Transcript Chapter 30 Fungi: Recyclers, Killers, and Plant Partners

Chapter 30 Fungi:
Recyclers, Killers, and
Plant Partners
Biology 101
Tri-County Technical College
Pendleton, SC
Fungi Characteristics
ALL are heterotrophic organisms with
absorptive nutrition
NO photosynthetic members of this kingdom
Some are saprobes that absorb nutrients
from dead matter; others are parasites that
absorb nutrients from living hosts; and some
live in mutualism with other organisms
Unicellular and multicellular species
Characteristics, cont.
Cell walls (if present) possess complex
polysaccharide chitin
Most fungi have complex body forms
All the fungi produce spores
asexual, sexual, or both
Only one phylum (Chytridioimycota)
has spores or gametes that possess
flagella
What a body…
Most fungi NOT unicellular but whether
they can be called multicellular is
questionable
Vegetative (feeding) body of fungus
called a mycelium
Mycelium composed of rapidly growing
individual tubular filaments called
hyphae (hypha)
Body, cont.
Within most hyphae, there is NO division into
separate cells so organelles (even nuclei) can
move around (COENOCYTIC HYPHAE)
May be more appropriate to call fungi
“multinucleate”
Some hyphae are subdivided into cell-like
compartments by incomplete cross walls
called septa (septum)
Those with septa said to have SEPTATE
HYPHAE
Fungal Body Visual
Body, cont.
Certain modified hyphae called rhizoids
anchor members of Chytridiomycota to their
substrate
Tubular body of fungus give it a unique
relationship with its environment
Has enormous surface area-to-volume
ratio which is marvelous adaptation to
absorptive nutrition
Able to tolerate highly hypertonic
environment and temperature extremes
Modes of Reproduction
Asexual reproduction takes many forms
production of haploid spores within
sporangia
production of naked spores at tips of
hyphae (condia = dust)
Cell division by unicellular fungi (equal
division or asymmetrical division = bud)
Fragmentation by simple breakage of the
mycelium
Modes, cont.
Sexual reproduction rather unique because
often NO morphological distinction between
male/female individuals/structures
There is genetically determined distinction
between two or more mating types
Individuals of same mating type cannot mate
with each other but can mate with different
mating type
This prevents self-fertilization
More on the modes..yeehaw!!
In many fungi, zygote nuclei formed by
sex reproduction ONLY diploid nuclei in
life cycle
These nuclei undergo meiosis,
producing haploid nuclei that wind up in
spores
Haploid nuclei (either method)
germinate and nuclei divide mitotically
to produce hyphae
Enough on modes, already
Some use dikaryon stage to reproduce
sexually
Plasmogamy, karyogamy,
dikaryon, heterokaryon
No gamete cells, only gamete nuclei
These hyphae are neither 2N or N, but
rather they are dikaryotic (N + N)
Dikaryosis most significant genetic
peculiarity of fungi
Chytridiomycota
Aquatic microorganisms with cells walls
of chitin
Either parasitic or saprobic
Reproduce both asexually and sexually
Only fungi that have flagella at any life
cycle stage
Allomyces is best example
Zygomycetes
Have coenocytic hyphae and produce
NO motile cells
Zygote only diploid cell in life cycle
Rhizopus stolonifer is black bread mold
(and will hide on the onions…)
Can reproduce asexually and sexually
Ascomycetes
Distinguished by production of sacs called
asci (sexual reproduction structure)
Septate hyphae
Divided into two groups on basis of asci
Euascomycetes (true) possess ascocarp
(specialized fruiting structure that
contains/protects the asci)
Hemiascomycetes (half) do NOT possess
ascocarp
Ascomycetes, cont.
Hemiascomycetes are microscopic
with many unicellular species
Saccharomyces cerevisiae (yeast)
Reproduce asexually by “budding”
Sexual reproduction produces
ascospores
Euascomycetes include filamentous
fungi known as the “molds”
Ascomycetes, III
Many (euascomycetes) are parasites
(Chestnut blight/Dutch Elm disease)
Also includes the cup fungi: morels and
truffles
Penicillium (antibiotic/Chamembert &
Roquefort)
Asperigillus (soy sauce/sake/aflatoxins
**Reproduce asexually by means of condia
and sexually by a dikaryon
Basidiomycetes
Club fungi that includes puff balls, bracekt
fungi, commercial mushrooms, some
parasites, and some symbionts
Usually have septate hyphae
Basidium (swollen cell at tip of hyphae)
characteristic sexual reproductive structure
Basidiospores contains spores
Some have cap (pileus) which has gills on
underside
Great numbers of basidia develop on gills
Let’s talk sex..but quietly
Zygomycota reproduce sexually when
adjacent hyphae of two different mating
types release pheromones which cause them
to grown together
These hyphae produce gametangia that fuse
to form zygosporangia containing
zygospores
Zygosporangia develop thick, multilayered
walls that protect the zygospores
Zygomycota, cont.
Highly resistant zygospores may remain
dormant for months before their nuclei
undergo meiosis and a sporangium sprouts
Sporangium contains product of meiosis—
haploid nuclei that are incorporated into
spores
Spores disperse and geminate to form new
generation of haploid hyphae
Zygomycete Visual
Ascomycota
Enough on budding already…
Sexual reproduction includes formation
of dikaryon
Nuclei from male structure on one
hypha enter female making structure on
hypha of compatible mating type
Dikaryotic ascogenous (asciforming) hyphae develop from
dikarytoic female mating structure
Ascomycota, cont.
Introduced nuclei divide simultaneously with
host nuclei
Eventually asci form at tip of ascogenous
hyphae
Only with formation of asci, do nuclei finally
fuse
Nuclear division and meiosis of diploid
nucleus takes place within individual asci
Meiotic products incorporated into ascospores
that are ultimately released to begin new
haploid generation
Basidiomycota
Basidiomycota are the “club fungi”
After nuclei fuse in basidium, diploid
nucleus undergoes meiosis and four
haploid nuclei are incorporated into
haploid basidiospores which form on
tiny stalks
Basidiospores typically forcibly
discharged from basidia
Deuteromycota
Called the “imperfect” fungi
Mechanisms of sexual reproduction readily
distinguish members of four phyla from one
another
Many fungi, however, lack a sexual stage or
their stage has NOT yet be identified
Fungi not yet classified in one of four phyla
are placed together as “imperfect”
Is holding area for species whose sexual
reproduction stage (if any) has not been
identified
Mycorrhiza
Mycorrhiza is mutualistic relationship between
root hairs of plant and a fungus
Ectomycorrhizae: fungus wraps around
root, >ing surface area for absorption of
water and minerals
Mass of fungi (like sponge) help hold water in area
of root
Infected roots branch extensively and become
swollen and club-shaped
Mycorrhiza, cont.
Endomycorrhizae: infection internal to root
with no hyphae visible on root surface
Fungus obtains organic compounds from
plant while increasing absorption of water
and minerals (esp. phosphorus) by plant
Fungus may provide certain growth hormones
and protect plant from attack by
microorganisms
Mycorrhiza, cont.
Been suggested this relationship ALLOWED
plants to survive move to land
Plants with active mycorrhizae are deeper
green and may resist drought and
temperature extremes between than plants of
same species with little or no mychorrhizae
development
Attempts to introduce plants to new areas
have fialed until bit of soil from native land
was provided
Lichens
Lichen is mutualistic relationship between a
fungus and a photosynthetic microorganism
(cyanobacterium or green algae)
Are found in all sorts of exposed habitats
Important pioneer organisms and help in the
soil cycle
Very sensitive to air pollution because they
are unable to excrete toxic substances they
absorb
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