Finnish Forest Research Institute  Metla

Media release 4.11.2005

Vitrification successfully used for the first time in cryopreservation of silver birch

Cryopreservation is a modern technique used for the conservation of forest genetic resources. No expensive equipment or programming of slow cooling is needed, because vitrification is based on cryoprotective chemical treatment of samples. The method has now been used successfully for the first time with silver birch (Betula pendula Roth). According to a study performed at Metla, vitrification was not found to affect the genetic fidelity of birch.

Vitrification, just like traditional cryopreservation, refers to immersion of samples in liquid nitrogen at -196°C. For birch, vitrification is applicable for cryopreservation of tissue cultured material.

In order to keep the cells alive during vitrification, it is essential that the formation of ice crystals within the cells is prevented. In traditional cryopreservation methods, cells are dehydrated, which causes extracellular crystallization during the slow cooling process from 4°C to -38°C.

When samples – in this case, axillary buds - were processed with vitrification, they survived the transition from 4°C directly to liquid nitrogen. The highly concentrated solutions of cryoprotective agents used in vitrification prevent the crystallization of ice in the extracellular domain and both intra- and extracellular liquids remain vitreous during the freezing and cryostorage.

When the results were studied at the molecular level, no signs of genetic effects were observed when DNA-markers of the birch plants regenerated after vitrification were compared to their donor trees. Vitrification is an equally efficient cryopreservation method as the traditional cryopreservation: the average recovery of the studied samples was 71%. As for equipment requirements, vitrification facilitates cryopreservation of silver birch even in smaller tissue culture laboratories.

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