In the film The Martian, Matt Damon’s character survives being stranded on another planet by growing potatoes in his own faeces. And if we want to visit or maybe even settle on other planets for real, we’ll have to find a way to grow plants outside the safe environment of the Earth. On long space voyages in particular, plants will provide a vital source of food and oxygen.
That’s why Tim Peake, the UK astronaut who recently returned from the International Space Station, spent some of his time in space working on an experiment to study plants. And it turns out that a single molecule that also plays a big role in making sure plants grow on Earth, could be key to understanding how to make interstellar greenhouses successful.
Plants have actually been grown in space for a long time. In 1982, Soviet cosmonauts on board the Salyut 7 space station nurtured some thale cress, Arabidopsis thaliana, making it the first plant to produce flower and seed in space. Since then scientists have developed special growth chambers to grow vegetables and fruits in space with the right temperature and atmosphere. The problem is that plants don’t grow as well in space as on Earth, and the reason seems to be the effects of growing them in almost zero gravity.
Zero gravity. Andrey Armyagov/Shutterstock
Growing With Gravity
Plants are able to use the pull of the Earth’s gravity to know which way is down and grow their root in that direction and send their shoot in the opposite direction (an ability known as gravitropism). One way they do this is by using special gravity-sensing cells that contain starch-packed compartments called amyloplasts. Due to the high amount of starch in these amyloplasts, they are heavier than the rest of the cells so they sink to the bottom.
In the weightlessness of space, the amyloplasts do not sink so plants lose some of their ability to perceive gravity. However, that’s not the only way they work out which way is up or down. Earth experiments have shown that even plants with starchless amyloplasts, which don’t allow them to detect gravity, can still display good levels of gravitropism. Similarly in microgravity, plants can detect light (phototropism) and water (hydrotropism) to work out where to grow.