"Water becomes really sticky on the space station," notes Gilroy, adding that "if you water your plants, the water wants to stick to the surface of the plants and to the roots, creating a low-oxygen environment."
The long-term goal of these studies is to understand how plants grow in space so that one day astronauts could benefit from their own lab-grown crops, both as a food supply and for air purifying purposes, Gilroy explained back in 2012.
"The only life support system we know that works really, really well is the Earth's, and that is built around plants and microbes," he said in a statement prior to a similar experiment that he was preparing for at the time.
"It's not 100 percent clear it will work, but the long-term goal is to integrate those tools into space missions: plants to grow your food and purify the air and water; microbes as the waste-processing system," Gilroy clarified in that statement.
For this purpose, his team has chosen a small mustard plant called Arabidopsis, commonly known as mouse-eared cress, and which Gilroy has dubbed "the lab rat of plant biology."
To start off his fourth zero gravity experiment, Gilroy shipped hundreds of Arabidopsis seeds in SpaceX's latest Dragon cargo delivery to the ISS. These seeds belong to a mutant version of Arabidopsis, which can withstand stressful low-oxygen environments, mentions the news release.
According to Spaceflight Now, the results of this experiment could offer more insight into how plants might grow in future habitats on the moon or on Mars.
Unlike the previous Arabidopsis experiments that were performed in the dark, the Expedition 54 crew — which has just been completed today (December 19) with the arrival of three new astronauts — will be growing the seeds under light, in order to provide "more realistic conditions." To make this possible, the astronauts will be employing the "Veggie" plant growth system, successfully used in 2015 by the Expedition 44 crew to grow lettuce aboard the ISS.
The astronauts will also use microscopes to take images of the living plants in their various growth stages. This has never been done before, notes the university news release, and will considerably add to the knowledge of zero-gravity plant growth.
In addition, Gilroy's team has genetically engineered a type of fluorescent Arabidopsis that produces luminescent proteins when deprived of oxygen. The Expedition 54 crew will be imaging these fluorescent plants in orbit midway through the experiment, in order to piece together "a map of where within the plant there is local low-oxygen stress," Gilroy points out.
Once the experiment is completed, the astronauts will freeze the Arabidopsis plants and prepare them for their return home trip aboard the same Dragon capsule that brought them to the ISS. To stop the plants from growing any further until their journey back to Earth, the astronauts will apply a chemical fixative after one month of zero-gravity growth.
While Expedition 54 will be carrying out this experiment, Gilroy will also be growing identical Arabidopsis seedlings in his lab. This way, when the zero-gravity samples are returned to the university, he will be able to compare them and assess the plants' "growth with and without gravity," details the news release.
The goal is to see "how well the plants grow" in space, as Gilroy puts it. Previous zero gravity experiments have shown that plants develop well enough in space to "go through an entire life cycle," he points out. But Gilroy's aim is to find out how the process can be improved.
"We are still at the level of working out whether the issues in space are intrinsic to the biology, or whether we're just not really good space gardeners yet."