Mosses may appear simple, but they’re far from fragile. They thrive in some of the harshest places on Earth — Antarctica, arid deserts, high mountain peaks and more.
“We’ve long wondered about the molecular mechanisms that allow moss to endure such extreme conditions,” says Tomomichi Fujita, a plant physiologist at Hokkaido University in Japan.
Fujita and his colleagues may now have part of the answer. They grew spreading earthmoss (Physcomitrium patens) for nearly eight weeks under artificial gravity up to 10 times stronger than that of Earth. Surprisingly, the intense gravity boosted chloroplast size, shoot growth and photosynthesis rates, the researchers report July 16 in Science Advances.
The finding is impressive, possibly representing the tip of iceberg of plants’ adaptability to gravity, says Jun Yang, a plant geneticist at Shanghai Chenshan Botanical Garden. Usually photosynthesis rates drop under high stress; in a 2014 study, a team of researchers from Savitribai Phule Pune University in India found that it plummeted in wheat grown at 500 times Earth’s gravity.
That past result makes sense, Fujita says. “When we have a fever, we don’t want to walk. We just want to lay down. That’s true for the plant. If they are exposed to stress conditions, they also stop growing.”
Fujita was curious about what would happen to photosynthesis under less severe gravity. His team started with clumps of moss 2 millimeters long and grew them for eight weeks in a custom-built centrifuge chamber designed for long-term hypergravity experiments. The device spun continuously, creating three, six and then 10 times Earth’s gravity.
A small chamber monitored how quickly CO₂ was absorbed by the moss — an efficient way to estimate the rate of photosynthesis. When grown at six and 10 times Earth’s gravity, the spreading earthmoss showed a 36 to 52 percent increase in photosynthesis compared with normal gravity. (On Earth, earthmoss can metabolize 6 to 8 micromoles of CO₂ per square meter of plant surface area each second.) The plants had greater CO₂ diffusion and larger chloroplasts than those under Earth’s normal gravity.
The researchers also identified a gene that was critical in the growth of the chloroplasts. They called it Issunboshi1 or IBSH1, after a tiny but powerful boy from Japanese folklore. Turning up the gene’s activity under normal gravity mimicked the effects of hypergravity, enlarging chloroplasts from about 4–6 micrometers to 7–11 micrometers and boosting photosynthesis by up to 70 percent.
The findings suggest plants could already have tools for adapting to new gravitational environments, a potential clue suggesting how moss ancestors might have migrated from water to land long ago. The results could help researchers discover similar genes in other plants and potentially tweak them to boost productivity, the team says.
The finding is fascinating, but puzzling, says Hideyuki Takahashi, a plant physiologist at Chiba University in Japan, who has conducted multiple space flight experiments in microgravity with several plant species. “Why does this happen under six and 10 times [Earth’s gravity]?” he asks. “Plants have never experienced such gravity in the history of [their] evolution.”
Microgravity experiments at the International Space Station might offer some clues. Fujita’s team has already carried out the experiments and is working to publish the results soon.