Salad seeds that went on a round trip to outer space and back grew at a slightly slower rate and aged faster than those on Earth, scientists have found.
A million rocket seeds (Eruca sativa) amounting to 2kg were sent to the International Space Station (ISS) in 2015 with legendary British astronaut Tim Peake.
Six months later they returned to Earth and were grown and monitored by 600,000 children across the UK, in a project overseen by the Royal Horticultural Society.
While seed germination ‘vigor’ was reduced and ageing sensitivity increased, space did not compromise seed viability or the development of normal seedlings.
The researchers believe the only slight changes observed give further hope for a future where humans can grow food in low gravity on another planet.
ESA astronaut Tim Peake poses with packets of rocket seeds for a school Rocket Science project with RHS Campaign for School Gardening, on the International Space Station, December 28, 2015
‘Transporting high quality seeds to space and beyond will be crucial for growing plants that support human exploration of space, Mars and other worlds,’ said Dr Jake Chandler at the Royal Holloway University of London’s department of biological sciences, and lead author of the study in the journal Life.
‘Our study found that a six month journey to space reduced the vigour of rocket seeds compared to those that stayed on Earth, indicating that spaceflight accelerated the ageing process.’
Environmental factors that could potentially affect seeds in space include microgravity, radiation such as galactic cosmic rays and solar energetic particles, a lack of oxygen, low humidity, extreme temperature fluctuations and mechanical vibrations.
In particular, rocket seed ageing during the experiment was caused mainly by exposure to low-level ionizing radiation from galactic cosmic rays, trapped protons, and solar energetic particles.
Major Peake was representing the European Space Agency (ESA), which confirmed radiation was the most likely culprit for space seeds, which were sealed in foil bags, growing less effectively.
Germination at Brixington Primary School, Devon. More than 8,600 schools and groups in the UK, making up around 600,000 young people, were involved with the project to sow the rocket seeds
‘Radiation is the biggest risk for dormant seeds stored for a long time in the space environment because cosmic rays are so energetic,’ said Jason Hatton, head of biology and environmental monitoring at the European Space Agency (ESA).
‘When they impact the ISS there is a showering effect and they fragment further and become even more energetic.
‘Nuclei and some protons can penetrate the ISS and interact with any biological material on board.
‘They either pass through the seed, or deposit energy there. They can fragment further once inside the seed too, which leads to greater damage.’
Seed germination was scored over time as either rupture of the testa (seed coating) endosperm (tissue inside the seed), or visible protrusion of the radicle, the plant embryo that develops into the primary root and signifies end of germination.
A higher percentage of the Earth seed samples reached these stages faster than the samples that were stored on the ISS, data shows.
Effect of spaceflight on germination of Eruca sativa (rocket) seeds. (A) The Space seed batch was stored on the ISS for six months, sealed at low humidity in foil bags. (B) Visible stages of rocket seed germination. (C) Time course analysis of testa rupture and endosperm rupture of Earth seeds compared to Space seeds. (D) Thermal time modeling of Earth-WS (warehouse stock) seed germination over a range of temperatures
The absorbed radiation dose on board the ISS was 100 times more than on the Earth’s surface, and affected the seed transcriptome, germination physiology and ageing sensitivity.
However, the radiation exposure during missions to Mars would be at least five times greater than that of the ISS, and to maintain the quality of dormant seeds during spaceflights, they will need extra protection.
‘While we should carefully consider protecting seeds from potentially harmful factors including space radiation and mechanical vibration, the seeds remained alive, and the prospect of eating home-grown salad on Mars may be one small step closer,’ said Dr Chandler said.
More than 8,600 schools and groups in the UK, making up around 600,000 young people, were involved with the project to sow the rocket seeds.
They were given the mission to grow the seeds once they returned alongside a nearly identical packet of seeds that had remained on Earth.
Tim Peake called it one of the ‘largest and most inspirational experiments of its kind’, showing how more than half a million schoolchildren can contribute by collecting scientific data.
The prospect of eating home-grown salad on Mars may be one small step closer, researchers say, after only slight degradation in the growth of seeds that spent six months in space. Soil on Mars actually does have the nutrients plants would need to survive on the red Planet, NASA says
‘When humans travel to Mars, they will need to find ways to feed themselves, and this research helps us understand some of the biology of seed storage and germination which will be vital for future space missions.’
In March, NASA reported that lettuces grown aboard the ISS had more nutritional value than the same type of lettuce being grown on Earth.
NASA says it was served by astronauts with oil and vinegar dressing and the space leaves were a wild success, described as ‘awesome’ by the crew who ate them.
It was not revealed by the Royal Holloway researchers whether the new ISS-grown rocket developed its distinctive peppery flavour as well as the Earth-grown version.
NASA, which is planning to send humans to Mars by the 2030s, claims that Martian soil contains essential nutrients plants need to survive, meaning crops could be grown there.
‘In reality, the soil on Mars actually have the nutrients plants would need to survive on Mars,’ NASA said.
‘There may not be the right amount of nutrients depending on where astronauts land on the Red Planet, so fertilisers may need to be added to the soil.’
Major Peake, who became Britain’s first official astronaut in December 2015 when he spent six months on board the ISS, will be conducting a virtual Q&A session on Monday about the rocket experiment.
Last year at the UK Space Conference in Newport, Peake, who plans to return to the ISS in the next five years, said a human will land on Mars within the next 50 years.
‘In the next 50 years we will be celebrating humans on Mars. I am quite sure of that.
‘I would be cautious about saying we will be celebrating humans on Mars in the next 20 years.’