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Apomixis is a type of asexual reproduction in flowering plants, producing identical offspring to the mother plant. Facultative apomixis occurs part of the time, allowing for new strains through sexual reproduction. Arctic plants benefit from apomixis due to harsh conditions. Genetically manipulating apomictic plants for agricultural use is difficult due to polyploidy. Apomixis allows for small farmers to produce their own seeds of elite cultivars. There are two forms of apomixis: gametophytic and sporophytic.
Apomixis is a term commonly used with flowering plants to mean that they have reproduced asexually through seeds. The plants that grow from these seeds are identical to the mother plant. This is of great use for seed production and plant breeding. Over 400 plant species produce apomictic seeds, including dandelions and blackberries.
Facultative apomixis means the situation where apomixis occurs part of the time, but sexual reproduction can still take place. This can be very advantageous from an evolutionary point of view. For example, Kentucky bluegrass periodically produces new strains through sexual reproduction. The best of these are propagated via apomixis and the plant has many strains that are well adapted to localized regions.
Arctic plants benefit greatly from apomictic reproduction. The extreme conditions make pollination by insects difficult, so it is difficult to transfer genetic material from one plant to another. Given the harsh conditions, plants might benefit from having a few more highly specialized strains than the ever-changing populations that would occur with sexual reproduction.
There is much interest in learning how to genetically manipulate apomictic plants for agricultural purposes. There are, however, technical difficulties in doing this. Apomictic plants often exhibit polyploidy, meaning they have more than two copies of their chromosomes. This can make gene transfer difficult.
An advantage of using apomictic seeds would be that small farmers would be able to produce their own seeds of elite cultivars. Viral diseases can be spread through vegetatively propagated plants and this could be minimized by cloning with seed cultures. One could also exploit locally adapted varieties that are resistant to extreme climatic conditions or pathogens.
There are two main forms of apomixis. The first involves the gametophyte, which is the haploid reproductive multicellular structure of the plant. Being haploid means that it contains only one set of chromosomes. The gametophyte produces gametes – mature reproductive cells that would normally unite with another of the opposite sex to undergo sexual reproduction. In gametophytic apomixis, however, an unfertilized egg cell gives rise to an embryo. This is similar to parthenogenesis in animals, which is reproduction in females, without sex.
The second form is known as sporophyte apomixis. In this case, the embryos are formed like buds directly from the integument tissue. This is part of the internal tissue of the egg, the structure that holds the embryo sac. The embryo sac continues with its development, while the sporophyte embryo will go on to form apomictic seeds. This process is also known as adventitious embryo. Except as commonly occurring in citrus plants, sporophyte apomixis is a rare process in higher plants.
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