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Mycology lecture 6, Fungal Structure and Ultrastructure

Mycology lecture 6, Fungal Structure and Ultrastructure

BASICS


-Essentially a tube


Indeterminate length


-Hyphae grow only at the tips


-Extension zone


-Older parts: autolysis(desctruction of cell through own enzymes) or heterolysis(apoptosis from surround hydrolytic enzymes)


-Most higher Fungi: septa


-Septa have pores; therefore ‘compartments’


-Reproductive areas

BASICS


-Surrounded by a complex wall


-Thin at apex


-Plasma membrane fixed tightly to wall



ULTRASTRUCTURE: structures that are very small and must be viewed with electron microscopy or other means

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The extreme hyphal tip, is the tip of the hypha. What accumulates here?

A lot of membrane bound vesicles accumulate here.

What do these vesicles show?

Vesicles show differences in density



What is lacking at these extreme hyphal tips?

These extreme hyphal tips lack organelles

Where are these organelles located?

These organelles are located farther back

What is the source of these vesicles?

Their source is the Golgi bodies.

What is responsible for the chitin in cell walls?

Chitin synthase.

What is the Apical vesicle cluster(also called Spitzenkorper)?

Its a cluster of vesicles that form at the Apex(hypha tip)

What is in the centre of the Apical Vesicle Cluster?

In the centre of the apical vesicle cluster there is a lack of vesicles.

How do these vesicles get to the hyphae tip?

Actin microfilaments, microtubules, myosin are though to bring vesicles from the golgi to the apex of the hyphae tip.

What happens where there is a shift in the hyphae?

There is a change in direction or branching occur

What is located behind the apex?

Behind the apex you will find mitochondria, it is rich in mitochondria.




This is similar to plants/animals: cistern style

What does the mitochondria do?

Generates a proton-motive force that drives the hyphal tips to uptake nutrients

Next we will be talking about the Subapical region of the hyphae, what does subapical mean?

Subapical means right below the apex.

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What is located further back in the hypha?

Located further back in the hypha is the branched tubular vacuoles.

What do the branched tubular vacuoles do?

They expand through pores to other compartments and act as a transport system for the movement of metabolites(includes phosphates which are often in short supply)

How are the nuclei distributed between the fungal groups?

It varies between fungal groups, coenocytic vs. septate.

What is the nuclei distribution for oomycota?

Several nuclei in each oogonia

What is the nuclei distribution for septate Fungi(ascomycota)?

Two nuclei in each compartment. Can squeeze through pores, so concept is fluid.

What is the nuclei distribution for septate fungi(Basidiomycota)?

It can be both, monokaryon(one per compartment), or dikaryon(two per compartment) which will have a dolipore septum

What do hyphal colonies develop from?

They typically develop from a single spore.

How do hyphal colonies develop from a single spore?

They extend the germ tube; then begin to branch behind the tip.

What does the typical colony form?

A circle

What happens to older hyphae?

The older hyphae fuse back with other hyphae.

What is this process called?

Hyphal anastomosing

What is the point of hypal anastomosing?

To pool together protoplasm to produce other large structures.

What do the hyphae do in nutrient rich conditions?

The branching hyphae diverge from one another.

What controls this behaivour?

It is unknown, but speculated to be CO2 or growth metabolites

What do the hyphae do in nutrient poor conditions?

The centre hyphae grow towards each other and fuse only at the tips and only between individuals in the same species.

When do oomycota only fuse at?

At the time of the zygospore.

What is a yeast?

A single celled organism.

Can yeast produce hyphae?

Only some yeast can produce hyphae

Are most anamorphs or telomorphs?

Most yeasts are anamorphs

How do yeast reproduce?

By budding or fission

What do they produce?

Some produce asci, some produce basidia

What is found in the yeast single cell?

single nucleus, conspicious vacuole

What is an example of a yeast that goes through budding?

Saccharomyces cerveisaia

Some yeasts are dimorphic, what does this mean?

Depending on the environmental conditions they can either become hyphae or be yeast.

What would a wetter environment produce?

Yeast

How do yeasts grow?

How do yeasts grow?

Often bud from multiple locations on the surface of the cell. Small outgrowth at bud site. Gets longer and longer before forming a round shape. New wall material is synthesized. Nucleus migrates to bud and divides when the bud reaches adult size. Septum develops by a ring of chitin developing at bud site and expanding inward until a complete chitin plate is formed. Leaves a bud scar. We can use fluorescent dyes that attach to chitin to count the bud scars.

