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Fungi
Fungal Characteristics:
• Eukaryotic Multicellular Kingdom
• Feed by Absorptive Nutrition
• Tubular cell shape, called Hyphae
– Septate or aseptate hyphae
• Chitin cell walls
• Store sugar alcohols
• Divisions determined by sexual
reproduction
• Reproduce by making spores
Nutrition and Habits
• Saprobes- decomposers
– exoenzymes
• Parasitic fungi• Mutualistic Fungi-
Hyphae Structure
• Mycelium: whole extensive organism
• Hyphae- tubular, typical fungal cell
– Septate hyphae have internal walls with pores that allow
smaller organelles to migrate
Septum
Hyphae types
• Most fungi are multicellular
• Septate have have incomplete cell wall
divisions with pores
• Coenocytic fungi, or aspetate are
multinucleate with free flowing
cytoplasm
– repeated mitosis without cytokinesis.
Structure of hyphae
Cell wall
Cell wall
Nuclei
Pore
Septum
(a) Septate hypha
Nuclei
(b) Coenocytic hypha
Hyphae Growth
• Rapid growth by Cytoplasmic streaming.
• Mycelia grow in length not girth, with
branching
• Most Fungi are nonmotile
• Mitosis: Nuclear envelope remains intact
with the spindle apparatus inside.
• Nuclei can migrate
– n+n pairs
• Produce chemicals
Antibiotics
Staphylococcus
Penicillium
Zone of
inhibited
growth
Anti-fungal drugs
• Fungi have ergosterol in their
membranes for fluidity ( animals
have cholesterol)
• Target for drug activity – binds up
and makes membrane porous.
Haustoria in plants
• modified hyphae that grow into plant cell
walls without piercing plasma membrane
• Allow for nutrient exchange
• May persist without killing host cell
Common in parasitic,
and mutualistic
fungi like mycorrhizae
Spores of all types !!!!
• Spore= A haploid cell for dispersal. Grows
into a new fungus.
• Trillions released from a single fruiting
body- from a Sporangia
• Sexual spores are meiospores.
• Asexual spores are mitospores.
• May be produced endogenously or
exogenously.
• Carried by wind, water.
Figure 31.5 Generalized life
cycle of fungi (layer 1)
Key
Haploid (n)
Heterokaryotic
(unfused nuclei from
different parents)
Diploid (2n)
Heterokaryotic
stage
PLASMOGAMY
(fusion of cytoplasm)
KARYOGAMY
(fusion of nuclei)
SEXUAL
REPRODUCTION
Mycelium
Zygote
Fungi general life cycle
Key
Haploid (n)
Heterokaryotic
(unfused nuclei from
different parents)
Diploid (2n)
Heterokaryotic
stage
PLASMOGAMY
(fusion of cytoplasm)
KARYOGAMY
(fusion of nuclei)
SEXUAL
REPRODUCTION
Zygote
Mycelium
MEIOSIS
GERMINATION
Spores
Spore-producing
structures
Generalized fungal lifecycle
Key
Haploid (n)
Heterokaryotic
(unfused nuclei from
different parents)
Diploid (2n)
Heterokaryotic
stage
PLASMOGAMY
(fusion of cytoplasm)
KARYOGAMY
(fusion of nuclei)
Spore-producing
structures
Spores
ASEXUAL
REPRODUCTION
SEXUAL
REPRODUCTION
Zygote
Mycelium
MEIOSIS
GERMINATION
GERMINATION
Spores
Spore-producing
structures
General fungal lifecycle
1. Spore germinates, grows into mycelium.
2. Mitospores may be produced
3. Plasmogamy Hyphae of different mating
types grow together, exchange nuclei
and become n+n (dikaryotic).
4. Dikarytotic state may live for many
years.
5. In hyphal tips, karyogamy followed by
meiosis.
6. Meiospores are produced
Fungal Diversity
• More than 100,000 species of fungi
• Chytrids are the
aquatic ancestral group
to the other divisions
• Divisions by sex
Arbuscular
mycorrhizal
fungi
Sac
fungi
Club
fungi
Ascomycota
Basidiomycota
Zygomycota
Chytridiomycota
Zygote
Chytrids fungi
Glomeromycota
Phylogeny of fungi
Fungal Divisions
Chytridyomycota –
• Aquatic, with flagellated
zoospores
Zygomycota = zygospores.
• Resistant zygote sporangium
Glomeromycota= zygospores
• arbuscular mycorrhizae.
Ascomycota = ascospores
• Endogenous meiospores
Basidiomycota = basidiospores
• Exogenous meiospores
Deuteromycetes – imperfect,
• no sexual reproduction
Molds – rapidly growing, asexually
reproducing fungi
• Most also have non-mold sexual
stages
• The mycelia of these fungi grow as
saprobes or parasites on a variety of
substrates
Yeasts- unicellular fungi growing
in liquid substrates
• Form new cells by budding
• Some can sexually reproduce, many form asci
• Some can ferment sugar to alcohol
Mycorrhizae
• Mutualism of Tree root and fungus.
