D by micro-computed tomography (CT) published since approximately 2015 are reviewed. In this period, the number of publications in the field of plant sciences dealing with micro-CT have increased along with the development of high-performance lab-based micro-CT system as well as the continuous development of cutting-edge technologies at synchrotron radiation facilities. A widespread use of commercially-available lab-based micro-CT systems enabling phase-contrast imaging technique, which is suitable for visualization of biological specimens composed of light elements, appears to have facilitated these studies. Unique features of the plant body, which are particularly utilized for imaging of plant organs and tissues by micro-CT, are having functional air spaces and specialized cell walls, such as lignified ones. In this review we briefly describe the basis of micro-CT technology first and then get down into details of its application to 3D visualization in plant sciences, which are categorized as follows: imaging of various organs, caryopses, seeds, other organs (reproductive organs, leaves, stems and petioles), various tissues (leaf venations, xylems, air-filled tissues, cell boundaries, cell walls), embolisms, root systems, hoping that wide users of microscopes and other imaging technologies will be interested also in micro-CT and obtain some hints for deeper understanding of structure of plant tissues and organs in 3D. Majority of current morphological studies using micro-CT still appear to be at qualitative level. Development of methodology for accurate 3D segmentation is needed for transition of the studies at from qualitative level to quantitative level in the future.