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Lecture 18
- Glomeromycota
- Mycorrhizal Associations
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http://www.ffp.csiro.au/research/mycorrhiza/vam.html#fungi
Glomeromycota(Vesicular) Arbuscular endomycorrhizal fungi, or (V)AM fungi
Mycorrhizal root system washed carefully from coarse sand to reveal the
intact network with external hyphae (arrow) with spores (S) produced by
Glomus mosseae. (bar = 100 um)
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- small group of about 130 described morphological species;
--- associated with ca. 300,000 plant species (ca. 80 - 90 % of of land plants);
- coenocytic hyphae ==> previously included in the Zygomycota, Order Glomales
- multinucleate asexual spores can contain up to 5,000 nuclei.
- sexual stage never observed in any member of the Glomales
--- clonality?
------ but extreme genetic variation of ribosomal DNA sequences is found within a single spore; still no data
for other genes; these organisms are difficult to work with at the molecular level.
- molecular data do not indicate monophyly between Zygomycota and Glomales
---- Glomeromycota are probably sister group to Asco-Basidio
==> the phylum Glomeromycota has been suggested by Schüssler et al., 2001.
- somatic hyphae are similar in all taxa.
- little variation in the shape of arbuscules and vesicles (the latter not always present),- spores provide the most useful charcteristics for differentiation of species.
More info from: http://www.ffp.csiro.au/research/mycorrhiza/vam.html#fungi
Glomeromycota(Vesicular) Arbuscular endomycorrhizal fungi, or (V)AM fungi
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http://www.ffp.csiro.au/research/mycorrhiza/vam.html#fungi
Structures in Soil- Hyphae - A network of hyphae forms in the soil with
thicker hyphae which function as conduits and thin
branched hyphae which are thought to absorb
nutrients.
- Spores - Large (for a fungus) asexual spherical
structures (20-1000+ um diameter) that form on
hyphae in soil or roots.
Structures in Roots
- Hyphae - these are non-septate when young and
ramify within the cortex.
- Vesicles - storage structures formed by many fungi.
- Arbuscules - intricately branched haustoria in cortexcells.
.
Arbuscules
Glomeromycota (AM fungi)
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http://www.ffp.csiro.au/research/mycorrhiza/vam.html#fungi
Glomeromycota (AM fungi)
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http://www.ffp.csiro.au/research/mycorrhiza/vam.html#fungi
Soil hyphae produce appressoria
between epidermal root cells (arrows)
to penetrate plant tissue.
(Bar = 100 um)
Hyphae at an entry point (E) penetrating cortex cells (arrows).
(Bar = 100 um)
Glomeromycota (AM fungi)
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http://www.ffp.csiro.au/research/mycorrhiza/vam.html#fungi
Colony of a VAM fungus spreading from
the entry point (E) by convoluted hyphae in
the inner cortex of an Erythronium
americanum root.
(Bar = 100 um)
Mature arbuscule of Glomus mosseae with
numerous fine branch hyphae
(Bar = 10 um).
Glomeromycota (AM fungi)
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http://www.ffp.csiro.au/research/mycorrhiza/vam.html#fungi
Vesicles (V) produced by a Glomus species
in a leek root. This root also contains many
intercellular hyphae.
(Bar = 100 um)
Lobed vesicles of an Acaulospora species in
a clover root.
(Bar = 100 um).
Glomeromycota (AM fungi)
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http://www.ffp.csiro.au/research/mycorrhiza/vam.html#fungi
Lab techniques
Spores can be separated from soil then
sorted into categories based on size andcolour. The image on the right shows
how spores (S) on a piece of filter
paper can be used to start a "pot
culture" using pasteurised soil in which
a host plant will be grown.
Glomeromycota (AM fungi)
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- three families and six genera;.
Gigasporaceae : Gigaspora and Scutellospora
- form only arbuscules (no vesicles) in roots.
