2. Chapter 22
Fungal Anatomy
Multicellular
Body of almost all fungi is a mycelium, an
interwoven mass of threadlike filaments
called hyphae (singular, hypha)
Chitin cell walls
Hyphae of most species are divided into
many cells by partitions called septa
(singular, septum); each cell possesses
one or more nuclei
• Pores in the septa allow cytoplasm to stream
from one cell to the next
3. The Filamentous Body Chapter 22
of a Fungus
(a) Mycelium (c) Hyphal Cells (cutaway)
Haploid
Cytoplasm Nuclei
Septum
(b) Individual Hyphae
Pore
Cell Walls
5. Chapter 22
Fungal Nutrition
Three major types of heterotrophic nutrition
• Saprophytic—digestion of dead organisms
• Parasitic—digestion of live organisms
• Symbiotic—mutual benefit of two
independent organisms
6. Chapter 22
Fungal Reproduction
Asexual
• Fragmentation
• Asexual spore formation
– Haploid mycelium produces haploid asexual
spores by mitosis
– Spores germinate and develop into a new
mycelium by mitosis
Results in the rapid production of
genetically identical clones
8. Chapter 22
Fungal Sexual Reproduction
Typically occurs under conditions of
environmental change or stress
• Neighboring haploid mycelia of different, but
compatible mating types come into contact
with each other
• The two different hyphae fuse so that the
nuclei share a common cell
• The different haploid nuclei fuse to form a
diploid zygote
• Zygote undergoes meiosis to form haploid
sexual spores
9. Zygomycete Life Cycle (a) Chapter 22
Sporangia Spores
(haploid)
Diploid
2n
Zygospore Haploid
germinates 1n
Hyphae of
opposite mating
types fuse to
(b) Photo of Sporangia form zygospore.
10. Zygomycete Life Cycle (b) Chapter 22
Hyphae of
opposite mating
types (+ & -) fuse.
Zygospore
germinates
MEIOSIS NUCLEI FUSE
Haploid
1n Diploid
Zygospore
Diploid formed
2n
11. Chapter 22
Classification of Fungi
Fungi have been assigned to four phyla
based upon the way they produce
sexual spores
• Chytridiomycota (chytrids)
• Zygomycota (zygote fungi)
• Ascomycota (sac fungi)
• Basidiomycota (club fungi)
13. Chapter 22
The Chytrids
Chytrids
• Most are aquatic
• Reproduce both asexually and sexually
• Form flagellated spores that require
water for dispersal
• Figure 22-4, p. 426, illustrates the chytrid
fungus Allomyces in the midst of sexual
reproduction
15. Chapter 22
The Chytrids
Most feed on dead aquatic material
Some species are parasites of plants
and animals
• One chytrid species is a frog pathogen
believed to be a major cause of the
current worldwide die-off of frogs
Primitive chytrids are believed to have
given rise to the other groups of
modern fungi
16. Chapter 22
Zygomycetes
Most live in soil or on decaying plant or
animal material
Reproduce both asexually and sexually
• Sexual spores are thick-walled zygospores
During asexual reproduction:
• Haploid spores are produced via mitosis
in black spore cases called sporangia
• Spores disperse and germinate to form
new haploid hyphae
17. Chapter 22
Zygomycetes
During sexual reproduction
• Two hyphae of different mating types come
into contact and fuse
• Nuclei fuse to form a diploid zygospore, a
tough, resistant structure that can remain
dormant for long periods until conditions are
favorable
• Meiosis occurs as the zygospore germinates
• Resulting spores disperse and germinate to
form new haploid hyphae that can enter either
the asexual or sexual cycle
21. Chapter 22
Ascomycetes
Live in a variety of marine, freshwater,
and terrestrial habitats
Reproduce both asexually and sexually
• Sexual spores form in saclike asci
During asexual reproduction
• Haploid spores are produced via mitosis
at the tips of specialized hyphae
• Spores disperse and germinate to form
new haploid hyphae
22. Chapter 22
Ascomycetes
During sexual reproduction
• Two hyphae of different mating types
come into contact and fuse, resulting in
the formation of a fruiting body
24. Chapter 22
Ascomycetes
Better known examples include
• Most of the food-spoiling molds
• Morels and truffles (edible delicacies)
• Penicillium, the mold that produces
penicillin (the first antibiotic)
• Yeasts (single-celled fungi)
25. Chapter 22
Some Ascomycetes
(a) Scarlet Cup Fungus
(b) Morel
26. Chapter 22
Basidiomycetes
Live in a variety of marine, freshwater,
and terrestrial habitats
Usually reproduce sexually
• Sexual spores form in club-shaped
basidia
During sexual reproduction:
• Two hyphae of different mating types
come into contact and fuse, resulting in
the formation of a fruiting body
27. Chapter 22
Basidiomycete Life Cycle
Haploid Nuclei Fusion forms
diploid zygote.
