Plants in Space

The plants. The careful planning. The speed. The stars. The silence. The growth.

Plants with roots leading to NC State took a journey that most don’t have the opportunity to take. On June 3, 2021, plant biology experiments prepared by NC State professor Marcela Rojas-Pierce and research professor Imara Perera were shot into space at more than 17,600 miles per hour while aboard SpaceX’s Dragon spacecraft. After the treacherous journey, the spacecraft latched onto the International Space Station, and the onboard astronaut crew carried out the protocols that the researchers developed for plant research. 

These studies are being conducted to help us better understand how to prepare for future longer missions to the moon and even possibly Mars, while also learning how to improve agriculture practices here on Earth. Plants would be integral to these missions not only for nutrition but also for mental health. 

Which crops can you grow in space?

Right now, crops are being grown on the ISS only at a small scale, with a focus on those that are nutrient-rich and can be harvested quickly, such as salad crops. There’s still a lot we need to learn before growing them more widely due to the harsh, unnatural conditions the plants face in space.

“The astronauts have shown that you can grow peppers, you can grow lettuce and you can grow flowers, but they’re not perfect,” says Marcela Rojas-Pierce. “They don’t give you the same number of seeds or the same quality of seeds because they’re responding to a very different environment. It’s not just microgravity, but it’s also radiation, gas exchange, and all of that.”

Can plants grow without gravity?

Even though there are a lot of questions still to be answered, researchers do know that plants can grow in space by depending on other instinctive behaviors.

“What we and so many others are finding broadly is that although plants sense up and down by gravitropic mechanisms, roots also go towards wherever the water is and shoots often also just go towards wherever the light is,” says Perera. “However, the roots are not quite as straight [without gravity]. They’re a little more wavy and wiggly.”

Rojas-Pierce’s and Perara’s labs are focused on understanding how gravity affects their model organism from the mustard family, Arabidopsis thaliana, also known as the thale cress. What they’re learning about the thale cress can also be applied to other plants on a larger scale.

How does gravity affect plant organelles?

The Rojas-Pierce lab is focused on how microgravity affects vacuoles, plant cells’ largest internal structures. Vacuoles have many important functions, including storage and helping the plants with turgor pressure, which is the force within the cell that pushes the plasma membrane against the cell wall.

Organelles are separated from the rest of the cytoplasm by a membrane. Membranes can fuse with each other if two organelles are of the same type and they’re close enough together. Vacuoles can fuse, too. This is an important part of cell growth because vacuoles occupy most of the volume of the cell. If there is a decrease or inhibition of vacuole fusion, it could be one of the many reasons why a cell would grow slower.

To study this, Rojas-Pierce sent two Arabidopsis genotypes to the ISS: one wild type and one mutated. The mutated genotype lacks proteins that help vacuole fusion, resulting in smaller vacuoles in the plant.

“We’re investigating whether there are detectable differences in vacuole fusion in the mutant and in the wild type when we compare plants that are grown in microgravity versus plants that are grown in the ground in controlled conditions,” says Rojas-Pierce.

It took the lab group years and a few trips to the Kennedy Space Center to make sure the experimental protocol was space-ready. The protocol proves that it’s possible to do a chemical treatment of live cells on the ISS, preserve the samples and complete data analysis after the samples come back. 

After the plants returned from space, the Rojas-Pierce group started data analysis. The lab has detected significant differences in vacuole fusion in some cell types under microgravity, but the changes are subtle and complex. 

How does gravity affect plants’ genes? 

Perera is studying how microgravity alters metabolic pathways. Her lab has sent several projects to space, most recently on SpaceX-22 and SpaceX-24, which launched in December 2021. The continued missions over the past decade have allowed her research projects to advance as technology advances. 

In the SpaceX-22 and SpaceX-24 missions, they’re focusing on the development and testing of new hardware she and Eric Land —a postdoctoral researcher in her lab— helped develop called the Multi-Variable Platform (MVP). The MVP acts as a horticultural system in space for small plants. It has two centrifuges that can spin anywhere from zero gravity up to two times gravity on Earth. 

“What we’re hoping to do is not just get it to where it can run our experiment well, but we’ve been trying to set this up in such a way that we can fill the needs of all the plant community that have these burning questions,” says Land. 

To understand how microgravity affects plant metabolic pathways, the Perera lab is working to identify which plant genes are responding differently to an environment with microgravity, such as in space. The researchers are also looking at plants’ proteins. 

Perera has found several genes that respond in a dose-dependent fashion to gravity. Some genes turn on with more gravity, others turn off with more gravity, and others act more like a switch where it’s one mode or the other. She looks forward to comparing these findings with the findings in her most recent space study. 

What’s Next? 

Besides learning more about how plants grow under microgravity, it’s also essential to determine the best method for water and nutrient delivery while in space. Because the traditional soil and watering methods aren’t possible in space, scientists and engineers are investigating other methods of delivering nutrients and water to plants in a way that’s more efficient, including growing solutions and watering systems. 

However, each step scientists and engineers take in understanding the best growth opportunities for plants in space is a step closer to growing plants—and crops—more widely in space. 

“By looking at how the plants are adapting to this unfamiliar environment, it will help us maybe come up with ways to grow a healthy and happy future for crop production in space,” says Perera.