Angiosperms may reproduce asexually by means of modified stems, roots, or leaves. Asexual reproduction is advantageous when a plant has a superior genotype well adapted to its environment, but it can decrease the genetic diversity of plant populations. Seeds and fruits, normally the result of sexual reproduction, can form asexually through apomixes.
learning outcomes
You should be able to:
Compare and contrast sexual and asexual reproduction in plants, including both the end result and the advantages or disadvantages.
List types of locations where vegetatively reproducing plants might occur, and give reasons for their occurrence in these locations.
Describe how apomixis occurs and how this might be useful in agriculture.
What are the advantages and disadvantages of asexual reproduction in plants? What are the advantages and disadvantages of sexual reproduction?
Asexual reproduction is rapid, and it conserves the genetic adaptations of a plant. However, in asexual reproduction genetic homogeneity makes the offspring and population derived from it susceptible to a changing physical or biological environment, since the phenotypes in the population are all the same. Sexual reproduction produces genetic diversity in offspring and the population derived from it, and the phenotypic diversity makes the population adaptive in a changing environment. However, sexual reproduction is a slower process than asexual reproduction.
In what types of situations might asexual reproduction in plants be adaptive?
Asexual reproduction can occur without the need for pollination, producing many plants quickly. Many grow by means of stolons or rhizomes, which make them well adapted for poor or eroded soils, such as those on hillsides, or as pioneer plants in unstable soils such as sand dunes. Asexual reproduction is also adaptive in deserts, where it may be difficult for seedlings to become established.
The isolation of a mutation in the Arabidopsis SWII gene that results in abnormal meiosis has offered insights into apomixis. How would you try to identify other genes or mutations that function along with the gene product of SWII, with the goal of producing fully fertile apomictic plants?
Several approaches might be taken, such as a genetic screen for meiotic cells that do not separate chromosomes at anaphase I, or a search for proteins (and then their genes) that bind to SWII protein.
You have seen how angiosperms reproduce sexually and asexually. A disadvantage of asexual reproduction is that its genetic inflexibility may leave a population unable to cope with new challenges. In the next chapter we will focus on the mechanisms that have evolved in plants to cope with biological and physical challenges in their environment.