Beneath the skin of our seeds - how X-ray analysis helps conservation
X-ray analysis helps Kew to make sure that seeds saved in the Millennium Seed Bank are of the highest quality.
A sample of Terminalia brachystemma fruits. Although the fruits all appear to be healthy, six contain empty seeds
An X-ray gives a clear image of the internal morphology of the seed or fruit. The X-rays are generated using very low voltages (much lower than are used for most medical applications) and the method is thus safe with the appropriate precautions. This aside, because the seeds may have been subjected to some genetic damage, the sub-sample is usually discarded, though sometimes it is used for germination testing.
Before starting the procedure, the seed collections to be X-rayed may be sorted into groups according to the size and thickness of their seed/fruit coats. Each group may then be X-rayed using the same shelf position in the Faxitron digital X-ray machine. Shelf position determines the magnification of the image.
The seed samples to be X-rayed are laid out in Petri dishes or plastic grids with machine-punched holes set in a regular pattern, backed with waxed paper.
Of particular interest are the outwardly normal, but 'empty' seeds that regularly occur in collections of wild species. Allowance must be made for this incompetent fraction of the collection when germination and seed quantity are determined.
Insect larvae living within seeds are sometimes unmasked by this technique. The image right shows Adesmia balsamica seeds with infestation.
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