Mycorrhiza is the mutualistic symbiotic association between certain kinds of fungi and the roots of vascular plants.
- Derived from Greek words ‘mukes’- fungus and ‘rhiza’- roots.
- Approximately 90% of the roots of plants were found to be associated with heterogeneous fungal taxa.
- Developing roots of the plants are encircled by the fibrous fungal networks and reach through the root cells by penetrating the epidermal layer.
- Both plants and fungi benefit through this association, which is called a symbiosis relationship.
- It also acts as parasite depending upon the species requirement with the host plants.
- However, sometimes the host plant species may be harmed by the fungal encounter that it contemplates through its defense mechanism.
- But, often the association is mutualistic.
- The structure of mycorrhizal roots can only be seen under a microscope, not from the naked eye.
Interesting Science Videos
Mutual Benefits of Mycorrhizal Associations between Fungi and Plant
| Benefits to Fungi | Benefits to Plants |
| Fungi get nourishment from roots cortical cells. | Plants’ surface area for absorption increases. |
| Fungi get constant and direct access to carbohydrates such as sucrose. | Plants get an enhanced supply of water, Nitrogen, Phosphorus, and Sulfur essential for nutrient cycling. |
| Fungi expand their mycelium, aiding the colonization of new substrates. | Plants are benefitted with the improve root environment resulting in better growth and development. |
| Fungi expands their mycelium, aiding the colonization of new substrates. | Plants are benefitted with the improve root environment resulting in the better growth and development. |
Types of Mycorrhiza
Mycorrhiza are classified into the following types based on their morphological and anatomical features:
A. Ectomycorrhiza
In this, fungal partner grows on the outer surface of plant roots as a sheath. A sheath of fungal hyphae encloses plant roots-fungal mycelium penetrates between cells in the cortex of the root. Extensive invasion of the plant is uncommon, but rudimentary hyphae from the fungus can penetrate the epidermal layer of the roots. It is termed Hartig Net, the region where the fungal and plant symbionts are adjacent to each other performing nutrients and carbon exchange. The colonization of root tips by ectomycorrhizal fungi suppresses the development of root hairs and changes the branching patterns of the host plant’s roots. It is because fungi induce altered levels of cytokinins, which in turn stimulate increased root branching in the host plant. This physical adaptation helps the plant maximize the surface area of its root system, which is beneficial for nutrient and water absorption in the mycorrhizal symbiosis association. Scleroderma cepa, Laccaria bicolor, Rhizopogon luteolus, etc are some examples of Ectomycorrhizal Fungi.
B. EndoMycorrhiza
In this, the fungal partner lives entirely within the root tissues. The fungal component is predominantly internal to the root structure, with fungal penetration into host cortical cell walls. The hyphae penetrating the cortical cells, create a greater contact surface area which heightens and facilitates the greater exchange of source of carbons and other macronutrients.
It is classified into five types:
1. Arbuscular Mycorrhiza (AM or VAM)
Arbuscular Mycorrhiza is the mycorrhizal association formed by phylum Glomeromycotan fungi with many vascular plant species (grasses, herbs, trees). Fungal Hyphae penetrate plant cortical cells, push side cell membranes, and branch into tree-like arbuscular structures. This maximizes the contact surface area between the fungus and host cells. Some fungi also produce storage structures, (vesicles) within the root tissues. So, it is termed as both Arbuscular Mycorrhiza / Vesicular-Arbuscular Mycorrhiza.
2. Orchidoid Mycorrhiza
This mycorrhizal association occurs in the roots of the orchid, where an expansive intracellular mycelium is formed. It belongs to the family Basidiomycetes involving genera like Rhizoctonia (with teleomorphs Tulasnella, Sebacina, Thanatephorus, Ceratobasidium, Armillaria, Fomes, etc.).These fungi can co-occurrence with other mycorrhizae like Ectomycorrhizae and Arbuscular mycorrhizae forming robust mycorrhizal associations benefitting the orchids in seed development, nutrient uptake in an early stage of development. This is a delicate symbiosis, the Orchid forms an antifungal chemical, by breaking down intracellular hyphoil coils which prevent them from fungus.
3. Arbutoid Mycorrhiza
The fungal association with the family Ericaceae plants includes Arbutus, Arctostaphylose, and Pyrolaceae. The fungi are basidiomycetes which form Ectomycorrhizal association. A thin layer of fungal sheath surrounds the plants’ root from outside and fungal hyphae penetrate between epidermal and outer layers of cortical cells, forming paraepidermal Hartig Net. Unlike Ectomycorrhiza, the hyphae invade the cortical cell and form hyphoil coils within them. Thus, through the ectomycorrhizal association between the aurbotoid plants and adjacent tree species exists the exchange of nutrients source and other essential photosynthates.
