BOULDER – University of Colorado researchers are studying the effects of light pulses on the growth and nutrition retention of plants to be consumed by astronauts during space flight.

Specifically, the research group is using different methodologies to grow plants rapidly and trigger the retention of certain carotenoids, specifically zeaxanthin, which are important to protect human vision from the exposure of low-level radiation during long-duration manned spaceflight missions.

According to a NASA research study, one of the main problems for astronauts traveling on long-duration space flight is the exposure to ionizing radiation and the consequent oxidative stress, which can harm the retina.

Gioia Massa, a project scientist in International Space Station ground processing and research with the NASA Kennedy Space Center, said that NASA has been looking for ways to produce nutrient-rich vegetables in space, safe for astronaut consumption.

"A space diet has certain things in the prepackaged diet, but might be low or deficient in certain nutrients," she said. "The farther away you get from Earth, the more DNA-level damage there is. There are potentially some plant-based beneficial compounds that could help or prevent this. It's a really promising area for study."

Massa said that NASA is looking to implement a vegetable production system on the next space resupply mission in the near future.

"If plants are grown under certain conditions, they might be able to express more phytochemicals and get higher levels of nutrients, which can help keep the crew healthy," she said.

Compounds absorbed by the human body, such as zeaxanthin, can help prevent biological damage to eyes during spaceflight.

Zeaxanthin, which is known to promote eye health, could be ingested as a supplement, but there is evidence that humans are better at absorbing carotenoids from whole foods, such as green leafy vegetables. The human body cannot produce zeaxanthin on its own.

The CU team included undergraduate researcher Elizabeth Lombardi, postdoctoral researcher Christopher Cohu, and ecology and evolutionary biology professors William Adams and Barbara Demmig-Adams.

With the study idea conceived by Lombardi, the team set out to determine the best way to simulate plant growth while also retaining high amounts of carotenoids.

Current studies of space gardening tend to focus on rapid plant growth, producing large plants as fast as possible while providing optimal light, water and fertilizer. Although this process can yield larger plants, the nutritional value may be depleted because of hurried growth and synthetic climate conditions.

"There is a trade-off," Demmig-Adams said in a statement. "When we pamper plants in the field, they produce a lot of biomass but they aren't very nutritious. If they have to fend for themselves – if they have to defend themselves against pathogens or if there's a little bit of physical stress in the environment – plants make defense compounds that help them survive. And those are the antioxidants that we need."

Using two lines of species of the Arabidopsis thaliana plant, the research team altered conditions to mimic different climates. They found that manipulating growth conditions to cooler temperatures and high light triggered a greater amount of zeaxanthin, but with smaller plants. The optimal growth condition proved to be that of low-growth light supplemented with several short daily light pulses of higher intensity. This triggered zeaxanthin retention without disrupting plant growth.

Zeaxanthin is produced by plants when their leaves are exposed to more sunlight than they can use or absorb, often initiated when the plants are stressed. Limited water availability may hinder the plant's ability to use all the sunlight it's exposed to for photosynthesis. To prevent plant damage, it produces zeaxanthin that protects the plant from excess light and prevents damage. The compound acts similarly with the human eye.

"Our eyes are like a leaf; they are both about collecting light," Demmig-Adams said. "We need the same protection to keep us safe from intense light."

Results of the study could be used for plant production on Earth as well, including research of plant-based human nutrition and urban food production. Additionally, findings could spur an investigation to manipulate plants to express stronger or weaker genetic traits.

Funded by the National Science Foundation and the CU-Boulder Undergraduate Research Opportunities Program, the study was published in October in the journal Acta Astronautica.