• Gives tree water and minerals (desert
plants) and fungus gets carbohydrates.
Plant growth without
mycorrhizae is
often stunted
Mycorrhizae
Pathogenic Fungi
• Attack plants
– Rusts -red spores on multiple hosts
– Smuts –yeast like fungi rot plant
– Aflatoxins, Ergot –on rye.
• Attack People – Mycosis
– Ringworm, athlete’s foot
– San Joaquin Valley Fever
– Yeast, lung infections
• Attack insects, fish, etc.
Figure 31.25 Examples of
fungal diseases of plants
(a) Corn smut on corn
(b) Tar spot fungus on maple leaves
(c) Ergots on rye
Commercial Roles
• Fermentors: Fungi Are Eukaryotes
– Baking and Alcohol formation
– Sugar conc. above 5% inhibit aerobic enzymes, switch
to fermentation.
•
•
•
•
Biotechnology
Decomposers- Nutrient cycles in ecosystems
Antibiotics
Storage spoilers –
– 10- 50% of fruit harvest is lost to fungi
• Cheeses,
• edible mushrooms, truffles, morels
Lichens
• Symbiosis of
– Phycobiont, algae / cyanobacteria
– Mycobiont - fungi.
• Not individual organisms
• Primary colonizers of new land in
succession, and in tundra areas
• Soredia asexually reproduce lichen
– Fungi often reproduce on their own.
Fig. 31.17
Three growth forms:
1. Crustose – flat on
stones
2. Foliose- leaf-like as
in picture
3. Fruticose- upright
growing
Phycobiont in inner
layers protected by
fungi on top and
bottom
(a) A fruticose (shrub-like) lichen
(b) A foliose (leaf-like) lichen
(c) Crustose (crust-like) lichens
Chytridiomycota
• Chytrids use an absorptive mode of
nutrition and have chitin cell walls.
• There are a few unicellular chytrids, but
most form ceonocytic hyphae.
• Chytrids share key enzymes and
metabolic pathways with other fungal
groups, but not with the slime molds
• Ancestral to
other three
groups on land
• Forms flagellated
zoospores
Zygomycetes: Form resistant (Zygote)
Zygosporangia
• Zygosporangia are resistant to freezing and drying.
They are also ceonocytic.
• When conditions improve, the zygosporangia release
haploid spores that colonize new substrates.
• They can make both asexual
and sexual spores
– Pilobolus, can actually
aim their asexual sporangia
and shoot them off.
• Many molds are zygomycetes
• Have different mating types,
often labeled +, • Have ceonocytic hyphae
Zygomycete lifecycle
#10
#8
Zygosporangium formation
• +, - suspensor hyphae grow
together.
• Each tip cuts off a gametangia
with complete septa.
• Gametangia fuse into one
large heterokaryont.
• Nuclei pair up form many
diploid nuclei.
• Resistant wall forms on
Zygosporangium
• Before germination meiosis
takes place
• Forms sporangia, releasing
haploid spores
Asexual Spore
formation
• Haploid nuclei migrate to swollen
hyphal tip.
• Hyphal tip forms complete septum,
now a sporangium.
• Each nucleus forms a spore
around itself with cytoplasm,
endospores.
• Sporangium wall breaks.
• Spores blow away.
Glomeromycota
• Has some characteristics similar to
zygomycetes.
• DNA comparisons show then to be
their own group
• Form Arbscular endomycorrhizae
Arbuscular mycorrhizae
2.5 m
Plant cell wall
Ascomycota: Sac fungi produce sexual
spores in saclike asci
• Mycologists have described over 60,000
species of ascomycetes, or sac fungi.
• They range in size
and complexity
from unicellular
yeasts to
elaborate
cup fungi and
morels.
Ascomycetes are characterized by an extensive
heterokaryotic stage during the formation of ascocarps.
Fig. 31.10
Ascus formation
• Hyphal tip makes complete septum,
Nuclei fuse – a single 2n nucleus
• Meiosis – 4 haploid nuclei
• One mitotic division – 8 haploid nuclei
• Each nucleus cuts off some cytoplasm
and forms new wall, inside original hyphae
wall.
• 8 ascospores are forcibly ejected by
osmotic pressure.
• Different forms of ascocarp have evolved.
Ascospore formation
Mitosis
Meiosis
Zygote
N+N
Spore wall
Conidia
• Many Ascomycetes reproduce asexually by
producing enormous numbers of Conidia,
asexual spores, (exogenous mitospores)
which are usually dispersed by the wind.
Conidiophore
continuously
divides forming
more spores at
tip.
Basidiomycota
•
•
•
•
Typical Mushroom
Almost no asexual reproduction
Many mycorrhizae species
Oldest organism ?
Mushrooms caps have
basidia on gills.
The spores drop
beneath the cap and are
blown away.
• The life cycle of a Basidiomycete usually
includes a long-lived dikaryotic mycelium.
Fig. 31.12
Basidia formation