3D Visualization of Maize Stem by MRI Technology

Abstract

Recent development in confocal and multi-photon microscopy allows 3D imaging of plant tissue in high resolution. However, other than physical sectioning, macroscopical study of plant organs in 3D remains a difficult task. Among various available technologies for macroscopical imaging (e.g., Xray macro-tomography, optical coherent tomography and MRI), MRI is an ideal choice for its contrasting modality in volumetric imaging of soft tissues. A 3T Biospect MRI system (Brucker, Germany)(FIG 1) equipped with a 6cm inner diameter micro-quadrature coil (FIG 2) for RF transmission and reception of MRI signals was used in this study. Spin echo based RARE sequence was used to obtain T2 weighted images with TR/TE = 3160.5/58.5ms and field-of-view of 1.67cm × 1.67cm (256 × 256 pixels) at a slice thickness of 0.8mm. This corresponds to a voxel size of 65 × 65 × 800μm. Data was obtained within 1/2 hour with number-of-excitations (nex) set at 16. Figure 4 (a-x) shows a series of MRI sections through a stem node (the node below the main ear insertion) from field-grown maize (Zea mays, van Odyssey sweet corn). The stem was fixed in 1:3 EtOH/acetic acid, washed thoroughly in water prior to imaging. Air bubbles trapped in the tissue were removed by vacuuming, to avoid imaging artifact due to low magnetic susceptibility of air. Figure 5 (a-g) shows reconstructed longitudinal sections. Three-dimensional reconstruction (FIG. 3) was performed by using Vaytek VoxBlast™ and AutoQuant’s AutoVisulize 3D™ software. in combination with image segmentation and tracing tools, the MRI technology will greatly enhance our capability in the understanding of vascular architecture and its development in plants.