In the proper conditions, space gardens could benefit from their extraterrestrial setting: The first study examining both radiation and light quality in the context of sprout growth has revealed that certain wavelengths of light can counteract the harmful ionizing radiation found in the cosmos, yielding mung bean sprouts with high levels of antioxidants.
A team of experts in agricultural science, physics and biology at the University of Naples Federico II discovered that red-blue light leads to a higher antioxidant content in sprouts. They also found that red light alone was able to offset the negative effects of X-ray radiation on sprouts at even the highest X-ray doses tested. The researchers detailed their findings in a study that was published May 10 in Acta Astronautica.
Fresh microgreens, which are young vegetable greens harvested immediately following the appearance of leaves, can offer astronauts vital nutrition. They could also help them with certain mental challenges unique to space travel.
"During a long mission, astronauts suffer from isolation. The cultivation of a space garden and the care of plants can help them counteract these negative effects of isolation on psychology," lead author and associate professor Veronica De Micco told The Academic Times.
"Most astronauts have a dream to have a fresh salad and fresh tomatoes in space," De Micco said. But astronauts on short missions or on the International Space Station usually rely on dried, non-perishable food. "If we want to support life in space and if we are looking towards Mars, it is impossible to bring all the resources that humans will need from Earth," she added. Instead of packing food from the home planet, De Micco and her colleagues think that biomass should be grown onboard.
De Micco has been interested in extraterrestrial environments for decades. While on an exchange program in the U.S., she traveled to Cape Canaveral to visit a NASA laboratory. "Twenty years ago, they were one of the laboratories studying the effect of monochromatic light on crop growth," she said.
Radiation comes from both natural sources, such as ultraviolet light produced by the sun, and non-natural sources, such as an X-ray machine. Low-energy forms of radiation, known as non-ionizing radiation, are not immediately harmful to the human body. On the other hand, high-energy or ionizing radiation — such as gamma rays in space — can damage DNA in humans and other animals. "[Ionizing] radiation represents the major risk for manned exploration and colonization of [the space] environment," the co-authors reported in the study.
Curiously, plants are much more resistant than animals to high-energy ionizing radiation. "At low doses that are already lethal for mammals, cosmic radiation can have no effect on plants or can even have positive effects on plant growth," explained De Micco. In the current study, 100% of the mung bean sprouts survived when exposed to ionizing radiation. De Micco and her colleagues wanted to take advantage of plants' resilience and leverage the power of cosmic rays to create a regenerative space garden.
Sprouts are ideal for space cultivation because they are easy to grow and pack a punch of vitamins and flavonoids in a relatively small plant. Flavonoids are edible compounds found in broccoli, berries and many other foods that are known to be nutritious and rich in antioxidants. Mung beans are especially fit for this purpose, as antioxidants in the sprouts can help lower inflammation from radiation stress. This variety is also easy to cultivate and very common — on Earth, that is.
The team in Italy first exposed germinated seeds of mung beans to X-ray radiation and then incubated the growing plants under different wavelengths of light. They focused on X-rays because their effects resemble those of low-energy protons in space. The types of visible light were dark, white, red and red-blue.
The researchers measured the growth of the sprouts for nine days, measuring physical traits such as root length and leaf width at three different intervals. After the full growth cycle, the co-authors used liquid chromatography-mass spectrometry, a common approach in analytical chemistry, to calculate the levels of flavonoids and isoflavones, a specific kind of flavonoid, in the plants. They also used microscopy to analyze cell size and shape.
Nearly all growth traits were influenced by the dose of radiation and light quality. Red-blue light was found to stimulate antioxidant and flavonoid production in the sprouts, while red light apparently offset all the tested levels of X-ray radiation, even at the highest dosage of 20 grays. This result is in line with many previous studies that observed accelerated growth of bean plants and algae under certain wavelengths of light.
Flavonoids are a type of polyphenol, and in the authors' view the possibility of polyphenol-rich food for space exploration is particularly encouraging. "A diet rich in polyphenols is desirable for astronauts engaged in long manned missions, because it helps to counteract the diseases due to chronic ionizing radiation exposure," the co-authors wrote in the paper. "Good nutrition is the base for any healthy astronaut," De Micco added.
The results suggest that plants may be able to support a regenerative, living system in a contained space environment. Indeed, plant species as small as microgreens can filter the air through photosynthesis, converting the carbon dioxide we exhale to the oxygen we need to breathe, said De Micco. Sprouts also have the potential to recycle water in a less glamorous process of purifying astronauts' bodily waste to provide water for plants.
De Micco now works on a project funded by the Italian Space Agency to support life in space. She is studying how ionizing radiation affects the growth of plants, fungi and other types of flora that can be cultivated outside Earth's atmosphere. Her focus is on sprouts, microgreens and tomatoes — three ingredients that can make a simple, but satisfying, salad for astronauts, she noted.
As longtime collaborators, De Micco and co-author Carmen Arena are already planning their next experiment. The researchers will study the relationship between different types of radiation as well as ions, such as carbon ions, and plant growth. De Micco also plans to complete the experiment on germinating seeds, which are more resistant to growth. Germination, she explained, is key for a seed-to-seed life cycle of a plant onboard a spacecraft.
"In the long-duration missions, we will need to look at the production of biomass and the staple crops: cereals, potatoes, wheat and so on," De Micco said. "If we produce food that is rich in antioxidants directly on board and it can be integrated into the astronaut's diet, the defense of the human body to counteract 'space diseases' can be improved."
The study, "Effect of light quality and ionising radiation on morphological and nutraceutical traits of sprouts for astronauts' diet," published May 10 in Acta Astronautica, was authored by V. De Micco, C. Amitrano, P. Vitaglione, R. Ferracane, M. Pugliese and C. Arena, University of Naples Federico II.