Bud Scars:


Saccharomyces: multipolar:


-Always buds from new location


-100 in theory; 40 in reality


-Others: bipolar:


-From the poles of the yeast cell


-In theory immortal


-Typical content of chitin in yeasts: 1-2%


-All in the bud scars

Taxonomy complicated by lack of distinguishing morphological characteristics


-Molecular techniques now being used -Monophyletic (Ascomycetous types)


-Different from fission yeast (Schizosaccharomyces)


-Don’t bud; form segments that fragment -arthrospores

Roles of hyphal walls


-Structural


-Determines style of growth: hyphal or yeast


-How components are assembled and bonded


-Interface with the environment


-Protects against osmotic lysis


-Regulates the pass of molecules through wall pores


-Contains melanin:


- Protection against UV


- Lytic enzymes of other organisms

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What are some physiological functions of the walls?

They are binding sites for enzymes, since disaccharides and peptides need to be degraded.


They are also used to interact with other organisms.

What are the main components of the wall?

Predominantly composed of polysaccharides.

There are two major types of walls of fungi, what are they?

Structural and matrix.

What are structural walls consisted of?

Straight chained polymers(fibril)

What are matrix walls consist of?

Cross-linked coated polymers(fibril)

What is the cell wall component ion Chytrids, Ascomycetes, and Basidomycetes?

Chitins and glucans.

What are chitins and glucans?

Straight chains, and branched polymers.

What are zygomycetes cell walls composed of?

Mixture of chitins and polymers of uronic acid(glucuronic acid/mannoproteins)

What are oomycota(straminopila) cell walls composed of?

Cellulose and glucans.

What are the four layers of neurospora crass?

Outermost layer: glucans


Next: glycoproteins


Next: layer of protein


Innermost: microfibrils embedded in protein


last: plasma membrane

How thick is this 4 layer neurospora crassa?

125nm thick



What about the hyphal tip?

50nm


inner layer of chitin, outer layer of protein

What is the general wall structure for all fungi?

Inner chitin or cellulose layer embedded in protein.




Out layer of proteins, glucans, mannins.



Yeast is the same plus what?

Outer layer of glycoproteins/polysaccharides


-important roles with interactions with other organsisms


-can protect against being engulfed by phagocytes by masking antigenic components of cell wall


-often influenced by growth conditions



Septa




Regular intervals in Ascomycetes, Basidiomycetes, and mitosporic fungi




-Purposes:Hyphal damage: plug lost of protoplasm


-Plug of coagulated protoplasm (Woronin Body) -Eaten or parasitized


-Which group of fungi are more vulnerable to damage?


-Oomycota and Zygomycota

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What can septa do for hyphae?

Provide structural support, conditions of water stress, can block pores and divide into individual cells

What kind of pore do Ascomycetes have?

-A large simple central pore(0.05-0.5um)


-Allows passage of organelles/nuclei


-Develop very quickly(few minutes)


-Ingrowing ring from lateral walls


-Localized proliferation of a glycoprotein reticulum

What kind of pore do basidiomycetes have?

-Have a simple pore when monokaryotic

When two strains join together what kind of pore do u get?

A dolipore septa form(dikaryon)

How big can the pore be?

(100-150nm)

What is it bound by ?

two flanges of amorphous glucans

What bracket the glucans?

Membranous structures



What are these membranous structures called?

Parenthosomes

What are these pores used for?

to allow Cytoplasmic continuity, can prevent passage of organelles/nuclei

Pores of septate fungi

Pores of septate fungi



How big is the nucleus in fungi walls?

1-2um and up to 20-25um

How many membranes does the nucleus have?

double membrane

Notable peculiarities:


-Nuclear membrane / nucleolus remain intact during cell division (mitosis)


-Prevents dispersal of nuclear contents in cytoplasm?


-No metaphase plate; randomly disperse


-All fungi still need microtubule organizing centre so chromosomes will separate properly.

Vast majority of nucleus are haploid, all other plants, animals and pseudo fungi are 2N

What does the phospholipid bilayer in fungi contain?

-Transmembrane proteins(nutrient uptake)


-Signal transduction


-Anchor enzymes, chitinase and glucanase: integral membranes, that produce and deposit polysaccharides chains

What membrane sterol is in fungi?

Ergosterol, this is what fungicides go after

What sterols do oomycota have in their plasma membrane?

B-sitosterol and phytosterols

What are the three main components in the secretory system?

Endoplasmic reticulumn, golgi apparatus, and membrane bound vesicles

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What is defined as the peripheral growth zone?

Point at which a cut on the hyphae does no affect growth or metabolism

Growth thought to involve to two processes




-Continuous extension of the plastic deformable tip


-Rigidification of wall behind the tip

Tips very sensitive to environmental or disturbance influences


Tips undergo ‘stop-switch-branch’ reaction

Chitin synthese

one of the major enzymes involved with forming chitin

Glucan synthase

Other major ennzyme that catalyses the glucan chains. Composes bulk of fungal cell wall. Through to arrive in vesicles as well. Inserted into wall at tip of hypha.

Negative autotropism: spores respond to touch of other spores

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