Acaulosporaceae: Acaulospora and Entrophospora
- produce both vesicles and arbuscules in roots
- produce "chlamydospores" in the soil
- spores embedded in a swollen, sac-like structure
-- Aculospora the spore forms laterally on the hyphae-- Entrophospora spore develops ‘within the neck’ of the hyphae
Glomaceae: Glomus and Sclerocystis
- produce both vesicles and arbuscules in roots
- chlamydospores are borne apically.
Spore of
Glomus clarum
Spore of Acaulospora sp.
Pics from http://www.ffp.csiro.au/research/mycorrhiza/vam.html#fungi
Glomeromycota (AM fungi)
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http://www.berkeley.edu/news/media/releases/2000/09/14_funghi.html
Light microscope picture
of a fossil fungal spore
with attached hypha fromthe Ordovician, 460
million years ago.
(c)Science Magazine
CREDIT: Dirk
Redecker/UC Berkeley
Fossils from a Wisconsin roadcut show clearly thatfungi and green plants moved from water onto land atabout the same time, bolstering the theory that fungihelped plants successfully invade the land.
This particular fossil shows no evidence of association
with plants, however other Devonian fossils (400
million years ago) have been shown to containstructures indicative of arbuscular mycorrhizae.
http://mycorrhiza.ag.utk.edu/muthukumar7.htm
Glomus
geosporum
spore
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Fungal benefits
- carbohydrates (= photosynthetic products) ==> converted to trehalose, mannitol, glycogen which are
necessary cofactor for spore germination.
Plant benefits- hyphae extend into the soil away from roots
---> increase the potential for water absorption
---> increase the potential for phosphorus uptake
- currently debated to what extent, if any, fungi increase nitrogen uptake by host plant
- endomycorrhizal associations may contribute to the resistance to certain root pathogens including various
fungi and nematodes by production of antibiotic substances
Two major types : AM vs. ECTO
- AM penetrates cortex cells ; ECTO do not
- ca.130 AM species for 300,000 plant species- > 5000 ECTO species for 2000 plant species
- ECTO: mostly trees
- AM: woody & herbaceous plants
Mycorrhizal symbiosis
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Mycorrhizal symbiosis
From Kendrick
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Mycorrhizal symbiosis
From Kendrick
The Hartig net
and mantle are
typical of ectomycorrhiza
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Mycorrhizal symbiosis : Ectomycorrhiza
Pics from http://mycorrhiza.ag.utk.edu/mrecent.htm
Lactarius deliciosus on Pinus pinaster root tips
Tuber puberulum on Picea abies root tips
Thelephoroid
ectomycorrhiza
On Douglar fir
double colonization
by Tomentella
sublilicina andThelephoroid#2 on
Bishop pine
unknown
boletoid fungus
on bishop pine
http://plantbio.berkeley.edu/~bruns/
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Mycorrhizal symbiosis : Ectomycorrhiza
(A) penetration of hyphae between the cells of the root
cortex to form a characteristic Hartig net
(B) establishment of a mantle of hyphae
around the outside of the root (the brown layer
in the picture below);
(C) extension of hyphae from the
mantle into the surrounding soil
From Kendrick
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Mycorrhizal symbiosis : Ectomycorrhiza
Basidiomycotina euagarics
Amanita
Hygrophorus
Tricholoma
Cortinarius
Inocybe
bolete clade
about 15 traditional bolete genera, including
Boletus, Suillus, Leccinum etc.
Scleroderma
Russuloid clade
Russula, Lactarius
Thelephoroid clade
Thelephora, Tomentella
Cantharelloid clade
Cantharellus
...
Ascomycotina
Pezizales
Pezizaceae (1 genus)
Balsamiaceae (3)
Otideaceae (1)Helvellaceae (1)
Pyronemataceae (3)
Terfeziaceae (4)
Tuberaceae (2)
Elaphomyces
Taxonomic Distribution of Ectomycorrhizal (EM) FungiAbout 90 genera and 5,000 species
Major taxa
Adapted from Kendrick
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Other morpho-types than AM and EM exist, but are less widespread.
