Chlorophyll sorts out the good seeds from the bad

By Jonathan Beard A DEVICE that sorts seeds according to their ability to germinate could save farmers around the world millions of dollars. It does so by using a surprising marker to measure their ripeness: the seed’s chlorophyll content. Raoul Bino, head of reproduction technology at the Centre for Plant Breeding and Reproduction Research in Wageningen, the Netherlands, says his team was measuring the chlorophyll content of leaves when it made an accidental discovery. “Out of curiosity, we examined an old sample of cabbage seeds, which are brown. To our amazement, we found measurable quantities of chlorophyll in some seeds. We did not expect that at all.” Bino’s team is unsure what the chlorophyll does in the seed—but it is clear that it is not engaged in photosynthesis. “If you shine light on the chlorophyll in a seed, it does not transfer this energy to another molecule but instead re-emits it at another wavelength—meaning that it fluoresces,” says Bino. “This fluorescence can be measured. It is very simple. We are still astonished that no one before us ever discovered it, and then used it to sort seeds.” Bino has discovered that seeds retain their chlorophyll for many years, so long as they are kept dry. When they are moistened, the chlorophyll begins to break down: “Readiness to germinate and loss of chlorophyll go hand in hand,” says Bino, “the less chlorophyll, the riper the seed.” To measure the chlorophyll content, the Dutch researchers illuminate the seeds with red laser light, and measure the strength of the slightly longer-wavelength light that the chlorophyll re-emits. By identifying the optimal chlorophyll levels for ripeness, they have devised a reliable seed sorting method. The discovery is being commercialised by Satake USA, a company based in Houston,
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