BEIJING, June 17 (Xinhua) -- At China's space station orbiting 400 kilometers above the Earth, the Shenzhou-23 astronauts are conducting a rice cultivation experiment designed to last two seed-to-seed cycles. Inside an experimental module about the size of a microwave oven, rice seeds have already germinated, and seedlings are developing.
The purpose of this experiment is to explore the genetic stability and regenerative capacity of rice in a microgravity environment, according to a recent report by China Science Daily.
This trial represents a critical step toward establishing in situ food production technology for extraterrestrial environments, laying the foundation for sustainable grain production in future deep-space exploration missions, including those on the Moon and Mars.
REPRODUCTION UNDER MICROGRAVITY
All life on Earth has evolved under the planet's surface gravity, with structures, metabolism, and genetic regulatory mechanisms all adapted to this gravitational environment.
As humanity attempts to venture beyond Earth's cradle into deep space, a fundamental scientific question arises: Can plants complete their entire life cycle from seed germination, seedling growth, and flowering to reproduction under microgravity conditions?
Scientists view this as the key to determining whether humans can achieve in situ plant cultivation and establish stable food supplies in space.
The research team conducting this experiment comes from the Center for Excellence in Molecular Plant Sciences, Chinese Academy of Sciences. Team leader Zheng Huiqiong said that as early as 2002, the team explored "space cell fusion," a critical step in biological reproduction, during the seven-day Shenzhou-4 mission.
In 2006, the "Shijian-8" satellite mission conducted experiments on plant flowering and pollination.
"Through real-time microscopic imaging, we observed that, unlike pollen on Earth, where it completes pollination under gravity, in space it floats in the air, with only a small amount landing on the stigma," Zheng explained. "This means that if cross-pollinating crops are grown in space in the future, artificial-assisted pollination will be necessary."
The team then turned to self-pollinating plants. Research conducted aboard the "Tiangong-2" space laboratory, launched in 2016, focused on controlling flowering time in self-pollinating plants, including Arabidopsis and rice. The study confirmed that microgravity delays the expression and transport of flowering genes, causing plants to bloom later in space.
In 2022, using the Wentian lab module of China's Space Station, the team completed, for the first time, the full life-cycle cultivation of rice "from seed to seed," successfully harvesting space-grown rice seeds. These seeds were brought back to Earth and bred for three generations, demonstrating good reproductive capacity.
Zheng recalled they found that seeds returned from space had a very poor sense of direction. "They would lie flat during germination instead of growing straight upward. This shows that microgravity leaves a profound imprint on plants, what we might call 'space syndrome.'"
TWO CULTIVATION CYCLES
The first challenge their current research faces is the extremely limited space. The experimental module's height is only 20 centimeters, which imposes an extreme challenge on plant architecture control. To address this, the team selected early-maturing, compact and dwarf rice varieties.
These varieties are highly adaptable and have a growth cycle of three to four months, matching the crew rotation period so that the experiment can continue from the Shenzhou-23 to the Shenzhou-24 mission.
In addition, water and gas management is highly demanding. In the microgravity environment, water droplets secreted by rice leaves do not naturally roll off as they would on Earth; instead, they float within the module. If not promptly collected, the rice plants could drown in their own exuded water. Maintaining a dynamic balance in air composition is also very difficult because the module is tightly sealed.
Furthermore, the microgravity environment presents unprecedented challenges during sowing. If seeds are simply scattered onto soil, they will not only fail to land, but soil particles will also float away, making it impossible to achieve close contact between seeds and soil.
To address this challenge, the team developed a plug-in fixed-planting device. It is a fixing device with small plates. After astronauts harvest the first-generation seeds, they can attach rice spikelets to the plates with biological glue and simply insert the plates into the soil during sowing, efficiently and reliably fixing the seeds in place.
The team prepared two types of special rice seeds. One consists of seeds that have never left Earth. The other consists of offspring from space-harvested seeds that were brought back to Earth in 2022 and bred for three generations.
Through this control setup, the team hopes to verify their hypothesis that if plants possess some form of memory, then the offspring of these space seeds may exhibit greater environmental adaptability.
Based on these two types of seeds, the experiment conducted parallel comparisons using two different reproduction modes across four units. The first group used sexual reproduction. When the first-generation rice matures, the spikelets will be cut and fixed with the plug-in device, then placed in new cultivation units, allowing the rice to reproduce the next generation via seeds in space.
The second group used asexual reproduction. Inspired by ratoon rice technology from ground-based agriculture, only the root system will be retained after the rice matures. By using the remaining root stubble, new shoots could regenerate and grow into a new crop.
With experimental groups advancing in parallel, scientists will not only be able to observe the performance of seeds with different origins but also directly compare which method, sexual or asexual reproduction, holds greater advantages in the space environment, thereby providing direct evidence for selecting future space agriculture production models. ■