For instance:
- orchid mycorrhizas;
- ericaceous mycorrhizas (mostly Ericales species)
--- ericoid mycorrhizes;--- arbutoid mycorrhizas
--- monotropoid mycorrhizas
Mycorrhizal associations: Non AM or ECTO types
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Mycorrhizal associations
From Kendrick
The fungus enters cells of the
root cortex ands develops coils
or pelotons which eventually
swell, degenerate and are
absorbed by the plant cell.
Orchid mycorrhizas
- Orchid seeds need a fungus to germinate
--- plant depends on the fungus until chlorophyll-bearing leaf develop (can take 1-2 years)
- commonly, these fungi are basidiomycetous anamorphs of the
genus Rhizoctonia
--- holomorphs mostly in genera Thanatephorus, Corticium, and
Ceratobasidium--- Sebacina and Tulasnella species also commonly found.
Note: We can now use molecular identification.
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Mycorrhizal associations
Orchid mycorrhizas
Different possible outcomes of seedling colonization by a fungus:
(1) the seed becomes colonized by an appropriate fungus and thrives;
(2) the fungal infection takes over, and kills the seedling;
(3) the fungal invasion fails, the fungus is eliminated, and the seedling stops growing.
==> it does not appears to be a true mutualistic symbiosis
Further specialization / dependence: achlorophyllous orchids, e.g., in genus Corallorizha
-- other (ecto-!) fungi, e.g. Russula, Sebacina, etc…
--gain for the fungus? Is the plant “cheating” ?
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Arbutoid / Ericoid mycorrhizas
- intermediate between ecto- and endo-mycorrhizas:
---- sheathing fungal mantle and typical ecto- branching;
---- the fungus penetrates the cortical cells and fills them with
densely coiled hyphae (not arbuscules as in VAM)
- Arbutoid type: Hartignet present
- Ericoid type: does not produce a typical Hartig net
- characteristics ofEricales (rhododendrons, blueberrys, etc.)
--- but can also (more rarely) be formed in other plant families,
e.g., Fagaceae.
- predominant in low pH soils and high altitudes and latitudes
(Heath soils, tundra)- tend to be present in pioneer species.
- apparently transfer nitrogen, but not phosphorus, to the host.
Some fungi can form normal ectomycorrhizas with several
ectotrophic tree families and ericoid mycorrhizas with
members of the Ericaceae===> “plant signal”
Some fungi are restricted to Ericaceae and only form ericoid
mycorrhizas.
Mycorrhizal associations
From Kendrick
Ericoid type
coiled hyphae
(intracellular)
sheathing
fungal mantle
See http://botit.botany.wisc.edu/courses/mpp/EricadMyco.html for more detailed info
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Monotropoid mycorrhizas
- known only with the achlorophyllous plant
Monotropa (‘Indian pipe’)
===> the plant (achlorophyllous) cannot provide
carbohydrates to a fungal mycorrhizal partner…
so what? “cheating” !
- the fungus produces a Hartig net and ahaustorium-like peg into root cell.
- Fungi involved: Tricholoma, Russula, Boletus;
all typical ecto-
- tri-ways relationship--- it has been shown that the fungus also has a
normal mycorrhizal relationship with a
neighboring plant.
Mycorrhizal associations
haustorium-
like peg
Hartig net
From Kendrick
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Evolution of ericaceous mycorrhizas in the Ericales
http://botit.botany.wisc.edu/courses/mpp/EricadMyco.html
arbutoid mycorrhizas
monotropoid mycorrhizas
ericoid mycorrhizes;
Unknown status?
Recent studies:
Bidartondo, M. I.& Bruns, T. D. 2002. Fine-level mycorrhizal specificity in the Monotropoideae
(Ericaceae): specificity for fungal species groups. Molecular Ecology 11(3): 557-569.
M. I. Bidartondo and T. D. Bruns. 2001. Extreme specificity in epiparasitic Monotropoideae (Ericaceae):
widespread phylogenetic and geographical structure. Molecular Ecology 10(9): 2285 - 2295.
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