Thermal Fingerprint Saves Seeds and Time

Scientists from UK and Austria have developed a new way to find out whether seeds are dead or alive, without killing them!

It’s one of the frustrating realities of seed testing that the best way to find out if a seed is still viable is to kill it. Of course if you have enough seed, this is fine, because you can test just a few of the batch. If you have a rare species, anything you can do to avoid losing a single seed is a good thing.

Isle Kranner from the Royal Botanic Gardens Kew’s Millenium Seed Bank and Gerald Kastberger from the University of Graz in Austria found that subtle changes in temperature reflect the health of the seed embryo. (They’ve apparently published their results online in the Proceedings of the National Academy of Sciences, but I couldn’t track down the paper today – my information comes mostly from a media release on EurekAlert!)

The seeds are watered and the temperature changes measured using an infrared camera. Water causes sugar inside the seed to dissolve and the seed cools down by about 2 or 3 degrees C. The important discovery was that the cooler temperature was maintained for longer by healthy seeds because they begin breaking down storage starch into sugars. If found to be alive and well, the tested seed can be re-dried and stored again.

Sometimes there is a delay in sugar generation and cooling as the seed goes through a repair phase, particularly in older seeds. So I gather it’s important to collect data on a particular plant or kind of seed to use this technique. So far work has focused on seeds from the garden pea, wheat and rape.

The test takes less than two hours, compared to the current best method which involves germinating the seed and watching…for up to three days.

This new technique will be a time as well as seed saver. In the NSW Seedbank at Mount Annan Botanic Garden we have nearly 10,000 collections of seed – including 38% of the State’s 6,000 or so ‘vascular’ plants and 30% of its threatened species.

To make sure each of these collections is still useful is close to a full-time job for one of our seedbank staff. We expect many of these seeds to last for a few hundred years but we have to keep checking on their health.

In case you are wondering, the oldest viable seeds known were probably from lotus in a now-dry lake bed in China. 466 year-old seeds germinated and grew to mature plants, albeit a little weakly. Older seeds – some thought to be 1200 years old – germinated but died soon after.

Stories circulate about much older seeds springing back to life but seem to be unfounded. 2,000 year-old Date Palm seeds germinated but I don’t think they survived very long. 10,000 year-old lupin seeds discovered in Arctic lemming burrows looked good but wouldn’t germinate. Seeds found in Egyptian tombs I understand are always carbonised and non-viable.

Seeds do have a life expectancy, and that varies from species to species, and from a few days to a few hundred years it seems. For the relatively long-lived, we still need to test their viability so that we can be sure they remain useful for species or habitat restoration. In time we may have to germinate the banked seed to produce the next generation of seed. The more viable seed we can store, the better.

Images: At the top, Director of the Millenium Seed Bank, Paul Smith, Seed Technology Officer at the NSW Seedbank, Leahwyn Seed, and me with one of the 10,000 collections in the NSW Seedbank (photo: Simone Cottrell). Above, Seed Research Officer Amelia Martyn examining seed in the NSW Seedbank (photo: Jaime Plaza).