Natural sunscreens help morning glory seeds survive doses of ultraviolet (UV) radiation that would burn most humans to a crisp, according to a new study. The hardy seeds of the common flowering plant would probably even survive a voyage between planets, say the researchers. This might help researchers decide which species to send on future missions to Mars, a place that is bombarded with UV light because of its thin atmosphere. It also validates the concept of panspermia, the idea that life might have hopscotched through our solar system—or others—by hitching a ride on asteroids or comets.
“These results add to the fast-growing body of evidence showing that panspermia is not only possible, but absolutely inevitable,” says Chandra Wickramasinghe, director of the Buckingham Centre for Astrobiology at the University of Buckingham in the United Kingdom, who was not involved in the study.
The research began a decade ago, when astronauts placed about 2000 seeds from tobacco plants and a flowering plant known as Arabidopsis thaliana on the outside of the International Space Station. For 558 days, the seeds were exposed to high levels of UV light, cosmic radiation, and extreme temperature fluctuations—conditions that are lethal to most forms of life.
Yet when the seeds returned to Earth in 2009, roughly 20% germinated and grew into normal-looking plants. “Seeds are ideally suited to storing life,” says David Tepfer, an emeritus plant biologist at the Palace of Versailles Research Center of the National Institute for Agronomic Research in France. But scientists are only beginning to understand how the seeds survived. Now, 10 years later, Tepfer and Sydney Leach, an emeritus physicist at Paris-Meudon Observatory in France, have taken a closer look at the DNA of some of these space-traveling seeds.
The scientists focused on seeds that no one had tried to germinate, looking at a short section of genetic code that had been inserted into their genomes before they left Earth. This snippet of code let researchers test the structure and function of space-exposed DNA, and they found DNA degradation on both counts. Tepfer and Leach say that some of the DNA’s structural units might have chemically fused together, a process that inactivates genetic code. Tepfer suspects that seeds damaged by very short wavelength UV light could germinate if they repaired that DNA damage as they grew.
But the scientists wanted to see just how much abuse a seed could withstand. In a follow-on experiment in the laboratory, Tepfer and Leach exposed three types of seeds—morning glory, tobacco, and A. thaliana—to high doses of UV light. Tepfer and Leach thought morning glory seeds might do well based on their large size, tough seed coats, and ability to survive for more than 50 years in soil. They found that only morning glory seeds germinated after being exposed to light roughly 6 million times the dose typically used to sterilize drinking water, conditions that killed the much smaller tobacco and A. thaliana seeds. The team suggests a protective coating containing flavonoids, compounds commonly found in wine and tea that act as natural sunscreens, might be responsible for the seeds’ robustness, they reported in March in Astrobiology. Feeding animals a high-flavonoid diet might confer resistance to UV light and make them better suited for interplanetary travel, Tepfer suggests. “They might become more ultraviolet-resistant,” he says. “Red wine or green tea, anyone?”