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In Botany, what is Apomixis?
Apomixis is a term commonly used with flowering plants to indicate 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 indicates the situation where apomixis occurs part of the time, but sexual reproduction can still happen. This can be very advantageous evolutionarily. For instance, Kentucky bluegrass periodically produces new strains through sexual reproduction. The best of them are propagated through apomixis, and the plant has many strains that are well-adapted to localized regions.
Arctic plants benefit greatly from apomictic reproduction. The extreme conditions there make pollination by insects difficult, so it is hard to transfer genetic material from plant to plant. Given the difficult conditions, the plants might benefit from having a few more greatly specialized strains than from the constantly evolving populations that would occur with sexual reproduction.
There is a lot of interest in learning how to genetically manipulate apomictic plants for agricultural reasons. There are, however, technical difficulties in doing so. Plants that are apomictic frequently exhibit polyploidy, meaning they have more than two copies of their chromosomes. This can make gene transfer difficult.
An advantage to using apomictic seed would be that small farmers would be able to produce their own seeds of elite cultivars. Viral diseases can spread through vegetatively propagated plants, and this could be minimized by cloning with seed cultures. One could also take advantage of 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 plant’s reproductive haploid multicellular structure. Being haploid means that it only contains one set of chromosomes. The gametophyte produces gametes — mature reproductive cells that normally would 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 sporophytic apomixis. In this case, the embryos are formed like buds directly from integument tissue. This is part of the inner tissue of the ovule, the structure that holds the embryo sac. The embryo sac continues with its development, while the sporophytic embryo will go ahead to form apomictic seeds. This process is also known as adventitious embryony. Except for commonly occurring in citrus plants, sporophytic apomixis is a rare process in higher plants.
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Discussion Comments
One of my favorite ways of propagating my garden inexpensively is by gathering seeds from my favorite flowering plants. I am not sure if this is the same thing as apomixis or not.
At the end of the season when the plant is at the end of their flowering I will gather the seeds and keep them in a dry place until the next spring. I know the seeds I gather from the mother plant will produce the same kind of plant the next year.
While it is the same kind of plant, I never know for sure what color I will get. This is always kind of fun seeing what the color will be when I plant seeds every year. If I gather seeds from a red petunia plant, I never know if I am going to get red, pink or purple flowers.
I have blackberry bushes that grow along the fence behind my property and I seem to have more of them every year. I will often transplant them to another area, or give some to friends who want to grow blackberries.
I didn't plant these from seed as they were already growing on the place before we bought it. Who knows how long they have been there, but I look forward to their fruit every year.
I wonder if most plants that reproduce by the way of apomixis are very prolific. This article gives the example of dandelions and blackberries which I am very familiar with. We live in the country and have an abundance of these flowering plants every year. I never do anything with either of them, but just know that they will be there every year and often reproduce like crazy.
I don't understand much about the science behind how plants reproduce, I just know that my yard is full of dandelions every year. We used to spray for these to get rid of them, but that all changed once we got a couple of honeybee hives.
Dandelions are one of the first flowers that honeybees like to gather nectar from in the spring. Since we wanted to give our bees plenty of food sources and didn't want the chemicals on our lawn anymore, we don't spray anymore, and look forward to the dandelions every spring.
What I find interesting is that dandelions can reproduce asexually through seed without pollination, yet this is one of the flowering plants that you always see honeybees (which are pollinators) feeding on.
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