Basidia
SIS on gills
MEIO
Basidiospores
(haploid)
Diploid Mushroom gills
2n bear reproductive
Haploid basidia.
1n
28. Chapter 22
Basidiomycete Life Cycle
Basidiospores
(haploid)
Basidia
on gills
Hyphae aggregate
to form mushroom
“+” Mating
Strain “-” Mating
Strain
Basidiospores germinate
forming hyphae (haploid).
+
Diploid
-
Hyphae fuse, but
2n haploid nuclei
Haploid remain separate
1n in binucleate cells
29. Chapter 22
Basidiomycetes
Better known examples include
• Mushrooms (some are edible, others are
poisonous)
• Puffballs
• Shelf fungi (decomposers of wood)
• Stinkhorns
• Rusts and smuts (plant parasites)
• Yeasts
31. Chapter 22
Fairy Rings
A fairy ring is a circular pattern of
mushroom growth
Fairy rings form at the leading edge of
an expanding underground fungal
mycelium
• The wider the diameter of the ring, the
older the mycelium
• Some fairy rings are estimated to be 700
years old
33. Chapter 22
Symbiotic Relationships
A symbiosis is a close interaction
between organisms of different species
over an extended period of time
The fungal member of a symbiotic
relationship may be harmful (a parasite
of plants or animals) or beneficial
(lichens and mycorrhizae)
34. Chapter 22
Lichens
Lichens are symbiotic associations
between fungi (usually an ascomycete)
and algae or cyanobacteria
• Fungus provides photosynthetic partner
with shelter and protection
• Photosynthetic partner provides fungus
with food (sugar)
36. Chapter 22
Lichens
Grow on a wide variety of materials
(soils, tree trunks and branches, rocks,
fences, roofs, and walls)
Are able to survive environmental
extremes (newly formed volcanic
islands, deserts)
Are very diverse in form
38. Chapter 22
Mycorrhizae
Mycorrhizae (singular, mycorrhiza) are
symbiotic associations between fungi
and plant roots
• Fungus provides plant with water, minerals,
and organic nutrients it absorbs from the
soil
• Plant provides fungus with food (sugar)
80% of plants with roots have mycorrhizae
Relationship may have helped plants
colonize land
40. Chapter 22
Recyclers
Fungi are Earth’s undertakers, feeding
on the dead of all kingdoms
Fungal saprophytes (feeding on dead
organisms) release extracellular
substances that digest the tissues of
the dead and liberate carbon, nitrogen,
phosphorus compounds, and minerals
that can be reused by plants
41. Chapter 22
Fungi Attack Plants
Fungal parasites cause the majority of
plant diseases
• Ascomycete parasites cause Dutch elm
disease and Chestnut blight
• Rusts and smuts are basidiomycete
parasites that cause considerable
damage to grain crops
43. Chapter 22
Fungi Cause Human Diseases
Athlete’s foot, jock itch, and ringworm
are caused by fungi that attack the skin
Valley fever and histoplasmosis are
caused by fungi that attack the lungs
• Infection occurs when victim inhales
spores
Most vaginal infections are caused by
the yeast Candida albicans
45. Chapter 22
Fungi Produce Toxins
Claviceps purpurea (an ascomycete)
produces several toxins
• Infects rye plants and causes ergot
disease
• Symptoms of ergot poisoning include
vasoconstriction of blood vessels,
vomiting, convulsive twitching,
hallucinations, and death
Penicillin
• First antibiotic to be discovered
• Used to combat bacterial diseases
47. Chapter 22
Fungi Contribute to Gastronomy
Certain ascomycete molds impart flavor to
some of the world’s most famous cheeses
• Roquefort
• Camembert
• Stilton
• Gorgonzola
Yeasts are used in the production of wine,
