Researchers used Diamond Light Source, United Kingdom’s synchrotron facility, to document for the first time the rate of evolution of seed coat thinning on 4000-year-old samples, which is a major marker of crop domestication, present in archaeological remains of crop seeds.
The seed used for the study was of a legume horse gram (Macrotyloma uniflorum), a bean commonly eaten in southern India. Using the high-resolution X-ray computed tomography (HRXCT) technique on DLC’s I13-2 beamline the researchers were able to measure for the first time the coat thickness throughout the entire seed and present evidence for seed coat thinning between 2000 BC and 1200 BC. Diamond Light Source works like a giant microscope, harnessing the power of electrons to produce bright light and perform real space imaging and tomography. The beamline can image samples of 0.1-10 mm thickness at spatial resolutions that can extend a little beyond a micron. Scientists state that thinner coats will mean faster germination of a seed when it is watered and conventional methods require breaking and destroying archaeological specimens but this new technique allows to measure the thickness in a non-invasive way. The beamline has enabled the team to produce 3D images of the seeds with incredible micrometer scale resolution, without damaging their precious samples. This is the first time that HRXCT has been applied to entire archaeological seeds, with results suggesting that previous spot measurement thickness tests could be misleading. The results indicated that domestication of horse gram took place during the second millennium BC, with seed coats fair fixed in thickness by the early centuries AD.
(after EurekAlert! & Diamond Light Source)