What is the Difference Between Parasitic Roots and Mycorrhizae

The main difference between parasitic roots and mycorrhizae is that the parasitic roots are adventitious roots of parasitic plants, penetrating into the conducting tissues of the host plant whereas mycorrhizae are the associations between fungi and roots of higher plants. 

Parasitic roots and mycorrhizae are two types of symbiotic associations of root-like structures with plants. Furthermore, parasitic roots are harmful as they acquire water and nutrients from the host plant while mycorrhizae are beneficial for both fungal and plant partner.

Key Areas Covered

1. What are Parasitic Roots
     – Definition, Structure, Role, Examples
2. What are Mycorrhizae
     – Definition, Structure, Role, Examples
3. What are the Similarities Between Parasitic Roots and Mycorrhizae
     – Outline of Common Features
4. What is the Difference Between Parasitic Roots and Mycorrhizae
     – Comparison of Key Differences

Key Terms

Mutualism, Mycorrhizae, Parasitic Roots, Parasitism, Symbiotic Relationships

What are Parasitic Roots

Parasitic roots are the modified roots of parasitic plants used to penetrate tissues of the host plant up to the conducting tissues. Generally, they are adventitious roots which arise from the nodes of the parasitic plant in the form of peg-like projections called haustoria. The main function of the roots of the parasitic plants that are photosynthetic is to obtain water and mineral nutrients. Thus, this type of parasitic plants is known as hemiparasites. Some examples of hemiparasites are the Nuytsia floribunda (Western Australian Christmas tree), which is an obligate root hemiparasite, Rhinanthus (e.g. Yellow rattle), which is a facultative root hemiparasite, and mistletoe, which is an obligate stem hemiparasite.

Figure 1: Mistletoe

On the other hand, some parasitic plants obtain all the sugars from the host plant. Thus, this type is known as holoparasites and they have colors other than green. Some examples of holoparasites are dodder, which is a stem holoparasite, and Hydnora spp., which are root holoparasites. However, only parasitic plant benefits by this type of symbiotic relationships; it is harmful to the host plant. Therefore, it is considered as a parasitic relationship.

What are Mycorrhizae

Mycorrhizae or fungus-roots is a symbiotic association of a fungus and the roots of higher plants. Here, both the higher plant and the fungus partner benefit from their relationship. This means the plant provides sugars produced by photosynthesis to the fungus. On the other hand, the fungus absorbs water and nutrients such as phosphorus for the plant. Therefore, the relationship between them can be considered as a mutualistic relationship.

Figure 2: Mycorrhizal Root Tips

Furthermore, the fungus colonizes in the root tissues of the higher plant. Generally, arbuscular mycorrhizal fungi (AMF or AM) forms intracellular colonies while ectomycorrhizal fungi form extracellular colonies. On the other hand, most plant families excluding Brassicaceae and Chenopodiaceae form this type of associations.

Similarities Between Parasitic Roots and Mycorrhizae

• Parasitic roots and mycorrhizae are two types of symbiotic relationships maintained with plants.
• These relationships are important for obtaining water and nutrients and sometimes shelter.

Difference Between Parasitic Roots and Mycorrhizae

Definition

Parasitic roots refer to the modified roots of parasitic plants, penetrating the host plants, and connecting them to the conductive system while mycorrhizae refer to the fungi which grow in association with the roots of a plant in a symbiotic or mildly pathogenic relationship. Thus, this is the fundamental difference between parasitic roots and mycorrhizae.

Significance

Therefore, the main difference between parasitic roots and mycorrhizae is that while the parasitic roots are the adventitious roots of parasitic plants, mycorrhizae are associations of a fungus and the roots of higher plants.

Role

Parasitic roots are responsible for absorbing water and nutrients from the host plant while the plant provides sugars to the fungus and the fungus provides water and nutrients such as phosphorus to the plant in mycorrhizae. Hence, this is a very important difference between parasitic roots and mycorrhizae. 

Type of Symbiotic Relationship

Furthermore, parasitic roots maintain a parasitic relationship with the plant, harming it, while mycorrhizae maintain a mutualistic relationship in which both parts are benefited. So, this is also a difference between parasitic roots and mycorrhiza.

Conclusion

Parasitic roots are the modified roots of parasitic plants. They are adventitious roots which penetrate the tissues of the host plant to the conducting tissues and they absorb water or both water and nutrients from the host. On the other hand, mycorrhizae are a symbiotic association between a fungus and the roots of higher plants. Here, fungus supplies water and nutrients to the plant from the soil while the plant provides sugars for the fungus. Thus, parasitic roots are harmful while mycorrhizae are beneficial. Therefore, the main difference between parasitic roots and mycorrhizae is the type of relationship between the two partners.  

References:

1. “Parasitic Plants.” Cronodon, Available Here.
2. VanSomeren, L., “How Do Mycorrhizae Work? Explained Simply.” Untamed Science, Available Here.

Image Courtesy:

1. “Mistletoe, coming soon to a market near you – geograph.org.uk – 1585249” By Pauline Eccles (CC BY-SA 2.0) via Commons Wikimedia   
2. “Mycorrhizal root tips (amanita)” By Ellen Larsson – R. Henrik Nilsson, Erik Kristiansson, Martin Ryberg, Karl-Henrik Larsson (2005). “Approaching the taxonomic affiliation of unidentified sequences in public databases – an example from the mycorrhizal fungi”. BMC Bioinformatics 6: 178. DOI:10.1186/1471-2105-6-178. (CC BY 2.5) via Commons Wikimedia