BOT301-05_L18.pdf

7/17/2019 BOT301-05_L18.pdf

http://slidepdf.com/reader/full/bot301-05l18pdf 1/23

Lecture 18

- Glomeromycota

- Mycorrhizal Associations

7/17/2019 BOT301-05_L18.pdf


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)

7/17/2019 BOT301-05_L18.pdf


- 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

7/17/2019 BOT301-05_L18.pdf



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)

7/17/2019 BOT301-05_L18.pdf




7/17/2019 BOT301-05_L18.pdf



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)


7/17/2019 BOT301-05_L18.pdf



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).


7/17/2019 BOT301-05_L18.pdf



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).


7/17/2019 BOT301-05_L18.pdf



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.


7/17/2019 BOT301-05_L18.pdf


- 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


7/17/2019 BOT301-05_L18.pdf


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

7/17/2019 BOT301-05_L18.pdf


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

7/17/2019 BOT301-05_L18.pdf



From Kendrick

7/17/2019 BOT301-05_L18.pdf



From Kendrick

The Hartig net

and mantle are

typical of ectomycorrhiza

7/17/2019 BOT301-05_L18.pdf


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/

7/17/2019 BOT301-05_L18.pdf



(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

7/17/2019 BOT301-05_L18.pdf



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

7/17/2019 BOT301-05_L18.pdf


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

7/17/2019 BOT301-05_L18.pdf


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.

7/17/2019 BOT301-05_L18.pdf



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” ?

7/17/2019 BOT301-05_L18.pdf


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.


From Kendrick

Ericoid type

coiled hyphae

(intracellular)

sheathing

fungal mantle

See http://botit.botany.wisc.edu/courses/mpp/EricadMyco.html for more detailed info

7/17/2019 BOT301-05_L18.pdf


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.


haustorium-

like peg

Hartig net

From Kendrick

7/17/2019 BOT301-05_L18.pdf


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.

Date post:	07-Jan-2016
Category:	Documents
Upload:	walter-macasiano-gravador
View:	2 times
Download:	0 times

BOT301-05_L18.pdf

Documents