Seed specialists ensure the survival of a key component of life and provide a secure environment for possible revival,Yi Ling and Yue Ranran report in Kunming.

For some,life is put on pause at the very beginning. In the basement of a four-story building in Kunming's northern suburbs,hundreds of thousands of precious plant seeds are carefully stored at — 20 C. This Germplasm Bank of Wild Species,located in Yunnan's provincial capital in Southwest China,is the largest facility of its kind in Asia.

It houses more than 94,000 plant seed accessions from around 11,000 wild species,representing over one-third of China's wild seed plants.

The seeds are carefully stored in specially designed glass bottles,which are lined up on rows of shelves in a concrete warehouse 30 meters underground.

According to Cai Jie,head of the seed bank's germplasm collection center,Chinese researchers discovered ancient lotus fruit in the peat layer of a dried-up pond in Pulandian,Northeast China's Liaoning province,in 1952.

Lab tests determined that the fruit had been buried for 1,288 years. Surprisingly,the seeds inside the fruit successfully germinated and grew into beautiful flowers after their tough outer shells were ground away.

"This magical discovery had a profound impact on my career,"Cai says.

"Seeds are natural time capsules,carrying the genetic code of plants. They can revive at the right moment. We preserve seeds with great care because we need to have reverence for nature and believe in the power of life."

The germplasm bank project,founded in 2007 and run by the Chinese Academy of Sciences'Kunming Institute of Botany,includes a seed bank,a plant tissue bank,a DNA bank,a microbial bank,an animal germplasm resource bank and other sectors.

Dubbed the"Noah's Ark"of plants in China,it is a leading research and preservation facility for the germplasm of rare and endangered plants in Asia,serving as a refuge for wild plants.

"When a species faces extinction,we can use preserved germplasm resources to revive it,"Cai says.

"I really hope such a day never arrives."

Despite its incredibly rich biodiversity,China is facing a grim situation in wild plant conservation. Research has revealed that among the country's higher plants (a genus of plants with tissues that conduct water and minerals),at least 4,000 species are threatened,constituting 10 percent of the total,according to Cai.

Since the genes of most plants are contained in their seeds,germplasm resources have become crucial carriers of the genetic information. Chinese scientists have been actively collecting seeds from endangered or rare wild plant species and storing them in seed banks.

Challenging process

However,it's challenging for a seed to qualify for inclusion in the germplasm bank due to strict entry standards. Seeds must first meet the"3E"criteria — they must be endangered,endemic and economically significant.

The term"endemic"not only refers to species unique to China but also those exclusive to specific regions. Based on these criteria,nationally and provincially rare and endangered plants,such as the Himalayan yew and Yunnan maple,are given priority for preservation.

In addition to meeting the"3E"criteria,the seeds must undergo over 70 procedures,with the most crucial being the three stages of collection,examination and storage,Cai says.

Recalling an unforgettable experience in the Guangxi Zhuang autonomous region in southern China,Cai describes the seed collection process as meticulous and full of surprises.

"When we pruned branches from a fruit-laden tree,we instinctively used our bare hands to catch them. However,we quickly realized this was a bad idea as a sharp,stinging pain shot down from the back of our hands to our arms and then straight to our hearts,"Cai recalls.

"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."

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 humans.

Cai says 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 would 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.

Ideally,they try to collect 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 seeds available in the original population to avoid jeopardizing regeneration.

To better protect these rare seeds and assist in future ecological restoration,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 use and ecological restoration,"Cai says.

The 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 storage time,low temperature and dry conditions are used to prolong the seed's life span.

"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,"says Qin Shaofa,a seed curation supervisor at the germplasm bank.

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 only extract a portion of the seeds for weighing,calculate the average weight,and determine the number of seeds by weighing the total,"Qin explains.

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 C 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 — 20 C.

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

New technology

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

Clad in a full-body protective suit to endure the frigid conditions of liquid nitrogen,Lin carefully extracts embryos from magnolia tree seeds stored in a cryopreservation tank. The embryos are then tested to determine if they will successfully grow upon thawing.

Cryo-biotechnology is the combination of ultralow temperature preservation technology and a regeneration system. It plays an important role in the long-term conservation of endangered plants,important crops and their wild relatives,Lin says.

"Many wild plants possess genes that aid their survival in challenging environments,rendering them resistant to diseases and drought. In the future,we might need these genetic materials to breed new crops that can better adapt to the changing climate,"he adds.

However,the seeds do not remain in hibernation indefinitely."Every five or 10 years,we break the seed dormancy,take a small sample,and conduct germination experiments to assess their viability,"says Yang Juan,a seed germination supervisor.

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

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

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

As to future plans,Cai says they will advance international cooperation on seed collection and duplication.

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

（China Daily 2024年7月6日）

来源：https://www.chinadaily.com.cn/a/202407/06/WS668896eea31095c51c50cb86_5.html