The plant germplasm resource bank refers to a preservation facility that protects plant germplasm resources. By 1996, more than 1,300 plant germplasm repositories had been built in the world, and more than 30 crop germplasm repositories had been built in China. The storage type of germplasm is also transferred from a single seed form to various forms such as vegetative organs, cells and tissues, and even DNA fragments. Protected species also extend from sexually propagated plants to vegetatively propagated plants and recalcitrant seed plants. Therefore, the newly established National Germplasm Bank of India and the expanded National Germplasm Bank of the United States in recent years are all integrated storage facilities, including cryogenic storage, in vitro seedling storage, and cryogenic storage. Although the IBPGR (International Board for Plant Genetic Resources) has recommended the design guidelines for the germplasm resource bank, the construction of the germplasm resource bank is a systematic project involving multiple disciplines. At present, there is no specification for the design and construction of germplasm resources in China. The inventory of partially established germplasm resources is causing some problems. For example, the environmental parameters of the storage cold storage cannot meet the design requirements; the insulation layer does not form a closed whole, and a “cold bridge†occurs; the storage cold storage floor below 0° C. does not adopt anti-freezing measures, the ground frost heaves, cracks, etc., resulting in operational efficiency. Not high, some may not even work. At present, there are quite a few articles discussing the introduction of commercial cold storage technology, and there are few reports devoted to the design and construction of plant germplasm resources. With the preservation of plant germplasm resources becoming more and more important in China, some units are preparing to establish a plant germplasm resource bank as a basic platform for resource collection, preservation and utilization. To this end, it is necessary to give an overview of the types and characteristics of plant germplasm resources, design principles and technical parameters, as well as construction experience, which has important guiding significance for the construction of China's plant germplasm resource bank.
Types and characteristics of germplasm resources Germplasm is all living organisms that carry genetic material. For plants, they include not only seeds, but also plants, roots, stems, germs and cells, and even DNA fragments. According to the different germplasm conservation objects, the germplasm resource bank is divided into low-temperature germplasm storage pools, in vitro vaccine storage and cryopreservation reservoirs, and DNA libraries.
1 Low-temperature Germplasm Bank The national germplasm bank built in 1986 in China and the preservation facility of the National Crop Germplasm Conservation Center built in 2002 belong to this type of germplasm resource bank, and the object to be preserved is the plant that produces normal seeds. Germplasm resources. China has collected 3.34×105 crop germplasm resources and deposited it in the national germplasm bank for long-term preservation, ranking first in the world in terms of storage volume. The low-temperature germplasm resource bank mainly consists of two parts, a cold storage for storing seeds and a processing operation room for seed storage. The cold storage part includes the germplasm storage and the engine room. The cold storage is generally built in a brick-concrete structure, and is constructed from polyurethane laminates. The polyurethane laminate plays a role in insulation and gas separation. Through the cooling and dehumidification unit of the machine room, cold air is sent to the cold storage, and defrosting is performed through the evaporator in the refrigerator, so that the cold storage is in a constant low temperature and low humidity state all year round. The pre-treatment operation room includes a seed receiving room, a cleaning room, a germination room, a drying room, a packing room, a water content measuring room, and the like. The low-temperature germplasm resource bank is further divided into long-term and medium-term libraries. The experts of the International Plant Genetic Resources Institute (IPGRI) recommend a long-term storage temperature of (-18 ± 2) °C and relative humidity (RH)< 65%, Seed Storage Moisture Content: General crops are 5%~7%, soybeans 8%, and shelf life up to 20 years. The medium storage temperature (4 ± 2) °C, relative humidity <65%, storage life of 5 to 10 years (FAO/IPGRI, 1994).
2 Storage of plantlets Each cell of a plant is genetically omnipotent and contains all the genetic information necessary for development. The genebank of in vitro seedlings is based on this principle. By using tissue culture techniques, tissue culture or cell culture methods can be used to preserve germplasm resources. The storage of test-tube seedlings generally consists of three parts: a storage bank, a culture bank, and a tissue culture operation room. The storage bank is used for short-term preservation in vitro and the culture bank is used for expanding tissue culture seedlings. The tissue culture operating room is used for sterilization, detoxification and the like of germplasm materials collected in the field. The wall and surrounding structure of the preservation and culture library needs to be insulated, and the refrigeration and dehumidification unit is used to maintain the constant temperature and humidity inside the library to meet the requirements for germplasm cultivation and preservation. In addition, the requirements for ventilation and ventilation are high, and the inlet air in the warehouse must be sterile. The role of the storage bank is to make the tissue culture seedlings grow slowly to achieve the purpose of short-term preservation. Slow growth refers to changing the external environmental conditions of the growth of the culture, so that the growth of the culture is minimized but does not die, so as to extend the subculture time.
3 cryogenic storage library Ultra-low temperature usually refers to the temperature below -80 °C, mainly liquid nitrogen (-196 °C) and liquid nitrogen vapor. When the biological material is stored at such a low temperature, its physiological metabolic activity is almost stopped, which can reduce or even inhibit the genetic variation of the germplasm, so as to maintain the genetic stability of the biological material. This has played an extremely important role in resolving subcultures of tissue cells and mutations that are accumulated in the natural world, saving and rescuing species, and is recognized as an ideal way for the long-term preservation of clonally propagated germplasm resources. The ultra-low temperature library adopts mature ultra-low temperature preservation technology, and the pre-treated plant isolated materials are placed in a sealed cryopreservation tube with anti-freeze protection agent and placed in liquid nitrogen for long-term storage. The main facilities for cryogenic storage are liquid nitrogen tanks and liquid nitrogen storage tanks. Liquid nitrogen tanks are where deposits are stored for long-term storage. Liquid nitrogen storage tanks store liquid nitrogen sources and can be supplied to liquid nitrogen tanks at any time through connecting pipes. The liquid nitrogen source ensures that the temperature of the liquid nitrogen tank is constantly maintained at -196°C. The room where the liquid nitrogen tank is stored should be ventilated well, and the liquid nitrogen tank should be built outdoors.
4 Genetically engineered materials and DNA libraries The establishment of a genetic engineering material library provides a material basis for bioengineering technology breeding and also provides security for bioengineered products and intermediate materials. The DNA database focuses on the preservation of unique, rare, endangered and wild plant germplasm materials. The preservation of genetic engineering materials mainly adopts deep cryogenic refrigerators, liquid nitrogen, and freeze-drying preservation methods. Other genetically engineered materials such as plasmids, DNA, RNA, proteins, and peptides, because they are biomolecular compounds that do not have a cellular structure, can usually be preserved by lyophilization to achieve good results. Using ethanol as a preservation solution, DNA and RNA can also be stored for a long time under low temperature conditions. The construction of DNA storage can be cryopreserved, freeze-dried at -20°C, and stored in a deep freezer (-80°C). Therefore, genetic engineering materials and DNA preservation libraries must be equipped with liquid nitrogen tanks and ultra-low temperature refrigerators (below -80°C), and a low-temperature freezer at -20°C can be built.
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