Botanists find a cool way to preserve an endangered plant’s seeds

If you wonder how cool cool is, it’s at least -196 ℃ (-320 ℉).

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Juglans cinerea is the butternut or white walnut. You’d typically find it in the eastern United States, but it’s getting harder to find. That’s thanks to Ophiognomonia clavigignenti-juglandacearum, a fungus that causes butternut canker, a fatal disease for the tree. Now butternut is endangered. Botanists are gathering seeds to help preserve the plant, but this hasn’t been a huge success because the seeds are difficult to conserve with the usual methods. Now Martin Williams and colleagues have published a new method with a 76% survival rate after seven years. The seeds are cryopreserved.

Cryopreservation means storing the seeds in liquid nitrogen, which boils at -196 ℃. The team used seeds from trees in an ex-situ conservation project in New Brunswick, Canada. The team pulled seeds that had been stored for zero, two and seven years to see how well they germinated.

Top left, a pair of test tubes with axes in them, then a pair of test tubes with germinated seedlings showing a strong stem and radicle. Top-right. a black tray of seedlings. Bottom-left, a tray of considerably bushier seedlings and finally Bottom-right, the seedlings sit in individual pots.
Germination and plantlet growth development of Juglans cinerea embryogenic axes after 7 years of cryopreservation. (A) – embryogenic axis after inoculation in WPM medium, (B) – embryogenic axis with visible root pushing off seed coat after 5 days post inoculation, (C) – embryogenic axes showing different levels of root and shoot elongation after 4 weeks post inoculation, (D) – embryogenic axes transfer from culture tube to soil, (E) – plantlet growth after 8 weeks post inoculation, (F) – final transfer to single pots showing fully acclimatized plants. Source: Williams et al. 2023.

They found a remarkable number of the seeds germinated, around three-quarters. Also, they discovered there was no obvious decline in the seeds after storage in liquid nitrogen, but the authors point out there are limits to this study. They write: “[W]e did not find any significant viability loss due to cryostorage after 7 years, but we do acknowledge that this is only based on one seed lot. However, the high viability of all the seed lots after 7 years post-LN is encouraging and points to minimal loss due to cryostorage conditions.”

“Although seven years is not considered very long when compared to orthodox seed sources that can be kept for 20+ years, it is better than the current storage duration for the species and validates the efforts done in safeguarding butternut through cryopreservation.” 

READ THE ARTICLE

Williams, M., Brophy, M. and van der Meer, B.M. (2023) “Cryogenic storage increases the longevity of butternut (Juglans cinerea, L.) seed embryogenic axes,” Cryobiology. Available at: https://doi.org/10.1016/j.cryobiol.2023.01.002.

Alun Salt

Alun (he/him) is the Producer for Botany One. It's his job to keep the server running. He's not a botanist, but started running into them on a regular basis while working on writing modules for an Interdisciplinary Science course and, later, helping teach mathematics to Biologists. His degrees are in archaeology and ancient history.

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