Today is International Fascination of Plants Day, so I wanted to share some plant science that I have recently been fascinated by. I've become a bit obsessed with research on growing plants in space, how plants respond to microgravity, and the potential for space agriculture. Plant research in space focuses on growing plants for long-term space flight, where the plants can not only feed the astronauts but also scrub the air of carbon dioxide, produce oxygen, and recycle water. The exchange of nutrients and wastes between plants and astronauts can form the cornerstone of a bioregenerative life support system (BLSS) for orbiting space stations and perhaps even future space colonies.

Figure from "Seeds in Space" by Mary Musgrave, Seed Science Research, 2002.

Plants have travelled to space since some of the earliest orbital missions, and experiments on how seeds sprout and grow in space have been used to study how plants move in response to light, water, and oxygen without the confounding variable of how plants respond to gravity. While plants can be grown from seeds inside specially designed growth chambers in space and seeds flown in orbit can grow when brought back to Earth (like the moon trees that orbited the moon during the Apollo 14 mission), it took nearly 40 years of research before plants grown in space could form fertile seeds and reproduce to create self-sustaining agriculture.

Microgravity affects plants in many ways, changing how water diffuses through the soil to the roots and travels up the stems, and importantly, changing how air moves around the plant and how gasses like oxygen and carbon dioxide are exchanged. The composition of the cabin air onboard the spacecraft as well as ventilation around the plant to promote air exchange have to be very precisely controlled in order to allow for reproduction on board. Even after conditions were optimized and plants could produce fertile seeds, the peculiarities of microgravity can affect the metabolism of the plant, often limiting the plant robustness and nutritional properties.

Figure from Tuominen et. al. "Plant secondary metabolism in altered gravity."

Adapted from a figure from "Seeds in Space" by Mary Musgrave

The alteration of airflow as well as changes in plant metabolism in space can have an effect on other plant characteristics as well, including their scent. The "Overnight Scentsation," a miniature breed of rose, was sent into orbit on the 1998 Space Shuttle Discovery mission STS-95 to identify the smell of the flower in space. John Glenn, the first American to orbit the Earth also became the oldest person to fly in space during this mission, where he performed headspace analysis to capture the scent of the space rose. The overall aroma was pleasant but much reduced compared to the smell of the rose grown on Earth. Analyzing the components of the rose volatiles showed that while the smell was decreased overall, the production of the main rose-smell constituents, phenyl ethyl alcohol, citronellol, geraniol, and methyl geranate actually increased in space. This ultra-rosey space rose smell was resynthesized based on the headspace trace, and is a primary note in the Shiseido fragrance Zen [PDF].

Plants in space can tell us about the potential for life in orbit and homesteading on the final frontier, but also about the amazing biology and chemistry of plants that make life possible on Earth. I'm fascinated by the moon tree and the space rose, as well as the motion of growing plant roots uncontrolled by the pull of gravity. Plants are fascinating, on Earth and in space.