Mycorrhiza is an example of symbiotic association. Explain the functions of the partners involved in this interaction.
Answers
Mycorrhizae are symbiotic relationships that form between fungi and plants. The fungi colonize the root system of a host plant, providing increased water and nutrient absorption capabilities while the plant provides the fungus with carbohydrates formed from photosynthesis. Mycorrhizae also offer the host plant increased protection against certain pathogens.
Approximately 90% of all vascular land plantslive in some association with mycorrhizal fungi. Mycorrhizal associations are seen in the fossil record and are believed to be one of the contributing factors that allowed early land plants, including Aglaophyton major (one of the first land plants), to conquer the land.
Mycorrhizal fungi encompass many major groups of the fungus Kingdom and in the past were divided into two non-evolutionarily related groups: the ectotrophic and endotrophic based upon the position of the fungal hyphae in relation to the tissues of a plants roots. Ectomycorrhizal fungi ensheath the root cells but usually do not penetrate them (extracellular). Endomycorrhizal fungi penetrate and enter the cells of a plant root (intracellular).
Modern research has lead to the recognition of seven types of mycorrhizal fungi, subdividing the old, traditional groups. The new nomenclature is often more precise and specific to the associated plant taxa. The relatively homogenous ectomycorrhizal group largely remains with only the addition of the subgroup ectendomycorrhizas. The endomycorrhizal group has been dismantled, but specific types are now recognized: Vescicular-Arbuscular Mycorrhizas, the Orchid mycorrihzas, and those which associate with the Ericaceae (Blueberry family): the Arbutoid, Monotropoid and Ericoid mycorrhizas.
Fungi are heterotropic organisms, and must absorb their food. Fungi also have the ability to easily absorb elements such a phosphorus and nitrogen which are essential for life. Plants are autotropic, producing their food in the form of carbohydrates through the process of photosynthesis. However, plants often have difficulty obtaining and absorbing many of the essential nutrients needed for life, specifically nitrogen and phosphorus.