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.