Chapter 30
Lecture 11
Fungi: Recyclers, Pathogens,
Parasites, and Plant
Partners
Dr. Angelika Stollewerk
Fungi
Aims:
• To understand the basic biology of fungi
• To show the diversity in the kingdom
of fungi
• To introduce fungal associations
Fungi
Aims:
•
To understand the basic biology of fungi
•
To show the diversity in the kingdom of fungi
•
To introduce fungal associations
These lecture aims form part of the
knowledge required for learning outcome 2:
Describe basic organism structure and
diversity (LOC2).
Fungi
Essential reading
• pages 650-663
Recommended reading
Pages 74-75: 4.3 What are the characteristics
of eukaryotic cells (This will be covered in
depth in SEF032 Molecules to cells, but it is
useful background here)
30 Fungi: Recyclers, Pathogens, Parasites, and Plant Partners
• 30.1 How Do Fungi Thrive in Virtually
Every Environment?
• 30.2 How Are Fungi Beneficial to
Other Organisms?
• 30.3 How Do Fungal Life Cycles
Differ from One Another?
Fungi and animals are descended from a common
ancestor: A unicellular eukaryote with a flagellum
Figure 30.1 Fungi in Evolutionary Context
Fungi and animals are descended from a common
ancestor: A unicellular eukaryote with a flagellum
Synapomorphies that distinguish the fungi:
• Absorptive heterotrophy
• Chitin in cell walls
30.1 How Do Fungi Thrive in Virtually Every Environment?
Absorptive nutrition
• Saprobes: absorb nutrients from dead
organic matter
• Parasites: absorb nutrients from living
hosts
• Mutualists: both partners benefit
Figure 30.2 Phylogeny of the Fungi
Bread mold
Mushrooms
30.1 How Do Fungi Thrive in Virtually Every Environment?
Yeasts: Unicellular members of the zygomycetes,
ascomycetes, and basidiomycetes.
Budding: mitosis followed by asymmetrical cell division.
30.1 How Do Fungi Thrive in Virtually Every Environment?
Multicellular fungi:
• Body is a mycelium—composed of
tubular filaments called hyphae.
• Hyphae cell walls have chitin.
• Some hyphae have incomplete cross
walls or septa, and are called septate.
• Hyphae without septa are called
coenocytic.
Figure 30.4 Most Hyphae Are Incompletely Divided into Separate Cells
mycelium
Septate hypha
Septum
Coenocytic
Hypha
(No septa)
30.1 How Do Fungi Thrive in Virtually Every Environment?
Rhizoids: modified hyphae for anchoring.
Hyphae can grow 1 kilometer a day!
Hyphae may reorganize to form a fruiting body such
as a mushroom.
A fungal mycelium has a large surface area-to-volume
ratio.
Good for absorptive nutrition;
But water loss also high—fungi are mostly in moist
environments.
30.1 How Do Fungi Thrive in Virtually Every Environment?
Many fungi can tolerate hypertonic environments.
Many fungi tolerate temperature extremes.
Fungi exploit many nutrient sources:
Saprobes get their energy, carbon, and nitrogen
directly from dead organic matter.
30.1 How Do Fungi Thrive in Virtually Every Environment?
Fungi exploit many nutrient sources:
Parasites:
Facultative
Obligate
Hyphae can invade plant tissues, and may
produce haustoria, projections that press
into cells without breaking through the
plasma membranes.
Figure 30.5 Attacks on a Leaf
hyphae
Haustorium
Fungal
spore
30.1 How Do Fungi Thrive in Virtually Every Environment?
Some parasitic fungi are pathogens.
Fungi are the most important pathogens in plants.
Predatory fungi trap
microscopic
organisms.
Figure 30.7 Spores Galore
Fungi reproduce rapidly when nutrient supplies dwindle.
30.2 How Are Fungi Beneficial to Other Organisms?
Saprobic fungi (along with bacteria) are the major
decomposers on Earth.
• Earth’s “rubbish disposal”
• Soil formation
• Recycling nutrient elements
Mould growth and
decomposition on
bread and fruit
30.2 How Are Fungi Beneficial to Other Organisms?
Symbiotic (close, permanent
association), mutualistic (both partners
benefit) relationships:
Lichens
Mycorrhizae
30.2 How Are Fungi Beneficial to Other Organisms?
Lichens: fungus + photosynthetic organism
• Fungi—mostly ascomycetes
• Photosynthetic partner—cyanobacterium
or alga, or both.
• Species are named for fungal component.
30.2 How Are Fungi Beneficial to Other Organisms?
Lichens:
• Can survive harshest environments on Earth.
• Very sensitive to toxic compounds—good indicators
of air pollution.
Figure 30.9 Lichen Anatomy
30.2 How Are Fungi Beneficial to Other Organisms?
Mycorrhizae: Association between
plant roots and fungal hyphae.
Ectomycorrhizae—fungus wraps
around the plant roots.