beer, and bread
Wine is produced when yeasts ferment fruit
sugars; ethyl alcohol is retained, while CO2
is released
48. Chapter 22
Fungi Contribute to Gastronomy
Beer is derived when yeasts ferment sugars in
germinating grains (usually barley); ethyl
alcohol and CO2 are retained
Bread rises when yeasts ferment sugar that
has been added to bread dough; both ethyl
alcohol and CO2 escape during baking
Some fungi are consumed directly
• Mushrooms (a basidiomycete)
• Morels (an ascomycete)
• Truffles (an ascomycete)
50. Chapter 22
Fungal Ingenuity
The truffle has evolved an effective
adaptation for dispersal of its spores
• Releases an odor which causes pigs and
other animals to dig it up, scattering
spores to the winds
The zygomycete Pilobolus has evolved
bulb tops that blast off, spreading
spores
(a) A fungal mycelium spreads over decaying vegetation. The mycelium is composed of (b) a tangle of microscopic hyphae, only one cell thick, (c) portrayed in cross section to show their internal organization.
These filaments of the chytrid fungus Allomyces are in the midst of sexual reproduction. The orange structures visible on many of the filaments will release male gametes; the clear structure will release female gametes. Chytrid gametes are flagellated, and these swimming reproductive structures aid dispersal of members of this mostly aquatic phylum.
FIGURE 22-2 Some fungi can eject spores A ripe earthstar mushroom, struck by a drop of water, releases a cloud of spores that will be dispersed by air currents.
(a) Top: During asexual reproduction in the black bread mold (genus Rhizopus), haploid spores, produced within (b) sporangia, disperse and germinate on food such as bread. The resulting haploid hyphae may complete the asexual cycle by producing sporangia and spores.
(a) Top: During asexual reproduction in the black bread mold (genus Rhizopus), haploid spores, produced within (b) sporangia, disperse and germinate on food such as bread. The resulting haploid hyphae may complete the asexual cycle by producing sporangia and spores.
FIGURE 22-3 Evolutionary tree of the major groups of fungi
FIGURE 22-4 Chytrid filaments These filaments of the chytrid fungus Allomyces are in the midst of sexual reproduction. The orange structures visible on many of the filaments will release male gametes; the clear structures will release female gametes. Chytrid gametes are flagellated, and these swimming reproductive structures aid dispersal of members of this mostly aquatic phylum
FIGURE 22-5 (part 1) The life cycle of a zygomycete Top: During asexual reproduction in the black bread mold (genus Rhizopus ), haploid spores, produced within sporangia, disperse and germinate on food such as bread. Bottom: During sexual reproduction, hyphae of different mating types (designated + and - on the bread) contact one another and fuse, producing a diploid zygospore. The zygospore undergoes meiosis and germinates, producing sporangia that liberate haploid spores.
FIGURE 22-5 (part 2) The life cycle of a zygomycete Top: During asexual reproduction in the black bread mold (genus Rhizopus ), haploid spores, produced within sporangia, disperse and germinate on food such as bread. Bottom: During sexual reproduction, hyphae of different mating types (designated + and - on the bread) contact one another and fuse, producing a diploid zygospore. The zygospore undergoes meiosis and germinates, producing sporangia that liberate haploid spores.
