NON-DESTRUCTIVE 3D VISUALIZATION OF SEEDS USING SYNCHROTRON RADIATION X-RAY TOMOGRAPHIC MICROSCOPY: NEW INSIGHTS INTO BRASSICACEAE SEED COAT STRUCTURES
Steinbrecher, T.1, Arshad, W.1, Pérez, M.1, Marone, F.2, Collinson, M.3 and Leubner-Metzger G.1
1Royal Holloway University of London, School of Biological Sciences, Egham, United Kingdom
2Swiss Light Source, Paul Scherrer Institute, Villigen, Switzerland
3Royal Holloway University of London, Department of Earth Sciences, Egham, United Kingdom
Potent high-resolution scanning technologies are currently being adapted to visualize seeds and reveal their internal structures. These technologies provide new tools to identify seed diseases and to give new insights into the seed’s internal structural morphology. The aim of imaging in biology is to localize and analyze structures in their native state. Conventional microscopy often requires fixation, dehydration and thin-sectioning of the samples. In contrast, hard X-rays with an energy of 10–100 keV are highly penetrating and provide non-destructive 3D visualization, high resolution quantitative investigations of biological samples. Synchrotron facilities like the Swiss Light Source (SLS) at the Paul Scherrer Institute bring tremendous advantages compared to traditional X-ray tomography with significantly higher resolution, short acquisition times, a better signal-to-noise ratio and quantitative reconstructions.
The seed coat represents the interface of the seed with the external environment and is an important component in the germination process as well as a key determinant of seed quality. Proanthocyanidins (PAs) are complex flavonoid compounds which confer a brownish color to the seed coat. Alterations of PAs can result in abnormal germination, loss of dormancy and premature sprouting. We used Synchrotron Radiation X-ray Tomographic Microscopy (SRXTM) at the beamline for TOmographic Microscopy and Coherent rAdiology experimentTs (TOMCAT) at the SLS to study the seeds of a unique set of distinct Lepidium sativum (Brassicaceae) accessions and the dimorphic seeds of Aethionema arabicum (Brassicaceae). The Lepidium accessions differ in their seed coat properties and PA contents leading to distinct germination behaviors. The dimorphism in Ae. arabicum is associated with several distinct anatomical, physiological and biomechanical differences between two fruit and seed morphs while the fruit ratios depend on the environmental conditions during seed development. The SRXTM provided cutting-edge 3D imaging and revealed physical seed coat properties. This allows investigation into the connection between PAs, biomechanical properties and the structure of the seed coat. The application of new promising technologies will help to reveal seed morphologies, to predict seed germination, and to develop new technologies with the ultimate goal to improve seed quality.