2017 ASHS Annual Conference

Non-destructive imaging is key to studying some processes in plants. Although various types of microscopy can be used without the necessity of slicing samples, the presence of opaque tissues or thickness of samples prevents light to go through and greatly reduces the capability or prevents the use of such methods. Previous studies have used x-ray phase-contrast imaging to visualize feeding and ice formation in insects. Initial 2D images of grapevine (Vitis spp.) were collected at the Cornell High Energy Synchrotron Source (CHESS). A 15 KeV, 7 mm × 7 mm monochromatic beam was used. Phase contrast is obtained when a highly parallel beam passes through the sample, in which density variations of the tissues slightly distort the wavefront. Interference with the unperturbed beam causes intensity recorded on 2D images. The distance between the sample and detector must be optimized for best contrast, which was found to be ~16 cm for our setup. The layered structures in the grapevine bud, as well as the similar densities in the layers made it difficult to discern the structures within the bud in a 2D image. Therefore, 3-dimensional reconstruction of the bud was proposed. Buds of different grapevine species (e.g. V. vinifera, V. amurensis), peach (Prunus persica), and cherry (Prunus avium), and a piece of V. ripariacane were imaged. In order to produce a 3D image, the buds were rotated 180 degrees, with images taken every quarter or third of a degree. For this, the buds were placed on a small goniometer and then mounted on a Huber 4-circle diffractometer. The maximum resolution of the 2D images was ~1 μm. Image sets were used for 3D reconstruction using Octopus Reconstruction (Inside Matters NV, Belgium). 3D renderings were produced using OsiriX (Pixmeo, Switzerland). This approach demonstrated to be useful to identify structures within a bud, as well as differences between species in the morphology of the bud. In the cane, different tissues were evident. Xylem vessels were prominent, likely due to the greater density of its walls. X-ray phase contrast imaging is a technique that can be very useful in studying morphology of small plant structures as a non-destructive method.