Ex situ conservation of plants means protecting plant species away from their natural habitat. The main methods are seed banks, botanic gardens and tissue culture.Seed banks store large numbers of seeds for long periods. The Millennium Seed Bank at Wakehurst, run by the Royal Botanic Gardens, Kew, holds seeds from tens of thousands of species. The method is:
1. Seeds are collected from wild plants, cleaned and checked.
2. They are dried to a low water content, so ice crystals do not form and damage the cells.
3. They are sealed and stored at about −20 °C, which slows metabolism so they stay alive for decades.
4. Samples are germinated regularly to test their viability. If viability falls, plants are grown to produce fresh seed.Botanic gardens grow living collections of rare plants, carry out research, educate the public and supply plants for reintroduction. They can produce many genetically identical plants from a few cells by micropropagation (tissue culture), which is useful for species that produce few seeds.Advantages of seed banks: many seeds take up little space, storage is cheap, seeds from many individuals preserve genetic diversity, and seeds can be used to restore damaged habitats.Disadvantages: some seeds, such as those of oak and avocado, are recalcitrant and die if dried or frozen. Collected seeds only represent the genetic diversity of the plants sampled. Stored seeds are not exposed to natural selection, so they do not evolve and may be poorly suited to the climate when they are eventually replanted.
1. Seeds are collected from wild plants, cleaned and checked.
2. They are dried to a low water content, so ice crystals do not form and damage the cells.
3. They are sealed and stored at about −20 °C, which slows metabolism so they stay alive for decades.
4. Samples are germinated regularly to test their viability. If viability falls, plants are grown to produce fresh seed.Botanic gardens grow living collections of rare plants, carry out research, educate the public and supply plants for reintroduction. They can produce many genetically identical plants from a few cells by micropropagation (tissue culture), which is useful for species that produce few seeds.Advantages of seed banks: many seeds take up little space, storage is cheap, seeds from many individuals preserve genetic diversity, and seeds can be used to restore damaged habitats.Disadvantages: some seeds, such as those of oak and avocado, are recalcitrant and die if dried or frozen. Collected seeds only represent the genetic diversity of the plants sampled. Stored seeds are not exposed to natural selection, so they do not evolve and may be poorly suited to the climate when they are eventually replanted.