◎ Reporter for Science and Technology Daily Lu Chengkuan
Can rice seeds germinate, grow, bloom, and produce seeds in space? Our space science experiment gives the answer.
On December 4, the re-entry module of the Shenzhou 14 manned spacecraft successfully landed at the Dongfeng landing field. On the same day, rice and Arabidopsis seeds returned with the capsule were delivered to the Space Applications System along with other space science experiment samples.
The astronauts collected samples three times in orbit
Seeds are not only human food, but also the carrier of breeding the next generation of plants. In order to survive in space for a long time, it is necessary to ensure that plants can complete generation alternation in space and successfully reproduce seeds.
However, only Arabidopsis, oilseed rape, pea and wheat have been cultivated from seed to seed in space, while rice, a major food crop, has not been cultivated in space for its full life cycle.
"For the first time in the world, we have completed a full-life 'seed to seed' space culture experiment of rice. At the same time, flowering is a prerequisite for seed production, and we have systematically studied the effects of spatial microgravity on plant flowering using the model plant Arabidopsis thaliana." Chinese Academy of Sciences molecular plant Science Center of Excellence in innovation researcher Zheng Huiqiong told reporters.
In the life science program of the Chinese Space Station, the research team led by Zheng Huiqiong undertook the project "Molecular Mechanism of higher plant flowering regulation under microgravity".
According to Zheng Huiqiong, from July 29, 2022 to November 25, 2022, the "Molecular Mechanism of Higher Plant Flowering Regulation under Microgravity" project carried out a total of 120 days of in-orbit experiments, and completed the cultivation experiments of seed germination, seedling growth, flowering and seed setting of Arabidopsis and rice.
During that time, the astronauts collected three samples in orbit, including rice samples at the booting stage on September 21, samples at the flowering stage of Arabidopsis thaliana on October 12, and samples at the seed maturity stage of rice and Arabidopsis thaliana on November 25. After collection, samples at flowering or booting stage were stored in a low-temperature storage cabinet at -80℃, and samples at seed maturity stage were stored in a low-temperature storage cabinet at 4℃. On December 4, the samples returned to Earth with the Shenzhou XIV. According to the plan, after the handover in Beijing, the samples will be transferred to the Shanghai laboratory for further testing and analysis.
Zheng said that the space project completed the cultivation experiment of rice from seed germination, seedling growth, heading and seed setting in orbit and successfully obtained relevant images. The space regrowth rice was cultivated successfully and the mature seeds were produced, i.e., two stubble seeds. The responses of Arabidopsis seed germination, seedling growth and flowering key genes regulated by three different biological clocks to space microgravity were observed and analyzed, and samples were collected in orbit.
Spatial microgravity affects many agronomic characters of rice
"By analyzing spatially acquired images and comparing them with ground-based controls, we found the effects of spatial microgravity on a variety of agronomic traits in rice, including plant height, tillering number, growth rate, water regulation, response to light, flowering time, seed development process and seed setting rate." Zheng Huiqiong said.
The in-orbit experiment showed that the plant type of rice became more loose in space, the dwarf rice became shorter, and the height of the tall rice was not significantly affected. In addition, the spiraling motion of rice leaf growth controlled by biological clock is more prominent in space.
"The flowering time of rice in space is slightly earlier than that in ground, but the filling time is extended by more than 10 days, and most of the glumes cannot be closed." Zheng Huiqiong said that flowering time and glume closure are both important agronomic traits of rice, which play an important role in ensuring adequate reproductive growth of plants and obtaining high-yield and high-quality seeds. This process is regulated by gene expression, and we will use the returned samples for further analysis.
At the same time, the project also carried out the space experiment of regrowing rice and obtained the seeds of regrowing rice. "Two rice ears were regenerated after 20 days of cutting, indicating that regrowing rice in a confined environment with a narrow space is feasible. This provides new ideas and experimental evidence for efficient production of space crops." Zheng Huiqiong said the technology can greatly increase the rice yield per unit volume, and is the first regrowing rice technology tried in space in the world.
In addition, the project is the first to investigate key genes involved in the regulation of photoperiodic flowering by the space clock. Using genetic mutations and genetic modification, the researchers created three varieties of Arabidopsis thaliana with different flowering times: early flowering, late flowering, and normal flowering (wild type).
By observing and analyzing the spatial map of the growth and development of Arabidopsis thaliana, the researchers found that the response of key flowering genes to microgravity was significantly different from that on the ground. Among them, Arabidopsis thaliana, which blooms early on the ground, also has a longer flowering time under space microgravity conditions.
"After the mutation of the circadian clock gene, the hypocotyl of Arabidopsis thaliana was overextended, indicating that the expression of the circadian clock gene is very important for maintaining the normal morphology of Arabidopsis thaliana growth in space and adapting to the space environment. This provides a new direction for the future use of modified flowering genes to promote the adaptation of plants to the space microgravity environment." Zheng Huiqiong said that the team will further use the returned materials to further analyze the molecular basis of Arabidopsis thaliana's adaptation to the space environment.