Web of hyphae penetrates soil
around roots, increase surface area
for water and mineral absorption.
30.2 How Are Fungi Beneficial to Other Organisms?
Mycorrhizae: Association between
plant roots and fungal hyphae.
Arbuscular mycorrhizae: hyphae
enter root and penetrate cell walls,
but not plasma membrane.
Figure 30.10 Mycorrhizal Associations
30.2 How Are Fungi Beneficial to Other Organisms?
Mycorrhizae are essential to almost all
vascular plants to increase water and
mineral uptake.
The fungus gets sugars and proteins
from the plant.
Fungus may also protect plant against
disease organisms.
30.2 How Are Fungi Beneficial to Other Organisms?
Evolution of mycorrhizal associations
may have been an important step for
plants to colonize land.
Plant roots secrete a chemical signal
that enables the fungi to find them.
30.2 How Are Fungi Beneficial to Other Organisms?
Endophytic fungi: living in
aboveground parts of plants.
Produce alkaloids, chemicals that help
give resistance to pathogens and
herbivores, and stresses such as
drought.
30.2 How Are Fungi Beneficial to Other Organisms?
Some leaf-cutter ants “farm” fungi:
Fungus grows on leaf bits and produces special
fruiting bodies—gongylidia. Ants feed on the
gongylidia. The “gardens” consist of one single
clone of fungus. Other fungi are killed by
substances in the ant faeces.
Figure 30.11 Keeping Fungal Interlopers Away (Part 1)
Figure 30.11 Keeping Fungal Interlopers Away (Part 2)
30.3 How Do Fungal Life Cycles Differ from One Another?
Asexual Reproduction in Fungi:
• Production of haploid spore in sporangia.
• Production of naked spores called conidia.
• Cell division by unicellular fungi—fission
or budding.
• Breakage of the mycelium.
30.3 How Do Fungal Life Cycles Differ from One Another?
Sexual reproduction:
Mating types are genetically different, but
not physically different. Individuals of the
same type cannot mate.
30.3 How Do Fungal Life Cycles Differ from One Another?
Sexual reproduction:
In a haplontic life cycle, the zygote is the
only diploid stage.
Some groups have a unique n + n stage
called a dikaryon.
Some groups have alternation of
generations.
Figure 30.12 Asexual and Sexual Reproduction in a Fungal Life Cycle
Generalised
fungal
life cycle
Fusion of
cytoplasm
Fusion of
nuclei
30.3 How Do Fungal Life Cycles Differ from One Another?
Alternation of Generations: Chytrids
Flagellated male and female gametes.
Multicellular haploid stage may be a “filter”
for harmful mutations.
Multicellular diploid stage includes a
structure that can withstand freezing and
drying.
Figure 30.13 Sexual Life Cycles Vary among Different Groups of Fungi (A) Chytrids
Haploid
Sporangium zoospores
Multicellular
diploid
chytrid
Multicelluar
haploid chytrid
female
male
gametangium
Fertilization
30.3 How Do Fungal Life Cycles Differ from One Another?
All other fungal groups do not have
flagellated gametes.
Plasomogamy: cytoplasms of individuals
of different mating types fuse.
Karyogamy: the nuclei fuse to form a
diploid zygote.
Liquid water is not required for
fertilization.
30.3 How Do Fungal Life Cycles Differ from One Another?
Many species lack a sexual stage—now
classified using DNA sequencing.
Deuteromycetes or “Imperfect Fungi”—
polyphyletic group of species that have
not yet been placed in any existing group.
25,000 species
Table 30.1 A Classification of the Fungi
Figure 30.17 Two Cup Fungi
Amanita muscaria
Fungi
Check out
30.1 Recap, page 654
30.2 Recap, page 659
30.3 Recap, page 663
30.1 Chapter summary, page 668 see WEB/CD Activity 30.1
30.2 Chapter summary, page 668
30.3 Chapter summary, page 668 see WEB/CD Activities 30.1
and 30.2
Self Quiz
Pages 668-669: Chapter 30 questions 1-4 and 10
Fungi
For Discussion
Page 669: Chapter 30 questions 1, 2, 4, 5, 6, 7 and 8
Key terms:
absorptive heterotroph, absorptive nutrition, Ascomycetes
(Ascomycota), ascospores, ascus, basidium, Basidiomycetes
(Basidomycota), biotin, chitin, Chytrids (Chytridiomycota),
coenotypic, conidia, cyanobacteria, decomposer, dikaryon,
ectomycorrhizae, endomycorrhizae, facultative parasite,
haustoria, heterokaryon, hypertonic, hypha (pl. hyphae),
karyogamy, lichen, mutualisitic, mycelium (pl. mycelia),
mycorrhizae, nematode, pathogen, plasmogamy, rhizoid,
saprobes, saprotophs, septate, septum (pl. septa), soredium
(pl. soredia), sporangium (pl. sporangia), spores, symbiotic,
thallus, thiamin, yeasts, Zygomycetes (Zygomycota), zygote