Basic aspects of the <em>in vitro</em> conservation of plant germoplasm

The in vitro conservation constitutes essential part of the general strategy for the conservation and the exchange of genetics resources in the entire world. It offers the possibility to store a great number and variety of samples in a reduced area. It guarantees the sanity of the samples and it increases the exchange of plant materials. Two conservation methods in vitro exist, whose use varies in dependence of the duration that requires the storage; the method of minimum growth is used with more frequency to conserve a little time, while, the cryopreservation guarantees the in vitro conservation for long periods of time. In particular, the cryopreservation has been applied in many species for the conservation of pollen, meristems, apexes, zygotic embryos, somatic embryos and cellular suspensions. Two groups of techniques in the cryopreservation are recognized: the classic techniques based on the partial chemical dehydration and the programmed freezing and the new techniques based on the vitrification that consist on the change from the liquid state to a vitreous denominated intermediate state and that it avoids the formation of glasses of ice responsible for the mechanical damage to the cellular membranes during the freezing. It is known that the membranes of the vegetable cells can be damaged by the action of different biophysical and biochemical factors and they need a special chemical protection during the cycle of freezing-unfreezing with treatments cryoprotectors with substances of a heterogeneous group of compounds that have great affinity for the water and that to certain concentrations they are not toxic. Some basic aspects of plant germplasm in vitro conservation and the main results decribed by the national and international scientific community about in vitro conservation of different plant species are sumarized in this research.Key words: cryopreservation, dehydration, minimum growth, vitrification