Download Traits of fungi: The mycelium: How is its structure related to the

Some major episodes in the history of life
Fungi
1. General characteristics of fungi
2. Ecological roles of fungi
3. The fungus life cycle
4. The four fungal phyla
Figure 31.9 Phylogeny of fungi
Traits of fungi:
1. Eukaryotic
2. Heterotrophic, with absorptive nutrition (exoenzymes)
3. Body made of hyphae—thin, long strands of cells
-interwoven net of hyphae is called a
mycelium
-cell walls usually composed of chitin
4. Dispersal via asexual and/or sexual spores
5. Unique life cycle, including a heterokaryotic stage
Septate hyphae (left) and nonseptate (or coenocytic) hyphae (right)
Learn to match structures in these groups to the stages of
the generalized fungus life cycle
Figure 31.2 Fungal structure
The mycelium: How is its structure
related to the absorptive nutrition of the
fungus?
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Figure 31.3-31.4 Examples of fungal hyphae
Mycelia
• Highly branched, have very high surface
area:volume ratio
– 1 cm3 of soil may contain 1 km of hyphae
• All parts of fungal body (except
reproductive structures) in close contact
with environment
• Interior of any cell is in close contact with
environment
One ecological role of fungi:
mycorrhizae
Fungal ecology
• Most fungi are decomposers
• Many fungi are parasites, causing
diseases in plants or animals
• A very few fungi are predators - eat very
small animals (nematodes) in the soil
• Fungi are always heterotrophs, but…
• Fungi are involved in important
mutualisms with plants and algae
“Mycorrhiza” = Fungus/root
(plural: mycorrhizae)
Plant
Soil Nutrients
Sugars
Fungus
• Some fungi attach to plant roots, forming a
“mycorrhiza”
• These fungi obtain nutrients from the soil and pass
some of them along to the plant
• In return, the fungus receives carbon (sugars) from
the plant
• One type of mycorrhiza, the ectomycorrhiza, is
usually a basidiomycete fungus on the roots of
conifers, oaks, eucalypts, and a few other trees
• Many of the mushrooms you see in the forest are
the basidiocarps or sexual fruiting bodies of
mycorrhizal fungi
Two main types of mycorrhizae
• Ectomycorrhizae form sheaths over the
outer surface of a root, and may grow into
the extracellular spaces of the root cortex,
but do not penetrate cell walls
2 main types:
1. Ectomycorrhizae
(pictured here;
mostly Basidio-,
some Ascomycota)
and
2. Arbuscular
Mycorrhizae
(formerly “endo-”,
all are
Glomeromycetes)
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Figure 37.12 Ectomycorrhizae and endomycorrhizae.
Two main types of mycorrhizae
• Ectomycorrhizae form sheaths over the
outer surface of a root, and may grow into
the extracellular spaces of the root cortex,
but do not penetrate cell walls
• Endomycorrhizae (arbuscular
mycorrhizae) extend into the interiors of
root cells
Figure 37.12 Ectomycorrhizae and endomycorrhizae.
Figure 31.123 Lichens: a symbiosis between a fungus (usually an ascomycete)
and a photosynthetic organism (alga or cyanobacterium). Usually presumed to
be a mutualism. Grow very slowly, can live for a very long time.
Figure 31.24 Anatomy of a lichen
Figure 31.5 Generalized life cycle of fungi (Layer 3)
**Notice the lack of a multicellular diploid stage
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Figure 31.9 Phylogeny of fungi
Fungi
1. General characteristics of fungi
2. Ecological roles of fungi
Basidiocarps
Flagellated zoospores
Ascocarps
Zygosporangia
(sporangium)
3. The fungus life cycle
4. The four fungal phyla
Learn to match structures in these groups to the stages of
the generalized fungus life cycle
Figure 31.11 Phylogeny of fungi
Chytridiomycota
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Chytrids and Zygomycetes
may be paraphyletic
‘early’ fungi: flagellated spores, zoospores
Lakes, ponds, soil
Some are saprobes, some parasitic
Some single celled, most have coenocytic
hyphae
• A ‘link’ to animal evolution? 1.5 billion years
animals and fungi diverged, but fossil evidence
is sparse!
Zygomycota
Chytrid ecology
• Mostly unicellular, some species form
colonies with hyphae
• Mostly saprobes (eat dead organisms),
some parasites
• Disease caused by a chytrid fungus
appears responsible for many cases of
amphibian decline
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Form a zygospore: resistant structures during sexual reproduction
About 1,000 species - variable life histories! Including molds,
parasites and commensal symbionts
Coenocytic hyphae, with septa only where reproductive cells are
found
Asexual phase: haploid spores develop in sporangia at the tips of
upright hyphae
When conditions get bad: sexual reproduction and the zygospore
Zygosporangium is a resistant multinucleate structure where
heterokaryotic nuclei fuse to form diploid nuclei that undergo
meiosis
When conditions improve: meiosis and the release of haploid spores
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Figure 31.12 The life cycle of the zygomycete Rhizopus (black bread mold)
Notice the lack of a
heterokaryotic
mycelial stage
Glomeromycota: AMF
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This is a ‘phylum?’ currently grouped
with the zygomycota
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They are classified as arbuscular
Mycorrhizal Fungi (AMF)
•
All (?) are asexual
•
They are symbionts - over half of
living fungi in soil are probably these!
•
Important commercially
Figure 37.12 Glomeromycota are arbuscular mycorrhizae (endomycorrhizae).
Ascomycota: sac fungi
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Figure 31.16 Ascomycetes (sac fungi): Scarlet cup (top left), “true” truffles
(bottom left), morel (right)
35,000 species! Marine, freshwater , terrestrial habitats
Produce sexual spores in saclike asci
Fruiting bodies: ascocarps
Variety of morphologies and life histories from single celled yeasts
to morels
Many are plant pathogens, many are saprobes, many live with algae
as lichens (about 40%)
Produce conidia - naked spores on conidiophores (asexual
reproduction)
Extensive heterokaryotic stage
Figure 31.17 The life cycle of an ascomycete
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Figure 31.17 The life cycle of an ascomycete
Figure 31.18 Basidiomycota (club fungi)
•30,000 species
•Long lived
dikaryotic mycelia
•Basidium: transient
diploid stage
•Important saprobes
(can decompose
lignin)
•Fruiting bodies are
basidiocarps
•Asexual
reproduction not as
common
Figure 31.20 The life cycle of a mushroom-forming basidiomycete
aka fruiting body,
basidioma
Basidiomycete Gills, and their attached basidia and basidiospores.
Basidiomycetes are named after their basidia.
hymenial layer
False truffles: spherical, underground,
mammal-dispersed basidiomycete
fruiting bodies evolved from mushroom
ancestors
Figure 31.19 A fairy ring
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Table 31.1 Review of Fungal Phyla
Not always!
Always has
microscopic
basidia
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