Tissue Cryopreservation for Plant Conservation: Potential and Challenges

Cryopreservation of nonseed plant tissues can provide a method for preserving plant genetic diversity ex situ when seeds or spores cannot be adapted to traditional methods of preservation. Shoot tips, somatic embryos, and gametophytes can be used as propagules for long-term storage in liquid nitrogen. Tissue cryopreservation is particularly important in dealing with “exceptional species,” i.e., species that have unbankable seeds or that are producing few or no seeds. In vitro methods can be applied to collecting tissues and establishing cultures as a source of tissue for cryopreservation. The applicability of vitrification/dehydration cryoprocedures has been demonstrated for a wide range of species and types of tissues, and the choice and modifications of methods can be informed by the natural adaptations of the species. While tissues in culture are clonally propagated, preserving tissues from multiple genotypes can provide genetic diversity to a cryopreserved collection. Such collections will ultimately serve to provide materials for restoration if wild populations are lost or severely threatened. There is great potential for the use of in vitro methods and cryopreservation in plant conservation strategies, but there are also both scientific and practical challenges to their application. Whereas in vitro propagation and preservation methods are well established, these methods remain highly empirical in their application to new species. This can be a challenge for conservation, which deals with rare and often unstudied species, which may also have unusual natural adaptations. Because of the labor involved, tissue cryopreservation is also more costly than more traditional ex situ conservation methods, which can limit its use in traditionally underfunded work with endangered plants. However, it is suggested that collaborative efforts can help meet these challenges, bringing together expertise and infrastructure from several sources to facilitate the application of tissue cryopreservation to the ex situ conservation of endangered exceptional species.