PROJECT: Seeds in Space
Many things that you see in nature seem to be obvious. But are they? Do you understand how seeds that grow in the darkness of the soil ‘know’ in which direction they should develop a sprout? They probably feel gravity and develop a sprout against the direction of this force. But what about the stage of growth when the sprout emerges from the soil surface? Is the top of the little plant attracted by light, or does gravity continue to be the only reference for the growth direction?
To understand the influence of gravity and light on the growing of seeds, we grow lettuce seeds in two different boxes: with and without light. We take the results of the two same experiments done by ESA astronaut Andre Kuipers on board the International Space Station (ISS) during the Delta mission in 2004.
Read the instructions of the experiment and discuss:
- What are we going to examine? (purpose)
- What do we think will happen? (assumption)
- What are we going to change? What are we not going to change
- How and what will we measure?
- What are we going to do?
- How long will the experiment last?
- Will we repeat the experiment?
- How many measurements are we going to take?
- Prepare two boxes, preferably from plastic since they will become wet inside. Dimensions are about 15 x 5 x 5 cm. One box should be completely dark, the other is identical with a hole of about 1.5 cm diameter.
- Get fast growing seeds. Seeds in Space originally applied Seeds from rocket lettuce.
- In both boxes, cover one large side with a thin layer of paper tissues.
- Distribute the seeds over these tissues; about 20 seeds will do.
- Add some water. A teaspoon is enough.
- Close the boxes and make sure that the one with the hole has this hole facing upwards.
- Switch the light on and let the light shine through the hole.
- Let the experiment run for four days.
- Every 24 hours, open the boxes and note what you see. Measure the length of the plants and note color and growth direction.
- 10. Summarise your results in a table and/or a graph .
1. Discuss to answer the following questions:
– What have we discovered?
– Do we know why this happened?
– Was our assumption correct?
2. Compare your results with the ones obtained by ESA astronaut Andre Kuipers who performed the experiment on board the ISS:
In Space, the box with light shows the seeds grow in the direction of the light. The leaves are green.
In Space, the box with darkness shows the seeds don’t know what to do. They grow in all directions and the leaves are thin and pale yellow.
CREDITS: this experiment was designed by J. Van Loon and this project was carried out with the support of the whole “Seeds in Space” team. It flew during the Delta Mission to the ISS in April 2004 and was performed on board by ESA astronaut Andre Kuipers.
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PROJECT: Seeds in Space Many things that you see in nature seem to be obvious. But are they? Do you understand how seeds that grow in the darkness of the soil ‘know’ in which direction they
Seeds in space – how well can they survive harsh, non-Earth conditions?
Ph.D. Student in Cell and Molecular Biology, University of Arkansas
Gina Riggio is affiliated with Blue Marble Space.
The Conversation UK receives funding from these organisations
Will we someday colonize space? Will our children visit other planets? To achieve goals like these, we’ll need to crack one crucial challenge: how to feed ourselves for long periods away from Earth.
A trip to Mars would take months, and exploring the depths of the galaxy would take even longer. Provision of nutritious food for travelers is a significant obstacle. While stockpiling food is an option, storing enough to last many months strains weight and space limitations in spacecraft – and missions could easily outlast food shelf life. Growing food in space will be essential.
Essential – and not necessarily easy. The conditions in the vacuum of space are quite harsh compared to Earth. Seeds in space must be able to withstand large doses of ultraviolet and cosmic radiation, low pressure and microgravity.
Believe it or not, the first space travelers were seeds. In 1946, NASA launched a V-2 rocket carrying maize seeds to observe how they’d be affected by radiation. Since then, the scientific community has learned a great deal about the effects of the space environment on seed germination, metabolism, genetics, biochemistry and even seed production.
Astrobiologists David Tepfer and Sydney Leach recently investigated how seeds would do back on Earth after spending extended periods on the International Space Station. The experiments they conducted on the EXPOSE missions were much longer than many other ISS seed experiments, and placed the seeds on the outside of the station, in the dead of space, rather than inside. The goal was to understand not only the effects of long-term radiation exposure, but a bit about the molecular mechanisms of those effects.
Seeds have some defenses
Seeds possess a couple of remarkable traits that Tepfer and Leach hypothesized would give these “model space travelers” a fighting chance.
