Dynamic State of Water in Excised Ligustrum Lucidum Branches Observed by Dedicated Micro-Magnetic Resonance Imaging

Abstract

The dynamic state of water was investigated for tree branches by a combined k-space and q-space imaging method using a dedicated magnetic resonance imaging (MRI) device equipped with a 1.0-T permanent magnet. Changes in the 1H-NMR image due to the application of pulsed-field gradients (PFG) of stepping magnitude were measured using a phantom consisting of flow water and stationary water; the relationship between the flow velocities and the diffusion coefficients of water was studied. The method was applied to excised Ligustrum lucidum branches under conditions with and without weak light (100-140 μmol m-2 s-1). The distributions and diffusion coefficients of cell-associated water for individual tissues in the branches were determined in relation to morphology. Large amounts of water existed but diffusion coefficients were not high in the cambium. Though the water amounts were moderate, the highest diffusion coefficient exceeded that for pure water in the secondary xylem. The conduit tubes were smaller than the imaging pixel, unlike the phantom, so the determined values might be perturbed by the conditions of the ambient cell-associated water. However, positional responses in the xylem flow to light were detected, and a flow velocity up to 0.71 mm s-1 by transpiration was recorded. The movement of water in the phloem was not distinguished from large amounts of water in adjacent tissues, probably due to the very small cells and slow rates of flow in the phloem.