Cryopreservation of Agronomic Plant Germplasm Using Vitrification-Based Methods: An Overview of Selected Case Studies

Abstract

Numerous environmental and endogenous factors affect the level of genetic diversity in natural populations. Genetic variability is the cornerstone of evolution and adaptation of species. However, currently, more and more plant species and local varieties (landraces) are on the brink of extinction due to anthropopression and climate change. Their preservation is imperative for the sake of future breeding programs. Gene banks have been created worldwide to conserve different plant species of cultural and economic importance. Many of them apply cryopreservation, a conservation method in which ultra-low temperatures (−135 °C to −196 °C) are used for long-term storage of tissue samples, with little risk of variation occurrence. Cells can be successfully cryopreserved in liquid nitrogen (LN) when the adverse effect of ice crystal formation and growth is mitigated by the removal of water and the formation of the so-called biological glass (vitrification). This state can be achieved in several ways. The involvement of key cold-regulated genes and proteins in the acquisition of cold tolerance in plant tissues may additionally improve the survival of LN-stored explants. The present review explains the importance of cryostorage in agronomy and presents an overview of the recent works accomplished with this strategy. The most widely used cryopreservation techniques, classic and modern cryoprotective agents, and some protocols applied in crops are considered to understand which parameters provide the establishment of high quality and broadly applicable cryopreservation. Attention is also focused on the issues of genetic integrity and functional genomics in plant cryobiology.

Cryopreservation of Hazelnut (Corylus avellana L.) Axillary Buds from In Vitro Shoots Using the Droplet Vitrification Method

“…Defining the suitable exposure duration of explants to the vitrification solutions is essential for cell dehydration, necessary to avoid the formation of intracellular ice crystals during freezing and thawing, and to prevent injury by chemical toxicity of cryoprotectants [56,57] or excessive osmotic stress [30]. In the current study, cryopreservation by DV was applied to axillary buds of C. avellana, the Italian cultivated variety Tonda Gentile Romana, collected from in vitro grown shoots.…”

Cryopreservation of Endangered Ornamental Plants and Fruit Crops from Tropical and Subtropical Regions

“…Many of those endangered species are fruit and ornamental plants. Several environmental and endogenous factors alter the level of plant biodiversity in natural populations, which is the basis of evolution and adaptation [ 1 ]. The rapid development of proper approaches for the long-term preservation of genetic resources seems to be necessary.…”

“…Various types of explants can be cryopreserved, including mature seeds, apical or axillary shoot tips, embryogenic cultures, pollen, zygotic and somatic embryos, embryonic axes, shoot primordia, roots, protocorms, protocorm-like bodies (PLBs), cell suspensions, callus, protoplasts, spores, bulblets, tiny leaf square-bearing adventitious buds (SLS-BABs), stem disc-bearing adventitious buds (SD-BABs), microtubers induced from nodal segments, rhizome buds, dormant buds, plumules, and in vitro derived explants [ 1 , 15 ]. Among them, shoot tips are used most often with tropical and subtropical fruit and ornamental species.…”

Vitrification Solutions for Plant Cryopreservation: Modification and Properties

“…Cryopreservation through the application of vitrification solutions was first reported in plant cells [13][14][15]. Currently, the vitrification-based methods that use vitrification solutions are considered the most widely applied for plant cryo-biologists [16,17]. There are more than 800 papers on shoot tip cryopreservation using vitrification solutions in the literature [18,19].…”