Structural anisotropy in celery stalks by microscopic MRI and polarized light microscopy

Structural anisotropy of celery stalks was studied using T ₂ anisotropy in microscopic MRI (μMRI) and supplemented by quantitative polarized light microscopy (PLM) at optical resolutions. Parenchyma, which is the ground tissue in celery and has a diameter in the range of 50–90 μm, was found to have isotropic T ₂; in contrast, collenchyma, which is the structural part of the ground tissue in celery and has a diameter in the range of 8–12 μm, was found to have strong anisotropic T ₂. Substantial size variations within each porous structure and substantial co-existences of more than one type of structural tissues within a single μMRI voxel were noticed in the optical images, which can contribute to the less clear anisotropies in the smaller vascular structures (e.g., phloem (approximately 2–6 μm in diameter) and xylem (approximately 5–15 μm in diameter)). Celery could be used as a simple plant model to study the relationships between tissue microstructures and nuclear spin relaxation in fibrous and porous specimens.