cryopreservation is a technology for preserving cells, tissues and organs in liquid nitrogen (-196℃), which is widely used in the long-term preservation of animal, plant and microbial germplasm resources. Plant cryopreservation is usually combined with in vitro culture technology to achieve long-term safe preservation of pollen, callus, somatic embryos, zygotic embryos, seeds, in vitro meristems and dormant buds. The cryopreservation technology for important crops and ornamental plants is relatively mature, and the world’s major wild species and varieties of potatoes and bananas have achieved cryopreservation.
The genebank is the most effective and economical method for ex situ conservation of wild plants. The seeds of most wild plants can be stored for a long time at low temperature (-20°C) after dehydration, and their life span is greatly extended. The seeds of some plants cannot tolerate dehydration and cannot be stored at low temperatures. They are usually called recalcitrant seeds. According to the review article “Seed banking not an option for many threatened plants” published by the British Millennium Seed Bank in Nature Plants in 2018, 8%of plants worldwide produce recalcitrant seeds, but in critically endangered plants and Among tree species, this proportion is as high as 36%and 33%, respectively. Goal 7 of The Global Strategy for Plant Conservation requires ex situ conservation of 75%of endangered species. The realization of this goal requires investment and support for plant cryopreservation technology.
The volume of water becomes larger after crystallization. The cell moisture will form large crystals at ultra-low temperature, which will destroy the cell membrane structure and cause cell death. The first generation of plant cryopreservation technology induces extracellular crystallization by program cooling (controlled rate cooling) to slowly dehydrate cells, increase the concentration and viscosity of intracellular fluid, and enter vitrification at ultra-low temperature. , To avoid intracellular crystallization and ensure cell survival. The first generation of cryopreservation technology is only suitable for cold hardy plants. The new vitrification ultra-low temperature technology treats cells with a high concentration of plant vitrification solution. At the same time as osmotic dehydration, cryoprotectant enters the cell and changes the thermodynamic properties of the cell liquid. It can achieve intracellular and rapid cooling. The extracellular vitrification keeps the integrity of the cell structure and the ability to regenerate. The new generation of plant cryopreservation technology has realized the preservation of tropical plants, greatly expanding the scope of plant cryopreservation.
The cell membrane is the core part of low temperature injury and osmotic response. During the vitrification cryopreservation process, cells have undergone severe and complex osmosis and temperature changes. The survival and death of cells depends on whether the cell membrane can effectively respond to the above-mentioned stresses. For a long time, the response mechanism of the cell membrane to the ultra-low temperature process has not been resolved, which also restricts the further development of ultra-low temperature technology. Recently, Dr. Lin Liang from the Seed Biology Research Group of Kunming Institute of Botany, Chinese Academy of Sciences, Associate Researcher Chen Hongying, Researcher Hugh W. Pritchard and Researcher Li Weiqi collaborated to use the cryopreservation system of embryonic cells of Magnolia officinalis as a model system. Using lipidomics analysis method, the differences of 12 different ultra-low temperature treatments were compared, and the response mode of cell membrane to the vitrification ultra-low temperature preservation process was revealed. The results showed that the two relative processes of osmotic protection treatment and rehydration treatment occurred in phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylcreatine (PA) and phosphatidylglycerol (PG). The clusters are exchanged and the cell membrane is remodeled. After PVS solution treatment, the total lipid level is significantly increased, which reserves a large amount of lipid molecules for the freezing process that the cells will undergo. The results of this study show that lipid remodeling and prevention of lipid degradation are the keys to the success of the PVS method. From the perspective of membrane lipid molecules, the PVS-based plant cryopreservation mechanism is analyzed, which provides new ideas for improving the vitrification cryopreservation technology and expanding the versatility and application scope of plant cryopreservation. The above research results are titled”Lipid Remodeling Confers Osmotic Stress Tolerance to Embryogenic Cells during Cryopreservation” and published online in the International Journal of Molecular Sciences in the field of biology.
This research work was crossed by the National Natural Science Foundation of China (NSFC 31770375, 31500272), the Yunnan Provincial Applied Basic Research Project (2017AB001), the Joint Fund of Yunnan Local Colleges (2018FH001-029), and the Southwest Wildlife Germplasm Bank of China. Cooperative Team” open research project, funding from the Shandong Agricultural Good Seed Project (Grant No. 2019LZGC01801).
Figure 1. The survival rate of Magnolia officinalis embryonic cells after 12 different ultra-low temperature treatments.
Figure 2. Changes in membrane lipid molecules of Magnolia officinalis embryonic cells after 12 different ultra-low temperature treatments.
Figure 3. Model of changes in membrane lipid molecular composition of Magnolia officinalis embryonic cells during ultra-low temperature.