Seeds protect their important insides with a strong external seed coat. LadyofHats
First, they contain multiple copies of important genes – what scientists call redundancy. Genetic redundancy is common in flowering plants, especially food products such as seedless watermelon and strawberries. If one genetic copy is damaged, there’s still another available to do the job.
Secondly, seed coats contain chemicals called flavonoids that act as sunscreens, protecting the seed’s DNA from damage by ultraviolet (UV) light. On Earth, our planet’s atmosphere filters out some harmful UV light before it can reach us. But in space, there is no protective atmosphere.
Would these special features be enough to let the seeds survive or even thrive? To find out, Tepfer and Leach conducted a series of experiments – both outside the International Space Station and back on Earth – with tobacco, Arabidopsis (a flowering plant commonly used in research) and morning glory seeds.
The EXPOSE-R experiment attached to the exterior of the International Space Station. NASA, CC BY
Bombarded with energy
Their EXPOSE-E experiment flew to the International Space Station (ISS) in 2008 and lasted 558 days – so just under two years.
They stored the seeds in a single layer on the outside of the ISS behind a special kind of glass that let in ultraviolet radiation only at wavelengths between 110 and 400 nanometers. DNA readily absorbs UV radiation in this wavelength range. A second, identical set of seeds was on the ISS, but shielded completely from UV radiation. The purpose of this experimental design was to observe the effects of UV radiation separately from other types of radiation like cosmic rays that are everywhere in space.
Tepfer and Leach chose tobacco and Arabidopsis seeds for EXPOSE-E because both have a redundant genome and therefore good odds for survival. They also included a genetically engineered variety of tobacco with an antibiotic resistance gene added; the plan was to later test this gene in bacteria and determine if there was any damage. In addition to normal Arapidopsis, they sent up two genetically modified strains of the plant that contained low and absent UV-protective chemicals in their seed coat. They also sent purified DNA and purified flavonoids. This gave the researchers a wide range of scenarios by which to understand the effects of space on the seeds.
A second ISS mission called EXPOSE-R included only the three types of Arabidopsis seeds. These received a little over double the dose of ultraviolet light because of the longer experiment time, 682 days. Lastly, researchers performed a ground experiment back in the lab that exposed Arabidopsis, tobacco and morning glory seeds to very high doses of UV light for only a month.
After all these various exposure conditions, it was time to see how well the seeds could grow.
The Expose-R experiment was equipped with three trays containing a variety of biological samples – including seeds. NASA, CC BY
What would researchers reap?
When the seeds returned to Earth, the researchers measured their germination rates – that is, how quickly the root emerged from the seed coat.
The seeds that had been shielded in the lab did the best, with more than 90 percent of them germinating. Next came the seeds that had been exposed to UV radiation for one month in the laboratory, with better than 80 percent germinating.
For the space-traveling seeds, more than 60 percent of the shielded seeds germinated. A mere 3 percent of space UV-exposed seeds did.
The 11 Arabidopsis plants that did grow from both the wild type and genetically engineered seeds did not survive once planted in soil. Tobacco plants, however, showed reduced growth but that growth rate recovered in subsequent generations. Tobacco has a much heartier seed coat and a more redundant genome, which may explain its apparent survival advantage.
When the researchers plugged the antibiotic resistance gene into bacteria, they found it was still functional after its trip to space. That finding suggests it’s not genetic damage that’s making these seeds less viable. Tepfer and Leach attributed the reduced germination rate to damage to other molecules in the seed besides DNA – such as proteins. A redundant genome or built-in DNA repair mechanisms weren’t going to overcome that damage, further explaining why the Arabidopsis plants didn’t survive transplanting.
In the ground experiments, the researchers found that radiation damage is dose-dependent – the more radiation the seeds received, the worse their germination rate.
These discoveries could inform future directions for research in space agriculture. Scientists may consider genetically engineering seeds to have added protection for the cellular machinery critical for protein synthesis, such as ribosomes. Future research will also need to explore further how seeds stored in space germinate in microgravity, rather than on Earth.
As researchers add to the knowledge of how space affects plants and their seeds, we can continue to make the strides necessary toward producing food in space. It will be a crucial step toward sustainable colonies that can survive beyond the comfortable confines of Earth’s biosphere.
If you want to live on Mars, you're going to need to grow food. Seeds are naturally equipped to handle challenging Earth environments, but how well can they survive what they'll encounter off-planet?