Recalling his unforgettable experience in south China's Guangxi Zhuang Autonomous Region, Cai described the seed collection process as meticulous and full of surprises.

"When we cut off the branches full of fruit, we instinctively used our bare hands to catch them. However, we quickly realized it was a bad idea as a sharp, stinging pain shot down from the back of our hand to our arm and then straight to the heart," Cao said.

"We washed our hands with soap and water, and even tried using urine, but none of these methods relieved the pain. It wasn't until a few days later, when the plant's toxicity had diminished, that the stinging finally subsided," Cai added.

It was later discovered that this plant Boehmeria nivea is a member of the nettle family, and has spines on its fruit containing a toxic substance that induces severe pain in the human body.

Cai said that such "painful" encounters are part of their job, but each seed collection experience is "precious." "I often think that if we missed saving one species, it could face extinction. What a tremendous loss that would be."

To ensure genetic diversity, researchers gather seeds from various locations where the same plant species grows.

It is ideal to collect over 10,000 mature and plump seeds per sample, or a minimum of 2,500 seeds. However, it is crucial to ensure that the collection does not exceed 20 percent of the available seeds in the original population to avoid jeopardizing the plant's regeneration.

To better protect these rare seeds and assist in future ecological restoration, the researchers record detailed information such as collection time, location, altitude, soil type and surrounding environment. They also preserve the plants' twigs with leaves, flowers and fruits as herbarium vouchers to create a "DNA ID" for the seeds in the future.

"The 'DNA ID' provides a molecular genetic pedigree for the accurate conservation of species in our country, and lays a solid foundation for future germplasm utilization and ecological restoration," Cai said.

The collected seeds must undergo procedures such as drying, cleaning and counting before they can be stored. Ordinary seeds, such as corn and wheat, can be stored at room temperature for up to two years. To extend the seed's storage time, low temperature and dryness are used to prolong the seed's lifespan.

"Some seeds are incredibly small, like those from certain orchid plants, which are only tens of micrometers in size. Cleaning these seeds presents a significant challenge, not to mention counting them accurately," said Qin Shaofa, a GBOWS seed curation supervisor.

Due to static electricity in the drying room, seeds from orchid plants often stick to weighing instruments, making them difficult to remove.

"To avoid losses, we can only extract a portion of the seeds for weighing, calculate the average weight, and determine the number of seeds by weighing the total weight," Qin explained.

Before counting the seeds, a random sample is taken and examined using an X-ray machine, so scientists can easily see whether the seeds are plump or shriveled.

After examination, the seeds undergo another round of cleaning, quality testing, counting and drying. They are then stored at 15 degrees Celsius with a balanced relative humidity of 15 percent for one month to induce dormancy.

Finally, after being sorted into sealed containers according to size, the seeds enter their "hibernation" stage in cold storage at minus 20 degrees Celsius.

Each species' seeds are divided into two parts: one stored in the basic repository for permanent preservation, and the other in the active repository for germination testing and research purposes, Qin said.

Photo taken on Oct. 20, 2021 shows somatic embryogenesis of cryopreserved embryogenic cells at the Germplasm Bank of Wild Species in Kunming, southwest China's Yunnan Province. (Xinhua/Jiang Wenyao)

NEW TECHNOLOGY FOR PERMANENT PRESERVATION

"At present, we are working on the technology of seed cryopreservation. If successful, seeds will be placed in liquid nitrogen at minus 196 degrees Celsius after special treatment, which may achieve permanent preservation of seeds," said Lin Liang, a senior engineer at the Kunming Institute of Botany.

Cryobiotechnology is the combination of ultra-low temperature preservation technology and a regeneration system.

Clad in a full-body protective suit to shield against the extreme cold of liquid nitrogen, Lin carefully extracted embryos from magnolia tree seeds stored in a cryopreservation tank. The embryos were then tested to determine if they would successfully regrow upon thawing.

Cryobiotechnology plays an important role in the long-term conservation of recalcitrant seeds, endangered plants, important crops and their wild relatives, Lin said.

"Many wild plants have genes that help them to survive in harsh environments and make them disease or drought-resistant. In the future, we might need these genetic materials to breed new crops that can better adapt to the changing climate," he added.

However, the seeds will not remain in hibernation indefinitely. "Every five or ten years, we break the seed dormancy, take a small sample, and conduct germination experiments to assess their viability," said Yang Juan, a GBOWS seed germination supervisor.

Cai underlined the seed bank's direct impact on people's daily lives, highlighting wild rice as a prime example.

The genes of hybrid rice, developed by the late renowned Chinese scientist Yuan Longping, are derived from wild rice. In 1970, Yuan's team discovered male sterile plants of wild rice in China's southernmost province of Hainan. Years later, they successfully bred hybrid rice using these wild rice plants, greatly increasing rice yields in China.

"As the late renowned botanist Wu Zhengyi had said, a species affects a country's economy, and a gene relates to a country's prosperity," Cai said.

Speaking about future plans, Cai said they will advance international cooperation on seed collection and duplication.

"Seeds symbolize life and hope. It's our common responsibility to better protect the future of humanity," Cai said.

（新华社 2024年6月26日）

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