【Technological frontier】

　　On December 4th, rice and Arabidopsis seeds, which experienced a 120-day full life cycle in space, returned smoothly with the Shenzhou 14 spacecraft.

This means that my country has successfully carried out the whole life cycle cultivation experiment of rice from seed to seed for the first time in the world.

According to reports, the scientific name of this study is "Molecular Mechanism of Flowering Regulation of Higher Plants under Microgravity Conditions", which was undertaken by the team of Zheng Huiqiong, Center for Excellence in Molecular Plant Science, Chinese Academy of Sciences.

So, why this experiment?

What are the gains?

Why rice and Arabidopsis are being sent to space

　　Zheng Huiqiong introduced that rice is the main food crop for human beings, feeding nearly half of the world's population, and it is also the main candidate food crop for the life support system of manned deep space exploration in the future.

Rice breeding using space microgravity is one of the important directions of space botany research.

"Seeds are not only the food for human beings, but also the carrier for the reproduction of the next generation of plants. To survive in space for a long time, human beings must ensure that plants can complete the alternation of generations in space and successfully reproduce seeds. However, only Arabidopsis thaliana has been completed in space before. , Rapeseed, pea and wheat from seed to seed, while rice, the main food crop, has not been able to complete the whole life cycle cultivation in space before.”

　　The model plant Arabidopsis mainly undertakes the research on the "flowering" part.

Zheng Huiqiong said: "Flowering is a prerequisite for seed formation. We used the model plant Arabidopsis to systematically study the effect of space microgravity on plant flowering."

What happened to rice and Arabidopsis on their space journey

　　Zheng Huiqiong introduced that the on-orbit experiment started with the injection of nutrient solution on July 29, 2022, and ended on November 25, completing the cultivation experiments of the whole life cycle of Arabidopsis and rice seed germination, seedling growth, flowering and seeding.

During the period, the astronauts carried out three sample collections in orbit - rice samples were collected at the booting stage on September 21, samples were collected at the flowering stage of Arabidopsis thaliana on October 12, and samples were collected at the maturity stage of rice and Arabidopsis seeds on November 25.

After collection, samples at the flowering or booting stage were stored in a low-temperature storage cabinet at -80°C, and samples at the seed maturity stage were stored in a low-temperature storage cabinet at 4°C.

　　Zheng Huiqiong said that this time, three space experiments were mainly completed.

First, the cultivation experiment of the whole life cycle of rice from seed germination, seedling growth, earing and seed setting was completed on-orbit, and the images were obtained for analysis.

Second, the space ratooning rice was successfully cultivated after the pruning was completed and matured seeds (second stubble) were formed.

Third, the image observation and analysis of Arabidopsis seed germination, seedling growth, and flowering key genes regulated by three different biological clocks in response to space microgravity were completed on-orbit, and samples were collected on-orbit.

　　Today, the samples have been transferred to the Center for Excellence in Molecular Plant Sciences of the Chinese Academy of Sciences in Shanghai for further testing and analysis.

What are the preliminary findings of the experiment

　　By analyzing images acquired in space and comparing them with those on the ground, it was found that microgravity in space has effects on various agronomic traits of rice, including plant height, tiller number, growth rate, water regulation, light response, flowering time, seed development process and Influencing many aspects such as seed setting rate.

Scientists have made some preliminary findings:

　　First, it was found that the plant type of rice became looser in space, mainly because the angle between stem and leaf became larger; dwarf rice became shorter, and the height of tall rice was not significantly affected.

In addition, the spiral upward movement of rice leaf growth controlled by the circadian clock is more prominent in space.

　　Secondly, the flowering time of the rice space was slightly earlier than that of the ground, but the filling time was extended by more than 10 days, and most of the glumes could not be closed.

Zheng Huiqiong said: "Both flowering time and glume closure are important agronomic traits of rice. Both of them play an important role in ensuring sufficient reproductive growth of plants to obtain high-yield and high-quality seeds. This process is regulated by gene expression and will be used later. Samples for further analysis."

　　Thirdly, experiment with ratooning rice in space and obtain seeds of ratooning rice.

Zheng Huiqiong said: "Two ears of rice can be regenerated 20 days after cutting the plant, which shows that the regeneration of rice in a closed environment with a small space is feasible, which provides new ideas and experimental evidence for the efficient production of space crops. This technology can It greatly increases the yield of rice per unit volume, and it is also the first regenerative rice technology tried in space in the world."

　　Finally, for the first time, the key genes involved in the regulation of photoperiodic flowering by the spatial circadian clock were studied.

Using gene mutation and transgenic methods, three kinds of Arabidopsis with different flowering times were constructed, namely: early flowering, delayed flowering and normal flowering (wild type).

Zheng Huiqiong introduced that through the observation and analysis of the growth and development map of Arabidopsis thaliana in space, it was found that the response of key flowering genes to microgravity is significantly different from that on the ground. greatly extended.

"In addition, after the mutation of the circadian clock gene, the hypocotyl of Arabidopsis thaliana was over-elongated, indicating that the expression of the circadian clock gene is very important for maintaining the normal shape of Arabidopsis thaliana in space and adapting to the space environment. The adaptation of plants to the space microgravity environment provides a new direction. The follow-up research team will further use the returned materials to further analyze the molecular basis of Arabidopsis adaptation to the space environment."

　　(Reporter Qi Fang and Yan Weiqi) (Source: Guangming Daily)