FIGURE 22-5 (part 3) The life cycle of a zygomycete Top: During asexual reproduction in the black bread mold (genus Rhizopus ), haploid spores, produced within sporangia, disperse and germinate on food such as bread. Bottom: During sexual reproduction, hyphae of different mating types (designated + and - on the bread) contact one another and fuse, producing a diploid zygospore. The zygospore undergoes meiosis and germinates, producing sporangia that liberate haploid spores.
FIGURE 22-6 The life cycle of a typical ascomycete Top: In ascomycete asexual reproduction, haploid hyphae give rise to stalked structures that produce haploid spores. Bottom: In sexual reproduction, haploid nuclei of different mating types fuse to form diploid zygotes that divide and give rise to haploid ascospores.
(a) The cup-shaped fruiting body of the scarlet cup fungus (b) The morel, an edible delicacy. (Consult an expert before sampling any wild fungus—some are deadly!)
The mushroom (top left) is a reproductive structure formed from aggregated hyphae made up of cells that each contain two haploid nuclei. Within the cap, leaflike gills bear numerous basidia (top right). Within each basidium, the two haploid nuclei fuse, producing a diploid zygote. The zygote then undergoes meiosis, forming haploid basidiospores that are released from the basidia (right). After dispersal by wind or water, the basidiospores germinate, forming haploid hyphae. When hyphae of different mating types meet, some of the cells fuse. These cells, each containing two haploid nuclei, produce an extensive underground mycelium (bottom). Under appropriate conditions, portions of the mycelium aggregate, swell, and differentiate, poking up through the soil as mushrooms and completing the cycle.
The mushroom (top left) is a reproductive structure formed from aggregated hyphae made up of cells that each contain two haploid nuclei. Within the cap, leaflike gills bear numerous basidia (top right). Within each basidium, the two haploid nuclei fuse, producing a diploid zygote. The zygote then undergoes meiosis, forming haploid basidiospores that are released from the basidia (right). After dispersal by wind or water, the basidiospores germinate, forming haploid hyphae. When hyphae of different mating types meet, some of the cells fuse. These cells, each containing two haploid nuclei, produce an extensive underground mycelium (bottom). Under appropriate conditions, portions of the mycelium aggregate, swell, and differentiate, poking up through the soil as mushrooms and completing the cycle.
The giant puffball Lycopedon giganteum may produce up to 5 trillion spores. Shelf fungi, the size of dessert plates, are conspicuous on trees.
Mushrooms emerge in a fairy ring from an underground fungal mycelium, growing outward from a central point where a single spore germinated, perhaps centuries ago.
Most lichens have a layered structure bounded on the top and bottom by an outer layer formed from fungal hyphae. Attachments formed from fungal hyphae emerge from the lower layer and anchor the lichen to a surface, such as a rock or a tree. An algal layer in which the alga and fungus grow in close association lies beneath the upper layer of hyphae.
A colorful encrusting lichen, growing on dry rock, illustrates the tough independence of this symbiotic combination of fungus and alga.
Hyphae of mycorrhizae entwining about the root of an aspen tree. Plants grow significantly better in a symbiotic association with these fungi, which help make nutrients and water available to the roots.
This basidiomycete pathogen destroys millions of dollars’ worth of corn each year. Even a pest like corn smut has its admirers, though. In Mexico this fungus is known as huitlacoche and is considered to be a great delicacy.
Yeasts are unusual, normally nonfilamentous ascomycetes that reproduce most commonly by budding. The yeast shown here is Candida, a common cause of vaginal infections.
Penicillium growing on an orange. Reproductive structures, which coat the fruit’s surface, are visible, while hyphae beneath draw nourishment from inside. The antibiotic penicillin was first isolated from this fungus.
Truffles, rare ascomycetes (each about the size of a small apple), are a gastronomic delicacy.
The delicate, translucent reproductive structures of the zygomycete Pilobolus will literally blow their tops when ripe, dispersing the black caps with their payload of spores.
Arthrobotrys , the nematode (roundworm) strangler, traps its nematode prey in a nooselike modified hypha that swells when the inside of the loop is contacted.
