Mycorrhiza Fungus + Plant Host (Root)
Root Anatomy
Mycorrhizal fungi Cryptomycota http://www.mykoweb.com/articles/index.html#apm1_4
Summary Mycorrhizal symbioses are mutualistic Fungal benefits carbohydrates (photosynthate, monosaccharides) that are converted to trehalose, mannitol, glycogen necessary cofactors for spore germination Plant benefits greater absorptive area uptake of P, N, Ca, K, Cu, Mb, Mg, Zn water protection against soil borne pathogens
Angiosperms and types of mycorrhizae There are two distinct types of mycorrhizal associations among the Gymnosperms. The majority of species have vesicular-arbuscular mycorrhizae. However, all of the Pinaceae, are ectomycorrhizal. All vascular spore producing plants form vesicular-arbuscular Mycorrhizae.
The table below shows a summary of the characteristics of the 7 mycorrhizal types. http://www.davidmoore.org.uk/assets/mostly_mycology/diane_howarth/mycorrhizal%20types.htm AM Ecto Ectendo Ericoid Arbutoid Monotropoid Orchid Fungi septate - + + + + + + Fungi aseptate + - - - - - - Intracellular colonisation + - + + + + + Fungal sheath - + + or - - + or - + - Hartig net - + + - + + - Vesicles + or - - - - - - - Achlorophylly - (?+) - - - - + +* Fungal taxa Glom Basidio/ Asco/Zygo Basidio/ Asco (Zygo) Asco/Basido Basidio Basidio Basidio/Asco Plant taxa Bryo Pterido Gymno Angio Gymno Angio Gymno Angio Ericales Bryo Ericales Monotropaceae Orchidaceae All orchids are achlorophyllous in the early seedling stages, but usually chlorophyllous as adults.
VAM/AM endomycorrhizae: occur in the fine root system of vascular plants, hyphae penetrate the cortex cells forming vesicles and arbuscules Arbuscules - highly branched structures that are the site of nutrient transfer; they do not penetrate cell membrane; short-lived structures Vesicles - oval-shaped, darkly staining structures that are thought to function as nutrient reservoir
Hyphae that extend into Substrate (soil, littler, et. Ectomycorrhiza
Roots colonized by ectomycorrhizal fungus! < hyphae thickened, short, roots
Ectomycorrhizal Root Cross Section 1. fungus mantel 2. hartig net 3. root cortext 4. stele (xylem & phloem) < Hartig net (arrows) Fungus mantel Hartig Net & Mantel stele corte x
Root Cross Section with Ectomycorrihza Hartig Net Mantel
The ectomycorrhizal fungus surrounds the root tip with a thick mantle of closely appressed hyphae, whereas the Hartig net develops around epidermal cells (green). In the case of arbuscular mycorrhizas, the root tip is usually not colonized. Hyphae develop from a spore and produce a hyphopodium on the root epidermis. Intraradical colonization proceeds both intra and intercellularly and culminates with the formation of arbuscules, little fungal trees, inside inner cortical cells (brown). THE TWO MOST COMMON MYCORRHIZAE!
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Ericoid mycorrhizae help ericaceous plants survive on sites with slow decomposition (bogs, arctic, sand, etc.) Ericoid mycorrhiza of salal, Gaultheria shallon. Dark blobs are masses of fungal hyphae in cortical cells of root. Hyphae up to 80% of mass of root, but do not penetrate cell membrane.
Ericaceous mycorrhizas Ericaceae often grow in nutrient-poor, acidic soils; these plants have unusually fine roots Ericoid type with endophytic mycobiont forming intracellular hyphal coils in epidermal cells with members of tribes Ericeae, Vaccineae, Rhododendreae, Calluneae Ascomycetous and Basidiomycetous fungi
Orchids and their mycobionts The orchid family is one of the largest families of flowering plants, with over 23,000 species, distributed mainly in the tropics. The family includes both terrestrial and epiphytic species.
Orchid Seed Orchids produce millions of tiny, dust-like seed that lack endosperm
Orchid mycorrhizas All orchid seed require infection by a fungus in order to germinate under natural conditions
Orchids have a prolonged seedling stage during which they are unable to photosynthesize, and during this time obtain their nutrients via the fungus
Orchid mycorrhizas Two types of mycobionts associated with orchids Intracellular mycobiont forms hyphal coils (pelotons) and supplies seedling with carbon during heterotrophic state Mature plants of nonchlorophyllous plants form second type of mycorrhiza with clampforming fungus that forms mantle and Hartig net (not covered here)
Pelotons inside root cells of mature orchids; hyphal coils break down to release nutrients to the plant cell