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Genome stability in the frozen Cosmos
In discussing conservation of endangered plant species, the media usually concentrate on direct protection of the plant and its habitat, and ignore the detailed laboratory work that forms an essential part of a multi-disciplinary approach. One aspect of laboratory work with endangered species is establishing the best methods for conservation and storage of germplasm. For some species, cryopreservation of plant tissue is an appropriate method for germplasm conservation but it embodies a particular set of problems, including tissue damage during freezing, loss of viability during storage, failures in regeneration from the stored tissue and the occurrence of genetic changes (somaclonal variation) during the organ or tissue culture phases. However, with careful study of all the factors involved, these problems may be overcome, as exemplified by the work on a rare, endangered and interesting composite, Cosmos atrosanguineus (Wilkinson et al., Reading University and Royal Botanic Gardens Kew, pp. 65-74). Optimal procedures for cryopreservation of cultured shoot tips have already been established, and in this paper the authors turn to investigation of the regeneration phase. Many of the cells of the main meristematic dome do not survive freezing and, thus, after return to culture conditions, regeneration of shoots is initiated from particular groups of cells, usually at the base of the primordia, rather than from the main meristem itself. However, success in storage and regeneration would be of much less value if these processes cause genome instability, which is totally undesirable when attempting to preserve endangered species. The authors have thus employed Amplified Fragment Length Polymorphisms (AFLP), a PCR-based procedure, rightly described as the ‘most sensitive multilocus fingerprinting technique . . . available’. So far their results obtained with seven pairs of PCR primers are very encouraging: comparison between original plant stocks and regenerated shoots revealed no sequence differences. For cryopreservation of C. atrosanguineus, genome instability is simply not a problem.
Professor J. A. BryantUniversity of Exeter, UK
j.a.bryant{at}exeter.ac.uk
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