During lockdown, I decided to rewatch one of my favorite science fiction series: Futurama. The series revolves around Fry, a young man who falls into a “cooling tank” or some kind of freezer tank during the first episode. In this way, he ends up a thousand years in the future where he faces the craziest adventures. While watching, I realized that we do the same thing in our lab. We also make things travel in time.
Time travel as a method of conservation?
A few months ago I was bringing some sweet potato plants to check out. It did this with a new cryopreservation protocol that we developed. We cut off large growth shoots 1 mm from the plant and treat them with an antifreeze solution. Then we immerse the growing shoots in liquid nitrogen, the temperature of which is very low – -196 ° C, after which their flight begins. It may seem a little strange to call this time travel. If tomorrow I check whether our plants are still in the liquid, they will of course still be there, just as if they were in a “very cold” refrigerator. However, there is a fundamental difference between freezing and cryopreservation.
The photo below: From these three pieces of sweet potatoes we cut out the apical (upper) growth points, which we treat with an antifreeze solution. In miniature you can see the cut growth bud (meristem). The plant can be fully grown from this large 1 mm cube sprout. Photographs by Hannes Willems and Natalia Vanega Seliziak.
When frozen, the water in the cell forms ice crystals. You can think of these crystals as needles that puncture frozen cells. Drying may be a way to remove this “harmful” water, and unfortunately there is only a select group of plant seeds (orthodox seeds) that can survive almost complete dehydration. This is why with cryopreservation we only replace part of the water with an antifreeze solution and have to prevent the residual water from forming in a different way.
We do this by immersing the growth bud in a very cold bath of liquid nitrogen. Due to the rapid decrease in temperature, all water molecules stop moving immediately before crystal formation. This state is called a vitreous state and is the core of many cryopreservation protocols. The disadvantage of this technique is that plant tissues larger than 1 mm in size do not cool quickly enough to reach this state and will still form ice crystals. But a large growth bud of 1 mm3 does not suffer from this.
The second difference is aging. The next time you take something out of the refrigerator, pay attention to the expiration date. This date is not a sales scam so replace the contents of your freezer in time. Frozen foods expire because reactions still occur at -20°C. This is where time travel comes in, with cryopreservation the temperature becomes too low for any biological or chemical activity to occur. This means that once the plant is cooled to -196°C, nothing happens to the plant and the sense of time is lost. If the plant was able to blink during the process, it would appear to the plant as if it had suddenly appeared in the future, while hundreds or thousands of years had passed for its tank guards.
We can send plants into the future, but what can we do with that now? The plants I help send into the future help humanity in the future. We keep refrigeration for thousands of different individuals of species that interest us such as bananas, sweet potatoes and cassavas; That people eat billions of pieces every year. We create some kind of backup library. In the future, when a plant dies or someone needs a particular plant, we can take the growth bud out of the time capsule and grow it into a big plant and help solve the problem.
This might seem like a lot of work, because you can keep their seeds, right? This is largely true, there are naturally dried seeds (conventional seeds) and you can freeze or refrigerate them. When they are frozen, they still age, of course, only with the time of cryopreservation remains. But there are also many plants in which seeds cannot be stored.
In our lab we focus on those species. For example, there are plants that do not form seeds, such as bananas and seedless grapes. or plants that produce drought- or cold-sensitive seeds (unconventional seeds). Or crops that reproduce offspring: just think of apples, potatoes, or strawberries, all of which don’t reproduce by seed. If we use the seed there, we may lose the special qualities that the mother plant has.
Traveling to the future on your own?
The main question is, can you save yourself a cryopreservation and look into the future? Unfortunately, this will remain science fiction for a while. We as humans do not have the ability to regenerate to form ourselves again from a small growth bud. This means that we must treat the whole body and here it hangs. To avoid the above ice crystals, we replace part of the water with antifreeze, after which we cool to -196 ° C in a few seconds. But with such a huge body, the inside will cool more slowly, resulting in ice crystals that unfortunately affect all your organs. However, there is one bright spot, “Science can send all of your offspring in the form of eggs and sperm cells into the future. That way, a small part of yourself can still wake up in the future.”
Banes, b. (2019). Sixty Years of Cryopreservation: From freezing sturdy berry branches to creating reference crop groups for future generations. Acta Hortic. 1234, 1-8 https://doi.org/10.17660/ActaHortic.2019.1234.1
Wilms, H., Fanega Sleziak, N., Van der Auweraer, M. et al. (2020) Development of a rapid and user-friendly freezing protocol for sweet potato genetic resources. Sci Rep 10, 14674 (2020). https://doi.org/10.1038/s41598-020-70869-3