4. Ericoid Mycorrhiza
It involves the restricted group of Fungi such as Ascomycota and Deuteromycota with plant species of Ericaceae, Epacridaceae, and Empetraceae. They show similar characteristics as Arbutoid Mycorrhiza, which invades the cortical cells forming hyhoil coils inside epidermal cells. These mycorrhizal fungi supply nitrogen to the plants as the fungi involved have proteinase secretion properties which help in accessing the nitrogen source present in the soil to the plants.
5. Monotropoid Mycorrhiza
The plants involved in this association are non-chlorophyllous Monotropa with Fungi of species Basidiomycetes, especially Boletes. These fungus forms ectomycorrhizal associations with other plants such as conifers and transfer essential nutrients source to the non-chlorophyllus Monotropa. This association is similar to the Orchid Mycorrhiza. As they cannot make their food from photosynthesis they depend upon fungi fully. Fungal threads penetrate and grow inside the cells of the Monotropa plant but are restricted to outer cells, hence the fungi form peg-like structures within these epidermal cells when nutrient exchange takes place.
C. Ectendomycorrhiza
This mycorrhiza association has characteristics of both Ectomycorrhiza and Arbuscular Mycorrhiza. Initially, the fungi involved in this association were difficult to identify due to their absence in fruiting structure. However now, with further analysis, the fungi are identified as ‘E- strain’ Fungi. Which belongs to the genus Wileoxins, within the Ascomycota Phylum, order Pezizales. These Mycorrhiza are structurally and developmentally very similar to the Ectomycorrhiza, except for its properties of intracellular hyphal penetration.
Significances of Mycorrhiza
- Mycorrhizal associations enhance the chance of plant survival under conditions of salinity and drought stress.
- Mycorrhizae can act as a potential disease control agent by providing resistance against soil and root-borne pathogens.
- Mycorrhizal associations contribute to soil conservation and help in stabilizing soil structure.
- The water-holding capacity of the soil increases.
- Mycorrhizae can help plants avoid the uptake of Arsenate, which is a toxic compound.
- Mycorrhizae facilitate the uptake of phosphorus (P) and other immobile nutrients, such as zinc (Zn), cobalt (Co), magnesium (Mg), iron (Fe), and copper (Cu), which are essential for plant growth and development.
- It enhances the mineral weathering in the soils.
- Mycorrhizae can help increase the production of plant hormones, such as auxins and cytokinins, which are essential for the initiation and development of flowers and fruits.
- They can help optimize the use of fertilizers, particularly phosphorus, by improving the plant’s ability to access and utilize these essential nutrients. This can contribute to increased productivity and sustainability in agricultural and horticultural systems.
- In this association, biodiversity is enhanced, as a variety of plant species grows in different ecosystems.
References
- Futai, K., Taniguchi, T., & Kataoka, R. (2008). Ectomycorrhizae and their importance in forest ecosystems. Mycorrhizae: sustainable agriculture and forestry, 241-285.
- Balestrini, R., & Lumini, E. (2018). Focus on mycorrhizal symbioses. Applied soil ecology, 123, 299-304.
- Chandwani, S., Maiti, S., & Amaresan, N. (2023). Fungal mycorrhizae from plants roots: functions and molecular interactions. In Microbial Symbionts (pp. 133-160). Academic Press.
- Parniske, M. (2008). Arbuscular mycorrhiza: the mother of plant root endosymbioses. Nature Reviews Microbiology, 6(10), 763-775.
- Zhang, Y., Zeng, M., Xiong, B., & Yang, X. (2003). Ecological significance of arbuscular mycorrhiza biotechnology in modern agricultural system. Ying Yong Sheng tai xue bao= The Journal of Applied Ecology, 14(4), 613-617.
- Mycorrhizal associations: Arbuscular mycorrhizas. (n.d.). https://mycorrhizas.info/vam.html
- Moore, D. (2011, June 1). Arbutoid mycorrhizas. David Moore. https://www.davidmoore.org.uk/assets/mostly_mycology/diane_howarth/arbutoid.htm
- Orchids, fungi & symbioses. (n.d.). Smithsonian Environmental Research Center. https://serc.si.edu/research/research-topics/biodiversity-conservation/orchids-fungi-symbioses
- Volk, T. J. (2013). Fungi. In Elsevier eBooks (pp. 624–640). https://doi.org/10.1016/b978-0-12-384719-5.00062-9
- Libretexts. (2023, October 31). 31.3B: Mycorrhizae- The Symbiotic Relationship between Fungi and Roots. Biology LibreTexts. https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/General_Biology_(Boundless)/31%3A_Soil_and_Plant_Nutrition/31.03%3A__Nutritional_Adaptations_of_Plants/31.3B%3A_Mycorrhizae-_The_Symbiotic_Relationship_between_Fungi_and_Roots